# AC 20-52 CHG 1: Maintenance Inspection Notes for Douglas DC-6/7 Series Aircraft

- Type: Advisory circular (guidance, not mandatory unless a rule or AD requires it)
- Status: Historical
- Approved: January 1, 1974
- Last reviewed: September 18, 2024
- This change: Canceled by memo signed by Steven Douglas (AFS-300), dated 12/20/2011.
- Family: AC 20-52
- Cancels: [AC 20-52](https://openairdocs.org/ac/20-52)
- 14 CFR parts: 1
- Pages: 94
- PDF: https://openairdocs.org/files/sha256/1a/d6/1ad6cf9bf9365db54de98494291862a073d5ebca8b9397d744446d368168bf99
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/AFA2DA134BEFEEED862569B60061D770.0001
- DRS record last changed: November 21, 2025
- Page: https://openairdocs.org/ac/20-52

## Versions

- [AC 20-52 CHG 1](https://openairdocs.org/ac/20-52) (Historical), approved Jan 1, 1974, 94 pages. Canceled by memo signed by Steven Douglas (AFS-300), dated 12/20/2011.

## Text

Each page's text from the PDF; open the PDF at a page with #page=N.

### Page 1

Federal Aviation Agency AC NO: AC 20-52 Consolidated reprint:

January 1974 - includes Change 1

**MAINTENANCE INSPECTLON NOTES FOR DOUGLAS DC-6/7 SERIES AIRCRAFT AUGUST 24, 1967**

DEPARTMENT OF TRANSPORATION Federal Aviation Administration

### Page 2

AC NO: AC 20-52’

AIRCRAFT EFFECTIVE :

August 24, 1967 SUBJECT : MAINTENANCE INSPECTION NOTES FOR DOUGLAS DC-6/7 SERIES AIRCRAFT 1 . PURPOSE. This handbook describes maintenance inspection notes which can be used for the maintenance support of certain structural parts of DC-6/7 series aircraft. .

2 . DESCRIPTION. Maintenance on the wing, fuselage, and empennage structure is reviewed with a view toward supplementing information currently available.' 3 l HOW TO GET THIS PUBLICATION.

a. Order additiona. copies of this publication from:

Department of Transportation Federal Aviation Administration Distribution Unit, HQ-438 Washington, D.C. 20590 b 0 Identify this publication as: Advisory Circular 20-52, Maintenance Inspection Notes for Douglas DC-6/7 Series Aircraft.

Flight Standards

### Page 4

AC 20-52 CliG I 8/24/67

**TABLE OF CONTENTS**

1. Introduction.'

2. Description., 3 l Background.

4 0 General Information.

5 0 Type of Construction.

6 0 General Inspection Tips.

7 0 Nondestructive Testing (NDT).

APPENDIX 1 Figure A-l Figure A-2 APPENDIX 2 Figure B-l Figure B-2 Figure B-3 Figure B-4 Figure B-5 APPENDIX 3 Figure C-l Figure C-2 Figure C-3 Figure C-4 Flap Hinge Bracket and Linkage.

Figure C-5 Outer Wing Panel Attach Point.

**APPENDIX 4 APPENDIX 5 APPENDIX 6 J**

**STATION CHARTS**

a. Outer wing and aileron.

b l Center wing flap.

c. Fuselage station.

(2 pages)

a. Vertical stabilizer and rudder.

b 0 Horizontal stabilizer and elevator.

Page i FUSELAGE CQ+PONENTS (5 pages) Fuselage Major Components.

Nose Section Assembly Floor Beam Structure, Slant Panel Structure, and Slant Panel Skin.

Lower Center Section Assembly Center Wing Section.

Lower Center Section Assembly Floor Beams (Stations 412 to 5001 Fuselage Floor Panels.

Page No, 1 1 1 1 2 2 4

CENTER WING SECTION Center Wing Section Spars.

Lower Center Section Assembly, Center Wing Section Structure.

Center Wing Trailing Edge Fuel Tank Spars Corrosion Resistant Seals.

1 2 l 1 2 (5 pages)

**FUSELAGE STATIONS**

WING STATIONS (15 pages) (18 pages) DC-6/7 MAINTENANCE INFORMATION (11 pages)

### Page 5

AC 20-52 CHG 1 7 Jul 72 Page No.

* APPENDIX 7 Figure G-1 Figure G-2 Figure G-3 Figure G-4 Figure G-5 Figure G-6 Figure G-7 Figure G-8 Figure G-9 Figure G-10 Figure G-11 Figure G-12 Figure G-13 X-6/7 STRUCTURAL INSPECTION ITEMS (21 pages) DC+6/7'Fuselage/Empennage.

DC-6/7 Center Wing, Emergency Exit Door Hinges.

Emergency Exit Hinge Cutouts.

Crew and Cargo Door Area. .

Vertical Stabilizer Front Spar to Fuselage Attach Fittings.

Main Entrance Door Area.

Fuselage Frames at Wing Upper Spar Cap Attach Area.

Horizontal Stabilizer-to-Tail Stub Front Spar Attach Fitting.

Wing Lower Front and Lower Center Spar Caps at Wing Station 30.

Wing Front, Center, and Rear Spar Caps at Station 60.

Lower Front Spar Cap Splice at M.L.G. Drag Brace Attach Fitting.

Lower Center Spar Cap Splice at Station 0.

1 9 10 11 12 13 14 15 16 17 l 18 19 20 21 *

### Page 6

AC 200 52 8124167 1 0 INTRODUCTION. This advisory circular provides maintenance information which can be used by mechanics, repair agencies, owners and operators in developing maintenance programs, making improvements in existing programs, .and conducting inspections and repairs on certain structural parts of Douglas K-6/7 airplanes. The material is based, in part, upon information made available through discussions with airline personnel who have maintained these types of airplanes for thousands of hours of time in service.

The intent of the circular is to impart some of this knowledge to other interested persons so that it is not lost.

. 2 0 DESCRIPTION. The circular contains guidance material for performing 3 l maintenance on wing, fuselage, and empennage structure. The information has been derived from service experience. It does not comprise a full and complete maintenance program for the subject aircraft but should be considered as supplemental maintenance data. Included in the circular are diagramatic sketches and station identifications of the wing, fuselage, and tail. The material concerns general information on corrosion and fatigue plus specific inspection notes which stress the examination of'a particular structural area,with suggestions as to the method of inspection.

In addition, there is a listing of selected maintenance difficulties which have been reported since 1964. .

**BACKGROUND. I**

a. Aircraft Use. The agency has realized that several different types of transport aircraft are being phased out of service by some airlines because of the availability of newer equipment. Such older aircraft are being purchased by other operators who may not be familiar with the scope of required maintenance and the means which have been used to keep the aircraft in a safe condition.

b 0 Maintenance "know how", Since maintenance "know how" is not transferred with the aircraft, the new operator generally goes through a learning cycle before he is able to rapidly pinpoint the important/ critical problem areas of the aircraft. In this respect, identification of known areas where structural problems have been experienced will help in the preparation of an initial maintenance program by a new operator. It also can serve as a guide to other operators who have not accumulated sufficient service experience to have knowl- .

edge of all the problem areas of the aircraft.

4 0 *GENERAL INFORMATION.

. a. Manufacturer's Bulletins. It must be emphasized .that the manufacturer has published several service bulletins concerning the inspection, repair, and modification of X-6/7 aircraft. Service Bulletins 406, 407 (DC-71, 857, and 858 (DC-61 highlight the importance of maintaining structural integrity on high-time aircraft with particular reference to areas known to have experienced crack and corrosion damage. Operators are urged to become conversant with the Par 1

### Page 7

Page 2 AC 20-52 8/24/67 manufacturer's recommendations and make certain that responsible maintenance personnel are knowledgeable on the subject.

b a Airworthiness Directive. It is emphasized that the material in this circular does not supersede any of the requirements of airworthiness directives issued under Part 39 of the Federal Aviation Regulations.

5 l TYPE OF CONSTRUCTION. The major structural components of the aircraft are- the wing group, tail group, and fuselage group. Appendixes 1 thru 5 provide detailed views of these components with station identification numbers.

a. The wing group is composed of left and right-hand outer wing sections and a center wing section. The wing group is a full cantilever-type structure, with channeled ribs, extruded and formed sheet stringers, and heavily built-up spars. Each outer wing section consistsof wing tip, an aileron, two aileron trim tabs, and a outer wing panel. .The center wing section consists of a left and right-hand wing flap, wing flap vane sections, and a center wing panel. The portion of the center wing section. that passes through the fuselage is integrated with the fuselage upon assembly. The center wing section includes the four engine nacelles (two on each side of the fuselage).

b, The tail group is composed of a vertical stabilizer, rudder, rudder , trim tab, left and right-hand horizontal stabilizers, left and righthand elevators, an elevator spring tab for each elevator, and two elevator trim tabs for each elevator. With the exception of the fabric-covered rudder and rudder trim tab, all control surfaces are covered with alclad aluminum alloy skin.

c. The fuselaEe group is an aluminum alloy, semi-monocoque type structure, constructed of longitudinal stiffeners, transverse frames and bulkhead, and f lush- rive ted stres sed skin. The fuselage is divide d into three main secti ons - the nos e se ction, upper and lower center S ection, and tail section assemblies.

6 l GENERAL INSPECTION TIk.

A. Visual Inspection. The primary structure of the aircraft is designed to provide resistance to variable forces imposed while in operation by dispensing the forces through a structural pattern of *'force flow" to the primary structural members of t he, w bing and fuselage. Exter indicat ions of failure, such as d istor 'ted skin, t ilted or s heared 'nal rivets, and torn, dented, cracked, or corroded skin are usually obvious.

Wrinkled skin, *'oil cans", and tilted rivets, adjacent to the obviously failed area often indicate secondary damage caused by transmission of stress from the failed area. Misalignment of doors and panels may indicate distortion of internal structure. Internal structural damage, although not always apparent, may be found by closely examining the exterior surface. For example:

Par 4

### Page 8

AC 20-52 8/24/67

(1) Buckled skin between rivets at the end of a stiffener or stringer could mean that the last attaching rivet has failed, or that the stiffener or stringer is buckled in the area of the skin buckle.

When a detailed inspection of the failed area is to be performed, functional parts should be actuated to determine if the failure has caused binding.

(2) Deep diagonal skin buckles, located over a frame, former,or rib could mean the member is distorted. When doubt exists concerning internal condition, the area in question should be opened and carefully inspected.

b 0 Fatigue Cracks. Examples of some areas in DC-6/7 series aircraft where cracks have been found are shown in Figure 1. Detailed repair instructions are provided in manufacturer's service bulletins and manuals.

UPPER and LOWER

**CENTER SPAR CAPS**

**CENTER SPAR**

**TO FUSELAGE STABILIZER**

**FUSELAGE NOSE SKIN**

PASSENGER, CARGO and CREW DOOR AREAS,

**HINGE CUTOUTS**

**STABILIZER**

**TIP ASSEMBLY FIGURE 1- AREAS SUBJECT TO FATIGUE CRACKS**

(1) Wing to fuselage attach fittings at center spar.

(2) Horizontal stabilizer and tail stub front spar attach fittings.

(3) Fuselage nose skin plating.

(4) Main crew/cargo entrance door latch plates.

(5) Rear fuselage frame and transverse floor beams.

c. Corrosion Prone Areas. Figure 2 refers to some of the corrosion prone areas in the aircraft. Manufacturer% service bulletins and manuals have been issued to provide detailed repair instructions.

Par 6

### Page 9

Page 4 AC 20-52 g/24/67

7. NONDESTRUCTLVE TESTING (NDT), iANDING GEA L--CABIN FLOOR - LR and SUPPORTS

PASSENGER, CARG ,?,,,sT PATH AR*?~ CREw D00Rs FIGURE 2 - AREAS SUBJECT TO CORROSION DAMAGE

(1) Exhaust path areas.

(2) Battery areas and vents.

(3) Lavatories, galleys, and cabin floors.*

(4) Wheel wells and landing gear.

(5) Joints between extruded aluminum sections and laminations.

Simply stated, nondestructive testing is preventative maintenance. This includes utilization of such maintenance tools as X-ray, ultrasonic, magnetic particles, eddy current, and dye penetrant.

a. Maintenance Inspection. NDT permits maintenance inspections without removing components from aircraft or tearing down complex assemblies.

Defects in various aircraft systems which would escape detection through normal visual inspection will be identified by NDT.

b . Training Required. Special NDT training is necessary to.make sure that the operator is capable of operating the equipment and interpreting the results. Also, many states require that an X-ray operator have an approved certificate for use of#X-ray in industrial applications. This is to minimize improper use of X-ray equipment with attendant health hazard.

Par 6

### Page 10

AC 20-52 g/24/67 , Page 5

AZRCRAFT STATION DIAGRAMS The wing, fuselage, and empennage station diagrams included in this document were developed for the DC-6B aircraft and areused as a general reference only. Several models of each of these aircraft were manufactured and have different station locator numbers based on the particular configuration. Since the defect areas generally apply to all models of both aircraft, the referenced area can be compared with a similar area and locator on the appropriate station diagram for the particular model of aircraft. For example, fuselage station 69 on the DC-6A/B may be station 129 on the DC-6 and 29 on the DC-7C.

### Page 12

1 .

’ .

NOTE: AILERON SlAtlONS SHOWNAT HINGE ?OINV$ A & IA8 locATlONs. STATIWSWTBRWWGA- AILERON TRIM TAB WA. wsMcTmHllwslRAT8a4s 462 105l7 DC-6

**FUSELAGE**

**LONCERONS**

INSPECTION REFEUENCEONlY C slATloNs iwQuoI 22 -13 -46 m 157 11t 69 41 4 -29 42 W~UIJSTRA~ FUSEUGE STATIONS DCdA/B STA 129 (Or-6) dmllor to Sm (DC+ STA 69 (DC-t) clmllar b STA 29 (DC-7C) 780 736 101 661 621 581 WI 500 464 421 281 341 ml 260 220 I70 I34 89 58 1194 II* Ill5 1071 1033 985 949 926 886 843 Ql

### Page 13

Appendix 1 AC 20-52 8124167 FIGURE A-2 N&E: RUDDBl STATIONS SHOWN

**ONLY AT HINGE POINTS AND TAB LOCATION.**

I-& m-w- I -77 ---- w--w 92 .-ww--m 107 E I- w-w- -A- -ma- - lzz ---w D me- w-w- 13f .

-ma- ---- - 152 167 me-- - -m--m I# ----.a P m-w- - 191 ---- - 211 224 v----m m-w- - 238 - 69 ai W 114 129 144 159 174 189 204 218 231 245‘ NOTE: ELEVAlat STATIONS SWN

**ONLY AT HINGE POINTS, TAB LOCATIONS AND SKIN LAPS.**

e a m- 152 155 -186 199 202

- --------- - 206 -- A -219

**B STATDWS 276 STATION CHARTS (SHEET 2 OF 2)**

### Page 14

FUSELAGE STATIONS STA 129 (DC-6) similar to STA 69 (DC-6A/B) STA 69 (k-7)- simi Iar to STA 29 (DC-7C) FIGURE B -1 FIGURE B-3 (SHEET 3 OF 5) LOWER CENTER. SECTION

ASSEMBLY CENTER WING SECTION (STA 412 TO 500) FUSELAGE MAJOR COMPONENTS (SHEET 1 OF 5) DWA/B .

### Page 15

Appendix 2 FIGURE B-2 AC 20-52 8/24/67 STA 2 STA 4 - STA 4 - WA22 - STA 41 ~mmmKN FIGURE B-2

NOSE SECTION ASSEMBLY FLOOR BEAM STRUCTURE SLANT PANEL STRUCTURE AND SLANT PANEL SKIN (SHEET 2 OF 5) DC4WB

### Page 16

AC 20-52 .

8124167 FIGURE B-3 Appendix 2 Page 3

**CENTERLINE OF**

**FUSELAGE**

SPAR WEB SPAIt CAP NOTE: WEWC l CENTER WING STRINGERS AND SPARS HAVE

**SPAR WEB 6UKHEAD -**

**ASSEMLY CAP**

**BEEN ELIMINATED WITHIN THE CENTER**

FUSELAGE SECTION FOR CLARITY, FUSELAGE STATIONS WURE B-3 STA 129 (DC-6) similar to STA 69 (DC-M/B) STA 69 (DC-7) similar to SfA 29 (DG7C)

LOWER CENTER SECTION ASSEMBLY CENTER WING SECTION STRUCTURE DlETAlLS (SHEET 3 OF 5) =AIlB c --

### Page 17

.

Appendix 2 FIGURE B-4 AC 2052 8/24/67 STA 412

FRONT SPAR STA 500 FUSELAGE STATIONS STA 129 (DC+ similar to STA 69 (DC-6wB) STA 69 (DC-7) simila to STA 29 (DC-7C) STA 460 .

TEE

REM UPPER SPAR CAP c II- EXTRUSION 4

**LOWER CENTER SECTION ASSEMBLY FLOOR BEAMS (STATIONS 412 TO SOO) (SHEET 4 OF 5) . DC-**

### Page 18

AC 20-52 B/24/67 , T&xmdix 2 - Page 5 FIGURE B-5 3 3 3 3 Gii& m75-0

SUPPORT PLATE ST FLoa IAbEL INSlALLAflOf vmw8 SEAT RACKS STA 938 STA 661\ s WITH FUSELAGE FLOOR PANELS (SHEET 5 OF S) DC& .

--

### Page 19

--

### Page 20

**FUSE CEN**

### Page 21

**LEFT-HAND WING WA 60 FIGURE C-2**

LOWER CENTER SECTION ASSEMBLY CENTER WING SECTION STRUCTURE (SHEET 2 OF 5) cn 0 z

### Page 22

Appendix 3 ACZO-52 8124167 FIGURE C-4 FIGURE C-3

CENTER WING TRAILING EDGE FUEL TANK SPARS AND CORROSION RESISTANT SEAL (SHEm 3 OF 5)

### Page 23

.

Appendix 3 -WING FLAP OPERATI I% LINK AC 20-52 B/24/67 FIGURE C-4 WING FLAP HINGE SM. 281 (LOOKING UP AT LOWER FLAP HINGE 6JkACKE’I)

**INSPECT ENTIRE CUTOUT AREA OF CLEARANCE SLOT FOR CRACKS.**

FIGURE c-4

**FLAP HINGE BRACKET AND LINKAGE WING STATION 281 (SHEET 4 OF 5)**

### Page 26

**FUSELAGE STATIONS- DC-6/7 AIRCRAFT INSPECTIONS**

**FUSELAGE**

STATION F.S. 4 F.S. 18 F.S. 41 to 58 Production Break F.S. 69

DESCRIPTION skin, framing, pressure bulkhead flanges it the windshield Y/" slant panel attach Joints at the tra- Jerse beam - cockpit area 7uselage skin under :he pilot/copilot window 3ulkhead, including the surrounding skin

INSPECT FOR Cracks Loose Internal fastener inspection cracks/ from cockpit corrosion _ area Numerous cracks Cracks, loose fasteners CO~ENTS Access for inspection through nose wheel well Outside surface (Ref:

DSBs407 &

858) Remove cockpit soundproofing paneling

INSPECTION TOOLS Visual (1) This area should receive Dye Penetrant frequent inspection.

Visual Magnifying glass Visual Visual lo-power glass develop ment -Jul

**REMARKS N**

(1) Particular attention should be given to this area.

(2) The stiffener angles crack in the attach holes F.S. 18.

(1) Cracks are located along the rivet lines and are difficult to detect.

(1) Cracks are located in the upper skin/frame areas and the lower frame fittings.

(2) Special repairs have been developed for this area.

### Page 27

FUSELAGE . STATION F.S. 4 to 69 F.S. 41 to 69 F.S. 69 F.S. 69 NOTE:

NOTEl.+ w* FUSELAGE STATIONS - DC-6/7 AIRCRAFT INSPECTIONS cI,'d 4lQ 'd v? N9.

**INSPECT FOR**

**COMMENTS INSPECTION TOOLS**

REMARKS Fc

DESCRIPTION Cockpit area - floor boards Nosewheel well. Nose gear trunnion Battery box cutouts, skin and lap joints (internal/external) Production joint attach angle Refer to Douglas Serv ce Bulletin Close and frequent at cockpit area.

Cracks/.

Corrosion Loose and working fastener cracks Cracks/ Corrosion Cracks ention shou Floor remove None Internal inspection 0 the frames and stringer 407 and 858 1 be given to Visual Visual Visual Visual Dr additional the under floe

(1) Check for corrugation cracks.

(2)*Check floor beams, frames stringers. (NOTE 1)

(1) Check for black residue around inner face of fitting and the rivets.

(2) Looseness of the trunnion fitting may result in nose gear shimmy.

(WIndications of corrosion can be found along edges of the skin lap, rivets along with pitted surfaces, blisters.

(2) Frequent cleaning treatment and protection necessary.

(1) Crack location in metal adjacent and inline with crew door.

nformation.

. cleanliness of the

### Page 28

**FUSELAGE**

STATION F.S. 69 to 134 F.S. 69 to 134 F.S. 69 to 134

DESCRIPTION Crew door Front crew door frame, and door hinges Front crew door hinge case FUSELAGE STATIONS - D&6/7 AIRCRAFT INSPECTIONS e* h)n

INSPECT FOR Rigging Cracks/ Corrosion Cracks CWNTS Critical Remove fuselage around door. frame None

INSPECTION TOOL Visual Dye Penetrant Visual Visual lo-power glass, Dye Penetrant

(1) Particular attention should be given to rigging of bayonets and rollers.

(2) Improper rigging results * in excessive wear, cracks, and pressurization leaks.

(1) Critical Area - Cracks are located in the aft section, upper section down midway of door.

Most critical point is located between stringer Nos. 10 and 11 approximately to 17" from floor line. Also, cracks occur in a lower corner of door sill. Area prone to severe corrosion.

(1) Crack location - hinge line. Area should receive close and frequent atten- g + tion. D'd %% 3 wrp: X

### Page 29

.

FUSELAGE STATIONS - D&6/7 AIRCRAFT INSPECTIONS w* P'd OQW

**FUSELAGE**

STATION F.S. 69 to 134 F.S. 69 to 134 F.S. 69 to 134 F.S. 89 to 100 F.S. 101 to 118 NOTE:

NOTE l.*

DESCRIPTION Intercostals below crew door Crew door Crew entrance door jamb Stringer No. 31 left and right sidefuselage Nosewheel well tunnel 1 'ypical repair instruc .igging of the crew dc Ixcessive wear, cracks

INSPECT FOR Cracks/ Corrosion Cracks/ wear Cracks Cracks/ Corrosion Cracks/ Corrosion :ions may be found in the )r bayonets, and pressur 1 CWMENTS (Ref: DSBs 407 & 858) None Remove lining above door (Ref: DSBs407 5c 858) rhorough cleaning prior to inspection nd rollers is .zation leaks,

INSPECTION TOOLS Visual and/c as required Visual Visual Dye Penetrar and X-ray X-ray and/or as required Visual SnufacturerQ rritical, In -

(1) Close and frequent attention should be given to this area.

(l)*Cracks start in the bayonet cutouts in the door intercostals.

(NOTE 1)

(1) Crack location No. 1 upper forward and No. 2 upper aft latch cutouts.

(2) Close and frequent inspections.

(1) Frequent and close attention should be given to this area.

(1) Crack location - aft lower corners.

nanua 1.

roper rigging results in

### Page 30

I

**FUSELAGE**

STATION F.S. 69 to 400 F.S. 134 to 179 5 F.S. 149

DESCRIPTION c* FUSELAGE STATIONS - DC- 6/7 AIRCRAFT INSPECTIONS tan *h) NO m I \Iu

**REMARKS N INSPECT FOR**

COMMENTS INSPECTION TOOLS Fuselage skin, longerons, frames (belly) Cargo door hinge cutouts Stringers Nos. 28 and 31 and frames Corrosion internal/ external Cracks Cracks _ .

Access to area through front lower baggage bin None Internal/ external (Ref DSBs 407 &

858) Visual X-ray Visual Visua 1 X-ray Dye Penetrant

(1) Corrosion located inner - and outer sides of fuselage skin longerons, frames, and skin laps.

(2) White deposits on edges of skin laps, around rivets, blisters in paint, pits are indications.

(3) Frequent cleaning and treatment necessary.

(1) Crack location - radius of the cutouts and skin panel.

(2) Routine inspection necessary.

(1) Cracks 2 to 7 inches found along right side stringer. w* w'd cmv

(2) Cracks are located in v bottom row of rivet in qz the skin cap. 3c F*

### Page 31

**FUSELAGE STATIONS - D&6/7 AIRCRAFT INSPECTIONS**

**FUSELAGE**

STATION F.S. 178 to 260 F.S. 186 F.S. 178 to 260 NOTE:

NOTE 1: *

DESCRIPTION Fuselage skin lap - longeron No. 26 Fuselage skin lap - longeron No. 31 Lavatory floor and floor beams Particular attention Typical repairs and rn(

INSPECT FOR Corrosion Loose fasteners Corrosion Corrosion hould be gi difications

COMMENTS (Ref: DSBs 407 ti 858) None (Ref: DSBs 407 IL 858) Critical en to inspectj nay be found j

INSPECTION TOOLS Visual and/or as required Visual and/or X-ray Visual * In of magnesia 1 the manufact

(1) Located at the skin lap just below the forward water tank service panel.

(2) Particular attention should be given to this area.

(1) Severe corrosion in this area.

(2) Particular attention should be given to this area.

(1) Corrosion located in the floor and floor beams.

Heavyespecially around the sink area. (NoTE 1)

(2) Inspection can be made from the forward lower baggage bins.

(3) Popped rivets and paint blisters are.external indicators.

L floor beams.

rer's manual.

### Page 32

**FUSELAGE STATIONS - DC-6/7 AIRCRAFT INSPECTIONS**

**FUSELAGE**

STATION F.S. 178 to 260 F.S. 241 to 280 F.S. 261 to 280 F.S. 301 NOTE: ?articular attention s louId be giv NOTE I:* Typical repairs and mc

DESCRIPTION Butt joint - hydrauli compartment Fuselage skin lap - stringers Nos. 19 through 23 Fuselage frames - cargo bin Fuselage - skin lap

INSPECT FOR Corrosion Cracks/ Corrosion crushed frames Crushed fuselage frames/ cracks Corrosion Hfications

COMMENTS (Ref: DSBs 407 6( 858) Critical Area covered by ice plates (Ref: DSBs 407 & 858) * Remove baggage bin floor and lining .

None n to inspectil lay be found i

INSPECTION TOOLS Visual X-ray Visual Visual Visual (Ref: DSBS 407 bc 858) n of magnesium the manufact

(l)*This condition is due to spillage from the lavatories. (NOTE 1) W*Close and frequent inspection should be made in this area.

(1) Frequent inspections should be accomplished in this area.

(1) None

(1) Corrosion located in the faying surfaces of the skin lap approximately 17" above the top of the first cabin window.

(2) Popped rivets, paint blisters, pitted areas . F$ indicators. %X 3 floor beams.

rer's manual.

### Page 33

**FUSELAGE**

STATION F.S. 341 F.S. 358 to 391.

F.S. 400 to 417 F.S. 400 to 512

DESCRIPTION Fuselage skin lap along stringer No. 26 Fuselage skin, longeron frames .

Fuselage skin Fuselage skin lap - stringer No. 19 .

FUSELAGE STATIONS - DC-6/7 AIRCRAFT INSPECTIONS w* NU %s 3 INSPECT COMMENTS INSPECTION REMARKS y FOR TOOLS 3c * Corrosion Corrosion/ Cracks Cracks/ Corrosion Corrosion None None Access throug wing fillet inspection plates. .

Remove fillet for thorough inspection.

(Ref: DSBs 407 & 858‘) (Ref: DSBs 407 & 858) Visual X-ray Visual.

X-ray .Visual X-ray Visual X-ray

(1) Severe corrosion located in the skin laps.

(1) Corrosion located just belowthe cabin window.

(2) Area should receive frequent attention.

(1) Cracks lodated in skin above the front spar cap and along the fioor line.

(2) Loose and popped rivets, paint and metal blisters are indicators of this condition.

(1) Corrosion extended over a 2-inch wide strip along stringer No. 19.

(2) Corrosion around and under the lower hinge fitting of the forward emergency exit at F.S. a+ 448, iw *, .O al h)

### Page 34

**FUSELAGE STATIONS - DC-6/7 AIRCRAFT INSPECTIONS**

**FUSELAGE**

STATION F.S. 500 F.S. 448 to 500 F.S. 280 4 to 600

DESCRIPTION Fuselage skin ?uselage longitudinal skin lap Zabin floor structure and supports

INSPECT FOR Cracks Cracks Cracks

COMMENTS (Ref: DSB

652) Inspect all exposed structure.

Remove soundproofing as necessary for access to front and rear spars.

(Ref: DSB 4 dr 567)

T INSPECTION TOOLS -~ Visual X-ray Dye Penetrant Visual Visual

(1) Cracks are located in the fastener holes in the fuselage skin at the wing to fuselage attach angle.

(2) Cracks also found in fuselage skin above rear spar.

(1) Cracks located in the skin lap above the first and second cabin windows right side.

(2) Crack le.ngth range up to 2” long.

(1) Place particular emphasis on inspection of fuselage, frames 413, 421, 460, and 5000

(2) Ref. to DSB 567 for information concerning floor to frame bracket. w* Q,'d

(3) Ref. DSB 611 and 651 for s 2 inspection of attach "tee" a k fittings. x I *

### Page 35

**I FUSELAGE**

STATION I F.S. 280 to 600 F.S. 280 to 600 NOTE: Re er to the manufacture1

DESCRIPTION Emergency exit cutouts Window frames FUSELAGE STATIONS - DC-6/7 AIRCRAFT INSPECTIONS

INSPECT FOR Cracks Corrosion Is manual ar

COMMENTS (Ref: DSBs 407 & 858) i service bull

INSPECTION TOOLS Visual Visual !tins for nece

**REMARKS**

(1) Cracks are located in the radius of the cutouts.

(2) A service bulletin was issued covering this area,

(3) Frequent attention should be given to this area.

(1) Intergrannular corrosion located in the lower corner of No. 8 window.

(2) Popped rivets, blisters in the skin, and paint are indicators.

(3) Check for presence of .

moisture in the insulation material. Ref.

DSB 840, sary repairs.

### Page 36

I .

**FUSELAGE**

STATION F.S. 280 to 600 F.S. 500 to 600 I F.S. 500 9 to 600

DESCRIPTION O”* FUSELAGE STATIONS - DC-6/7 AIRCRAFT INSPECTIONS ia *r\, NO m 4 \)ul Lavatory window Heater compartment, frames, longerons, floor beams Heater exhaust area longeron 24

INSPECT FOR Corrosion Corrosion/ Cracks Cracks/ Exhaust damage

CCMMENTS (Ref: DSBs 407 6 858) If blankets are installed,check for moisture (Ref: DSB

520)

INSPECTION TOOLS Visual Visual Visual co

**REMARKS**

(1) Corrosion can found between the fuselage skin and doubler at the lower edge of the cutout.

(2) Corrosion can become severe. Particular attention should be given to this area.

(3) Evidence of moisture in the insulating material should be checked.

(1) Cracks are located in the frames and longerons.

(2) Moderate to severe corrosion in the floor beams.

(1) Cracks and damage results from high heat exhaust temperatures.

(2) Modifications have been w* g $ developed. m!3 wa )-' )I)* X

### Page 37

_. . .

**FUSELAGE .**

STATION F.S. 500 to 600 F.S. 661 to 1194 F.S. 661 to 1194 1 NOTE: Re FUSELAGE STATIONS - DC-6/7 AIRCRAFT INSPECTIONS

DESCRIPTION Emergency exit doors Passenger entrance door frames, skin, floor, and buffet area Passenger entrance door hinge case er to the manufacture

INSPECT FOR Cracks Cracks/ Corrosion Cracks/ Corrosion Is manual fc

COMMENTS None (Ref: DSBs 407 & 858) Removal of buffet required for thorough inspection (Ref: DSBs 407 & 858) Y repairs and

INSPECTION TOOLS Visual Visual Dye Penetral X-ray Visual Dye Penetrar lodifications

(1) Cracks are located in the intercostal located immediately under the window. Cracks normally start in the angles.

(1) Moderate to heavy corrosion in the door sill panel.

(2) Corrosion in the buffet floor area can be severe.

(3) Frequent and close inspection of these areas recommended.

(1) Cracks are located at the front of the door frame,

(2) Fuselage skin cracks at the upper forward corner of the door hinge cutouts and both upper and lower hinges.

### Page 38

**FUSELAGE STATIONS - DC-6/7 AIRCRAFT INSPECTIONS**

**FUSELAGE**

STATION F.S. 661 to 1194 F.S. 661 to 1194 F.S. 10X to 1194 F.S. 103c to 1194 F.S. 103= to 1194

DESCRIPTION Rear pressure bulkhead Tail cone area Horizontal stabilizer stub. (center section Tail cone area Horizontal stabilizer stub. (center sectior

INSPECT FOR Cracks Corrosion Cracks Corrosion Cracks

COMMENTS Chonic Light/Medium None Light/Medium None

INSPECTION TOOLS Visual Dye Penetrant X-ray Visual Visual X-ray Visual Visual X-ray

(1) Cracks are located in the stringers and attach fittings at the pressure bulkhead,

(2) Frequent and close attention should be given to this area.

(1) This can be controlled by cleaning treatment and painting.

(2) Blisters and flaking of paint are indicators.

(1) Cracks are located in the skin attach points to the front and rear spar.

(1) This can be controlled by cleaning treatment and painting.

(2) Blisters and flaking of paint are indicators.

(1) Cracks are located in the skin attach points to the front and rear spar.

P

### Page 39

**EMPENNAGE**

STATION Sta. 70 to 130 Sta. 30 NOTE: X-

DESCRIPTION Horizontal stabilizer Horizontal stabilizer bay with steel bolts i rosion is difficult t . mtp P)d EMPENNAGE STATIONS - DC497 AIRCRAFT INSPECTIONS Yii! 3 rP1 INSPECT CWMENTS INSPECTION REMARKS =P + x FOR TOOLS Fc Loose Visual (lI'Lo&e rivets located fasteners Dye Penetran in the lower skin where (numerous) Magnifying it is attached to the Cracks glass front spar.

Cracked Cracks' are X-ray (1) Cracks are located in attach difficult the stabilizer attach fitting to locate. castings.

Critical

(2) Cracks usually start at the upper side of fitting which is covered by skin and progresses spanwise through the boltholes. .

stalled wil result in blt Iking out def :ts in aluminum.

detect by -ray if the pi rticles remai intact in the metal.

=b Ar) L A0 zcfn c\)

(3) Particular attention should be given to these fittings since the cracks do not progress from the outside where they could be detected visually or with dye penetrant.

### Page 40

**EMPENNAGE**

STATION Sta. 126, 202, and 252 Sta. 937 to 1115 Sta. 959 to 986

DESCRIPTION Elevators Rudder - torque tube Vertical stabilizers Vertical stabilizer DC-6/7 AIRCRAFT INSPECTIONS EMPENNAGE STATIONS -

**INSPECT COMMENTS INSPECTION**

FOR TOOLS Cracks None Wear/ None Visual (1) Excessive wear and Corrosion corrosion between the tube and the bearing seats.

Cracks Cracks and (Ref:* DSBs Visual (1) Cracks have been found loose bolts 723 A796 and X-ray on the lower left side of in the 796) Dye Penetrant the vertical stabilizer.

stabilizer RI* nose sectior DV (2) Particular attention op’d should be given to the (9 ra metal cap after lightning cn s’ strike report for burned * areas l Visual (Ref: DSBs 723 Visual (1) Cracks are located in 4796, and 796 X-ray the front fitting of the Dye Penetrant vertical stabilizer at the fuselage to vertical .

stabilizer attach point.

(1) Cracks located at the hinge cutouts on the elevator skin.

(2) This can result in in-f light vibratiori due to looseness in the fits between the tube and bearing seats.

I

### Page 42

**I WING**

**STATION**

w.s.-

0. -60 KS.

0-60 W.S.

O-60 W.S.

32 KS.

**32 , NOTE 1.**

DESCRIPTION Front upper spar csp Stringers, wing center section Center spar cap splices Front lower spar cap forward tang (extending thru fuselage) Front lower spar ceo aft tang (extending thru fuselage) * Cracks have develop operation due to ex w* WING STATIONS - DC-6/7 AIRCRAFT INSPECTIONS P

INSPECT FOR Cracks Cracks Cracks Cracks Cracks d exceeding limitations rt cting fits, wing angle, ar

COMMENTS (Ref. DSBs 406 do 857) Internal inspection access door Internal inspection access door Internal inspection access door' Internal inspection access door Internal inspection access door

INSPECTION TOOLS X-ray, Visual, Magnifying glass Dye Penetran X-ray, Visual, or Dye Penetran X-ray, Visual, or Dye Penetran Visual, Dye Penetran or X-ray Visual, Dye Penetran or. X-ray luiring spar 1 disassembly

**REMARKS**

(1) Particular attention should be given this area.

(2) -Crack length range up to 2" long.

(1) Cracks found along forward side of stringer.

(l)*Frequent and close attention should be given this area.

(NOTE 1)

(1) Routine inspection necessary.

(1) Located at the bulkhead lap to tang

(2) Particular attention should be given this area, eplacement. This is a complex required.

z$ mtd a: ra ra x u

### Page 43

**WING**

**STATION I W.S. 32 W.S.**

32 W.S.

32 W.S.

55 - 60 t KS.

55 - 60 NOTE: F

DESCRIPTION Center lower spar cap forward tang (extending thru fuselage) Center lower spar cap aft (extending thru fuselage) Wing stringers 17 & 26 at intersections with fuselage attach angles Center upper spar cap forward tang Center lower cap forward tang zfer to manufacturer r pair manual and service br -WING STATIONS - DC-6/7 AIRCRAFT INSPECTION WP D@d 09Q.

9 y COMMENTS LNSPECTION TOOLS REMARKS x ul INSPECT FOR Cracks Cracks Cracks Cracks Cracks None Internal inspection access door Internal inspection access door None Internal inspection access doors Visual, Dye Penetrant or X-ray Visual, Dye Penetrant or X-ray Visual or X-ray Visual or X-ray Visual or X-ray lletins for rt

(1) Routine inspection ' necessary.

(1) Located at bulkhead lap to tang.

(2) This area should receive frequent attention.

(1) Cracks found along forward side of stringer.

(2) Cracks located in forward line of rivets in spar 'cap.

(1) Cracks located inboard of attach angles.

(2) Place particular emphasis on this area.

(1) Cracks located in tang at skin lap.

(2) This area should be frequently inspected.

lair instructions.

### Page 44

**WING STATIONS - DC-6/7 AIRCRAFT INSPECTIONS WING**

**STATION W.S.**

55-60 W.S.

55-60 W.S.

60 KS.

60 W.S.

60 NOTE:

DESCRIPTION Center upper spar cap aft tang Center lower spar cap aft tang Inboard end of flap top nose section skin Nos. 2 & 3 fuel tank access doors Upper wing to fuselage attach angles efer to manufacturer

INSPECT FOR Cracks Cracks Cracks Cracks Outside surand popped face inspecrivets tion Cracks Internal inspection access door epair manua CQ9MENTS None None Outside surface inspection and service

INSPECTION TOOLS Visual or X-ray Visual or X-ray Visual, Magnifying glass Visual, Magnifying glass Visual, Dye Penetrant, X-ray Jlletins for

**REMARKS**

(1) Cracks located inboard of attach angle.

(2) Place special emphasis on inspection of cap at longeron 22. '

(1) Cracks located in tang at skin lap.

(2) Particular attention should be given this area.

(1) Cracks located along rivet lines and difficult to locate.

(1) Crack location - radius of cutouts and skin.

(2) Routine inspection necessary.

(1) Crack location - cracks in boltholes,

(2) Frequent inspections should F$ be accomplished in this area.% z 3 e'pair instructions. WE X u

### Page 45

**WING**

**STATION W.S.**

60 WA.

60 -65 KS.

60 -65 W.S.

67 W.S.

DESCRIPTION Front lower spar cap aft tang boltholes Front lower spar cap aft tang Front lower spar cap forward tang Wing stringer 22 inboard and outboard of this station Wing stringer 23 inboard and outboard of this station WING STATIONS - DC-6/7 AIRCRAFT INSPECTIONS w* @cd uQ)b 'ps COMMENTS REMARKS *rp: $4 INSPECT FOR INSPECTION TOOM Cracks Cracks Cracks Cracks Cracks Internal inspection access door Internal inspection access doors Internal inspection access doors Internal inspection access doors Internal inspection access doors VisuaLor X-ray Visual or X-ray Visual or X-ray Visual or X-ray Visual or X-ray .

(1) Crack location - horizontally between tang .

and spar cap.

(2) DSBs A678, 678, and 694 aPPlYi

(1) Cracks located at skin lap in tang.

(2) Routine inspection necessary.

(1) Cracks located horizontally between tang and. spar cap.

(2) Frequent inspection should be made of this area.

(1) Cracks located 'forward row of rivets.

(2) Close and frequent inspection necessary.

(1) Cracks start in forward row of rivets. Qcb lc3

(2) DSB issued on this area. Ph) Ao %k N

### Page 46

!

**I WING**

**STATION KS.**

60 W.S.

130.

W.S.

96 KS.

77 - 96 W.S.

i 133 - 163 a>+ WING STATIONS - DC-6/7 AIRCRAFT INSPECTIONS \n fu

DESCRIPTION Stringers at splices on lower wing plate Stringers 17, 18, 19, 20, and 21 Stringers 18, 19, and 20 Center spar web' inside wing fuel cell cavity Upper and lower spar caps in corner of nacelle spar area

INSPECT FOR Cracks Cracks Fatigue Cracks Cracks (Some .

cases 5" to 6" long) Cracks (fuel stains are telltale signs)

COMMENTS Internal inspection access doors (Ref: DSBs 406 & 857) Internal inspection access door (Ref: DSBs 406 & 857) Access between landing gear, drag strut, and main gear strut

INSPECTION TOOLS Visual or X-ray Visual or X-ray Visual X-ray Visual Magnifying glass Dye Penetranl Visual Dye Penetrati X-ray REMARKS xl ?a

(1) Refer to DSB 561.

(2) Cracks start in forward row of rivets. '

(1) Cracks have been found in both forward and rear rivet holes.

(2) Particular attention should be given this area.

(1) Crack location - forward row of rivets.

(2) Reference DSB 561.

(1) Cracks located vertically along web stiffener.

(2) Full cell liners must be removed for access to this area.

(1) Cracks radiate horizontally Fg from rivet holes. m'b Y ma (2) Particular attention should 5;' be given this area. cn

### Page 47

**1 WING**

**STATION I W.S.**

130 - 167 W.S.

122 W.S.

171 W.S.

114.5 W.S. t 148 NOTE: R

DESCRIPTION Top wing skin under nacelle fairing wing Center lower spar cap aft tang at three boltholes Center lower spar cap aft tang 'at three boltholes Center lower spar cap and wing skin from inboard side of No. 2 nacelle inboard to this W.S.

Center lower spar cap and wing skin from outboard side of NO, :

nacelle outboard to this W.S.

!fer to manufacturer% manua 1 and WING STATIONS - D&6/7 AIRCRAFT INSPECTIONS

INSPECT FOR Corrosion/ Cracks Cracks Cracks Cracks Cracks

COMMENTS Area susceptible to engine exhaust, gases, and vibration (Ref: DSBs 406 & 857) Internal inspection access door Internal inspection access door Internal inspection access door Internal inspection access door 2rvice bullet:

INSPECTION TOOLS Visual Visual or X-ray Visual or X-ray Visual or X-ray Visual or X-ray 1s for crack 1 -

**REMARKS**

(1) Reference DSB 762.

(2) This can be controlled by cleaning treatment and painting.

(3) Blisters and flakes of paint are indicators..

(1) Cracks radiate from boltholes.

(2) Routine inspection necessary.

(1) Cracks radiate horizontally, length of crack up to 3".

(1) Crack location - forward line of rivets.

(1) Crack location - forward and aft row of rivets.

(2) Cracks found in skin under spar.

2pair and corrosion treatment.

### Page 48

WING STATIO!

W.S.

114.5 KS.

148 W.S.

131 NOTE:

DESCRIPTION Center lower spar car and wing skin from inboard side of No. 3 nacelle inboard to this W.S.

Center lower spar caps and wing skin from outboard side of No. 3 nacelle outboard of this W.S.

Nos. 2 and 3 nacelle lower wing skin inboard of W.S. 167 outboard W.S. 131 .efer to manufacturer* reatment.

WING STATIONS - D&6/7 AIRCRAFT INSPECTIONS rn* '0 ra

INSPECT FOR Cracks Cracks Cracks/ Corrosion I manual and service bulle ins for crack repair and corrosion -

COMMENTS Internal inspection access door Internal inspection access door Internal inspection access door *N >O

**INSPECTION TOOLS .**

Visual or X-ray Visual or X-ray Visual or X-ray REMARKS Zen h)

(1) Crack length varies up to . 2" - 3 II l

(2) Usually located on front line of rivets.

(1) Crack location - forward and aft line of rivets.

(2) Routine inspection necessary.

(1) Moderate to severe corrosion.

(2) Cracks radiating from rivet holes., .

### Page 49

**WING**

**STATION W.S.**

131 KS.

131 I W.S.

167 - 282 NOTE: R

DESCRIPTION Splice or tie plates, landing gear, spar cap, lower front Center wing lower skin aft of center spar Aft and of main landing gear door assemblies Lower wing skin !fer to manufacturer% u* WING STATIONS - DC-b/7 AIRCRAFT INSPECTIONS P'd CJQTJ vi ma COMMENTS REMARKS P* 94 INSPECT FOR

INSPECTION TOOLS Cracks Cracks and Corrosion Cracks and Corrosion Small cracks and corrosion manual for :

Access thru wheel well Outside surface inspection Outside surface inspection (Ref: DSBs 406 & 857) tin repair ant Visual, Dye Penetrant X-ray Visual or X-ray Visual or X-ray Visual or X-ray corrosion .

trc

(1) Cracks located horizontally in lower cap where plates attach,

(2) Routine inspection necessary.

(1) Moderate to heavy corrosion.

(2) Frequent and close inspection of this area recommended.

(1) Moderate to light corrosion.

(2) Cracks radiating from aft row of rivets.

(1) Corrosion can become severe.

(2) Frequently inspect this area. r itment. '

### Page 50

**WING**

**STATION W.S.**

183 W.S.

203 - 282 W.S.

281 W.S.

281 KS, 242 NOTE:

DESCRIPTION Leading edge rib Stringers caps and crowns Wing skin and large fasteners Stringer tie ends Stringer No. 23 inboard/outboard of W.S.

,efer to manufacturer' .reatment.

DC-6/7 AIRCRAFT INSPECTIONS oo* WING STATIONS - AC3 L 10

**INSPECT FOR**

COMMENTS INSPECTION TOOLS REMARKS xl N Cracks Cracks inside and out, loose rivet Cracks Corrosion Cracks and loose rivets manual and (Ref: DSBs 406 & 857) None Outside surface inspection Access door Internal inspection access door ervice bullet ns for crack Visual or X-ray X-ray Visual Visual Visual or X-ray

(1) Routine inspection of this area.

(1) Cracks located in fastener holes.

(2) Crack length up to 2" long.

(1) Cracks located parallel to ribs. -

(2) Crack length up to 4" long.

(1) Moderate to heavy corrosion.

(2) Frequent inspections of this area.

(1) Particular attention should be given this area.

epair and corrosion 3 \oa P* x cn

### Page 51

m* WING STATIONS - DC-6/7 AIRCRAFT INSPECTIONS P'd cm@73 *!t WING

**STATION KS.**

242 KS.

130 - 167 300 - 336 W.S.

318 W.S.

1.49 - 318 W.S.

318 NOTE:

T Rc t:

DESCRIPTION Leading edge access door plate hinge, aft tang Frame of nacelle where attached to skin Wing skin behind outboard nacelle Wing skin under nacelle turtle back Supercharger mount , frames fer to manufacturer's eatment.

INSPECT FOR Corrosion .

and wear Cracks Corrosion (small pits) Cracks Cracks nanual and 1

COMMENTS Internal inspection access door Access thru inspection opening on nacelles Outside surface inspection Nacelle must be removed to locate cracks Access thru inspection door xvice bulleti rs for crack r

INSPECTION TOOLS Visual or X-ray Visual Visual X-ray Visual

(1) Corrosion is moderate to severe.

(2) Frequent cleaning treatment necessary.

(1) Nuisance cracks. .

(2) Routine inspection necessary.

(1) Corrosion is severe.

(2) Frequent cleaning is necessary.

(1) Cracks vary in length up to 2".

(2) Particular attention should be given this area.

(1) Transverse cracks have been reported.

(2) This area should be 00s given frequent inspections. Z0 *IQ -3 pair and corrosion %!n N

### Page 52

**I WING**

**STATION WA 281 KS, . 281 W.S.**

281 KS. .

281 1 KS.

293 NOTE: .efer to Douglas Service

DESCRIPTION Fuel tank sealants Wing skin Upper spar rail "Tee" angles Stringer No. 22 aft of center spar inboard/ outboard of KS.

. 00 WING STATIONS - DC-6/7 AIRCRAFT INSPECTIONS \* NO Fc -h) m0 COMMENTS REMARKS -1 u h) INSPECT FOR INSPECTION TOOLS Corrosion Cracks ant fuel leaks Corrosion Cracks Cracks ant loose rivets Bulletini Access door Outside surface inspection Access thru landing gear well Internal inspection access door Internal inspection access door Nos. 406 and Visual Visual or X-ray Visual or X-ray Visual or X-ray Visual or X-ray 157 for additi

(1) Corrosion found on wing skin when sealants removed.

(2) Frequent inspections of this area.

(1) Particular attention should be given this area. Consult manufacturer if repair not in repair manual.

(1) Corrosion light to moderate.

(2) Area should receive frequent attention.

(1) None

(1) Cracks are usually in forward line of rivets.

(2) Routine inspections necessary.

lnal information.

### Page 53

**WING STATIONS - DC-617 AIRCRAFT INSPECTIONS WING**

**STATION W.S.**

293 W.S.

242 KS.

300 - 336 W.S.

149 - 318 W.S.

149 NOTE:

DESCRIPTION Stringer No. 23 aft of center spar inboard/outboard of KS.

Stringer No. 22 inboard/outboard of W.S.

Nacelle former flange '(nacelle station 414) Nacelle to center spar attach gussets (nacelle station 460) Front spar cap forward lower tang at No. 3 inboard and outboard nacelle attach angle boltholes :er to manufacturer's m

INSPECT FOR Cracks and loose rivets Cracks and 'loose rivets Cracks Cracks Cracks nual and se

COMMENTS Internal inspection access door Internal inspection access door Access thru inspection plate Access thru inspection plate Access thru landing gear wheel well vice bulletin

INSPECTION TOOLS Visual or X-ray Visual or X-ray Visual Visual Visual or X-ray for repair i

(1) Crack location - on both forward and aft row of rivets.

(2) Check for loose rivets.

(1) Crack location - aft row of rivets.

(2) Length of cracks reported up to 2".

(1) Crack location - parallel to former. Area should receive close attention.

11) Cracks start in gussets and parallel to spar cap.

(2) Routine inspections necessary.

11) Cracks in tang found up to 4” long.

;tructions.

### Page 54

**WING**

**STATION W.S.**

318 W.S.

302 - 312 W.S. Fasteners inboard of 336 outboard nacelles 4 W.S.

339 NOTE:

DESCRIPTION Front spar cap forward lower tang at No. 4 inboard and outboard nacelle attach angle bolts Center lower spar cap forward tang at fuel sump cutout radius in cap inboar (W.S. 302) and outboard (W.S. 312) end of numbers 1 and 4 alternate tank sumps (bolts removed) Center spar upper rai 1 3fer to manufacturer' WING STATIONS - DC-6,7 AIRCRAFT INSPECTIONS oo* \n

INSPECT FOR Cracks Cracks Cracks Cracks repair manu

COMMENTS Access thru landing gear wheel well Access thru landing gear wheel well Outside surface inspection Access thru main landing gear whee 1 well .l and service

INSPECTION TOOLS Visual or X-ray Visual or X-ray Visual Visual X-ray bulletins for

(1) Cracks in tang radiate from rivet line.

(1) Cracks are located in fastener holes and also in wing skin.

(2) Crack length ranges up to. 2" long.

(1) Cracks radiate from fastener holes parallel to ribs.

(1) Cracks are located in the skin attach points.

(2) Routine inspection is necessary.

repair instructions.

### Page 55

**WING STATIONS - DC-6/7 AIRCRAFT INSPECTLONS WING**

**STATION KS.**

421 W.S.

336 W.S.

336 W.S.

378 W.S.

378 NOcrE: F

DESCRIPTION Stringer No. 26 hat sections and attach fittings Wing stringer No. 22 (outboard of this station) Wing stringer No. 23 (outboard of this station) Wing stringer No. 22 (inboard and outboard of this station) Wing stringer No. 23 (inboard and outboard of this station) zfer to manufacturer's

INSPECT FOR Cracks/ Corrosion Cracks/ Corrosion Cracks/ Corrosion Cracks/ Corrosion Cracks/ Corrosion repair manu

COMMENTS Access thru inspection door Access thru inspection door Access thru inspection door Access thru inspection door Access thru inspection door 1 and service bulletins for

INSPECTION TOOLS Visual (1) Corrosion moderate to X-ray heavy.

Visual X-ray Visual X-ray Visual X-ray Visual X-ray '

(2) Cleaning and painting will control.

(1) Corrosion moderate to heavy.

(2) Area should be frequently inspected.

(1) Corrosion moderate.

(2) Cracks parallel stringer longitudinally.

(1) Corrosion moderate.

(2) Cracks range up to 3" long.

(1) Corrosion light to moderate.

(2) Frequent inspections necessary.

repair information. .

### Page 56

. WING

**STATION KS.**

399 W.S.

399 W.S.

421 W.S.

421 W.S.

435 - 453 NOTE:

WING STATIONS - DC-6/7 AIRCRAFT INSPECTIONS e* NC,

DESCRIPTION Wing stringer NO. 22 (inboard and outboard of this station) Wing stringer No. 23 (inboard and outboard of this station) Inboard end of wing and lower and of attach fittings and stringers ltTee" clips at end of spars Upper wing skin at skin lap at front spar tefer to manufacturer's

INSPECT FOR Cracks/ Corrosion Cracks/ Corrosion Corrosion Cracks Cracks repair manu C@MENTS Access thru inspection door Access thru inspection door Internal inspection access door None Outside surface inspection 1 and service .

INSPECTION TOOLS Visual X-ray X-ray Visual Visual X-ray Visual xMetins for

(1) Severe corrosion reported.

(2) Cracks are longitudinal, crack length up to 3" long.

(1) Corrosion moderate to heavy.

(2) Cracks involve stress corrosion.

(1) Corrosion light to moderate,

(2) Sealant area must be inspected.

(1) None

(1) Cracks parallel rivet row@

(2) Routine inspection is necessary.

repair information.

### Page 57

**WING**

**STATION W.S.**

421 - 710 KS.

421 - 705 KS.

462 - 517 KS.

485 W.S.

60 - 710 NOTE:

i NOTE 1. * Fiber glass trailin!

DESCRIPTION Rib clips (90') Aileron well Aileron trim. tab hinge points Aileron bell crank Wing trailing edge skin, ribs, clips, and stringers efer to manufacturer';

nformation.

WP . WING STATIONS - DC-6/7 AIRCRAFT INSPECTIONS Pm YKii 3 I l-a REMARKS m r* x INSPECT FOR

COMMENTS INSPECTION TOOLS cn Cracks Small cracks Small cracks Cracks Nuisance cracks manuals ant edge will c Internal inspection access door Outside surface inspection Outside surface inspection Internal inspection access door Internal inspection and also on outside surface (Ref:

DSBs 406 6s

857) service bulle :ins tor repai !velop small c l acks in radiu Visual Visual Visual Visual Visual

(1) Cracks radiate from fastener holes on stringer and/or rib.,

(1) Routine inspection of this area.

(1) Particular attention .

should be given this area,

(l)*Failure have been reported due to wing gust loads on ground.

(See Note 1)

(1) These areas should receive frequent inspections.

and corrosion treatment oob at tip. (Maintenance item) \c3 L 10 m I NJW rQ

### Page 58

**WING**

**STATION KS.**

60 - 470 KS.

167 281 334 Wing flap links W.S. Wing flap support aft 167 boltholes W.S.

281 Spacer block/flap actuator NOTE 1.

DESCRIPTION Wing trailing edge and flap well area * Misalignment of linl impose large loads ( in cracking in this WING STATIONS - DC-6/7 AIRCRAFT INSPECTIONS O”P iv

INSPECT FOR Corrosion Cracks and Misalignment Oversize hole Improper clearance s will resu:

n brackets 1 5rea.

COMMENTS Outside surface inspection Outside surface inspection Service wear None Visual (1) None : in cracking lat are attach

INSPECTION TOOLS Visual Visual Visual :he link and a !d to the rear RIPlARKS rlul h>

(1) Corrosion moderate to heavy due to exhaust gases.

(2) Frequent and close inspection of these areas recommended.

(3) Frequent cleaning and treatment necessary.

(l)*Routine inspection of this area desirable. (See Note 1)

(1) Routine inspection of this area.

tach brackets. Also, it will Fg spar structure which can result % x 3 PCL \J b-J* 94

### Page 59

**WING**

**STATIONS W.S.**

421.

W.S.

63 421- NOTE: Rc WING STATIONS - DC-6/7 AIRCRAFT INSPECTIONS

DESCRIPTION Flap trailing edges Flap structure damage fer to manufacturer%

INSPECT FOR Warpage Cracked ribs, clip skin, and loose rivets repair manua

CCMMENTS Outside surface inspection None . and service

INSPECTION TOOLS Visual Visual julletins for

**REMARKS**

(1) Excessive warpage may cause flight control problem,

(2) Particular attention s,hould be given this area.

(1) Damage is usually caused during ground operation.

(2) This area should receive frequent inspections.

etailed repair instructions.

### Page 60

AC 20-52 Appendix 6 8/24/67 Page 1 APPENDIX 6.

1 . DC-6 AIRCRAFT MAINTENANCE INFORMATION. The following is a listing of significant maintenance difficulties that have been reported by air carriers as mechanical reliability reports from 1964 to 1967.

This information may be useful in identifying additional structural inspection areas:

a. Wings.

(1) During an overhaul inspection, the main landing gear outer cylinder, P/N 8065H2, was found cracked in the radius area of the outside diameter of the cylinder just below the "YO arms. . Repairs were accomplished in accordance with the manufacturer+ instructions. The- aircraft total time was 25,000 flight hours. This same condition was found on another aircraft having 31,000 flight hours. #

(2) Cracks were found in the trunnionbore of the left and right front spar main landing gear drag strut fitting. The drag strut fitting was replaced. The aircraft total time was 49,786 flight hours.

(3) During inspection, the right wing flap strut assembly link support, P/N 5329694, located at W.S. 167 was found cracked at the aft end. The flap support was replaced. Time since the last inspection was 509 hours.

(4) During landing, the left wing flap was damaged. Investigation revealed that the left outboard hinge bracket assembly, P/N 3365189, was broken. The bracket was replaced.

(5) A two-inch crack was found in the upper wing skin. The crack was located at W.S. 96, inboard of the No. 3 nacelle in the aft corner of the tank access hole. The aircraft total time was 25,208 hours. .

(6) During inspection, the right and left flap hinge fittings were found cracked in the inboard web at the radius of the hinge hanger cutout at W.S. 167. Hinge fittings, P/N 54922130 13 and -14 were replaced. Aircraft total time was 19,783 hours.

(7) During a basic service check, the left front spar drag fitting, P/N 5325648, was found to be cracked. The crack ran from the drag strut fitting cutout, inboard and parallel with the front spar, approximately two and one-half inches below the inboard lug. The crack was approximately three inches long. The total time on the aircraft was 30,609 flight hours. The manufacturer has issued rework instructions including repetitive inspections at 100-hour intervals.

### Page 61

Appendix 6

(8) A one-inch crack in the lower skin of the right wing was found during a periodic inspection. The crack was located at W.S. 185 and 16 inches behind the center spar. Total flight time on the aircraft was 45,987 flight hours. A repair can be found in the manufacturer% repair manual.

' (9) A one-inch chordwise crack was found in the upper inboard attach angle of number one nacelle where it is attached to the front tang of the center spar. Also, a one-inch crack was found in this same angle where it attaches to the aft tang of the center spar. Approved repairs were accomplished. The aircraft total time was 23,749 flight hours.

(10) During a block overhaul, the upper left wing skin was found to be cracked at station 130. The crack was located forward of the center spar tangs. The crack ran diagonally and was two inches long. No other discrepancies were noted in the sur- .

rounding structure.

(11) Two chordwise cracks were found in the right wing lower skin at the stringer and fittings located at station 281. Manufacturer has a service bulletin covering the repair in this area. The total time on the aircraft was 18,214 flight hours.

(12) A two-inch crack was detected during a visual inspection in the box beam. The crack was located in the lower side of the right center forward and of the box beam in the aft cargo compartment.

The repair for this area can be found in the manufacturer% structural repair manual. The total time on the aircraft was 47,045 flight hours.

(13) A crack was found in the inboard attach angle at the center spar bolt in No. 4 engine nacelle. This was repaired in accordance with the manufacturer's repair manual.

(14) During a visual and dye penetrant inspection, a one-half inch crack was found in the gyro-support bracket. The crack extended from the bracket hole to the edge of the spar at the forward tang of the lower front spar cap at station 4. A repair was made in accordance with the manufacturer's structural repair manual. The total time on the aircraft was 44,155 flight hours.

(15) Stringer No. 18, located at station 300, was found to be cracked. The repair was made in accordance with manufacturer% Service Bulletin No. 561. The total time on the aircraft was 23,725 flight hours.

### Page 62

AC 20-52 8/24/67 Appendix 6 Page 3

(16) A three-inch crack was found in the attach angle at the point where the wing is joined to the fuselage aft of the front spar. The repair was accomplished in accordance with an approved repair. The total time on the aircraft was 23,725 flight hours.

(17) During a basic service inspection, the bottom tang of the left wing front spar was found cracked at station 160.

, The repair was accomplished in accordance with the manufacturer's service bulletin.

(18) A crack was found in the wing attach angle doubler where the wing joins the fuselage at station 400. A repair can be found for this area in the manufacturer+ repair manual.

(19) During overhaul, spanwise stringer No. 23 on the lower wing surface was found cracked. The crack ran chordwise ' in the stringer crown and was located at W. S. 325.

The repair was accomplished in accordance with an approved repair method. Total time on the aircraft was 18,164 flight hours.

(20) The right wing lower skin was found to be cracked between the front and rear spars at W.S. 281, This repair was made in accordance with an approved repair method. Total time on the aircraft was 23,725 flight hours.

(21) Cracks were found in the left wing fuel tank access plate doublers 182b and 182~. Manufacturer's Service Bulletin No. 799 covers the repair of this area. Total time on the aircraft was 23,752 flight hours.

(22) During overhaul, the right-hand splice angle, P/N 42435221, on the nosewheel beam forward pressure bulkhead Gas broken, The attach angle was replaced with a new part. Total time on aircraft was 51,368 flight hours.

(23) The right center spar tang was found cracked at the bolthole outboard of the fuselage skin. Also, the attach angle was cracked at the same bolthole. This crack was approximately one inch in length. Manufacturer's Service Bulletin No. 678 covers the repair of this area. Total time on the aircraft was 48,958 flight hours.

(24, A four-inch crack was detected, by visual inspection, in the radius of the bottom vertical angle of the front spar at station @'O*'. The angle was replaced. Also, a two-inch crack was found in the front spar on the left side of the conduit hole located at station 28. A doubler was installed.

Total time on the aircraft was 47,112 flight hours.

### Page 63

AC 20-52 8124167

(25) A visual inspection revealed that the upper wing skin was heavily corroded in the area just forward of the rear spar at station 167. The section of wing skin was replaced.

Total time on the aircraft was 45,73? flight hours.

(26) During inspection, corrosion was noted on the doubler of the left wing trailing edge between stations 300 and 357.

A section of wing skin was removed that was 37 l/2 inches long and 10 3/4 inches wide. A repair for this area can be found in the manufacturer% repair manual.

(27) Inspection of the center lower spar cap revealed a crack that progressed fore and aft through the cap and upwards into the spar web approximately three inches. The crack was located in the left wing at W.S. 170 under the NO. 2 outboard lower fairing. Aircraft total time was 37,386 flight hours.

(28) During aircraft overhaul, the right main loading gear drag strut to the front spar fitting, P/N 5325648, was found.

cracked. The crack was located in the inboard brushing bore adjacent to the bore for the large trunnion nut.

Aircraft total time was 52,263 flight hours.

b a Fuselage.

(1)

(2)

(3)

(4) Inspection of the fuselage during a block overhaul revealed that the skin was cracked at the emergency exit cutout on the right side of the fuselage at station 557. The operator established an inspection of this area in its maintenance program to preclude further cracks. The total time on the aircraft was 23,749 flight hours.

During a block overhaul, the left ice plate was removed from F.S. 260. A one and one-half inch crack was found that was progressing vertically between stringers Nos. 21 and 22.

Also, a one-ix-&crack was progressing horizontally between stringers Nos. 22 and 23. The total time on the aircraft was 23,749 flight hours.

During a service inspection, cracks were found in the frame to foot fittings doubler at stations 497.5 and 498.5.

The repairs were accomplished in accordance with the manufacturer's recommendations.

The fuselage circumferential flange to the left stringer NO. 24 was found cracked at station 238L. The affected part of the flange was replaced.

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### Page 64

AC 20-52 8/24/67

(5)

(6)

(7)

(8) Appendix 6 Page 5 Corrosion was found around cabin windows 2, 3, 5, 7, 8, 9, and 10 on the left side of the fuselage and 4, 7, and 10 on the right side. The areas were cleaned, treated, and the metal replaced as required.

During overhaul, the upper fuselage attach angle was found cracked. Repairs were accomplished in accordance with the manufacturer% manual.

During an airworthiness directive compliance inspection, a transverse crack was found in the frame at F.S; 95.

The crack was located just above longeron No. 10. Repairs were made in accordance with the manufacturer's instructions.

Aircraft total time was 27,341 flight hours.

During overhaul, the wing skin to fuselage from attachment channel, P/N 5503731-l and -2, was found cracked.

The crack is located at F.S. 413 on the left side and ' it progressed through the upper inboard horizontal flange and vertical leg of the channel. The channels were replaced. Aircraft total time was 30,143 flight hours.

c. Stabilizers.

(1) During a periodic inspection, a fitting, P/N 4801674, was found cracked. The fitting is located on the right stabilizer at station 60. The combined length of the five short cracks was 6 l/8 inches. The fitting was replaced and continued inspection of this area is planned. The total time on the aircraft was 37,287 flight hours.

(2) During a periodic inspection, the right horizontal stabilizer attach fitting, P/N 4361674-1, was found to be cracked. This fitting is located at station 63 forward and on the top of the front spar. The fitting was replaced and inspection of this area will be continued at the periodic inspection period. The total time on the aircraft was 45,759 flight hours.

(3) The left horizontal stabilizer spar lower forward outboard fitting was found cracked. The fitting was replaced. Total time on the aircraft was 46,369 flight hours.

(4) During a service inspection, corrosion was found on the aft leg of the rear spar attach fitting, P/N 5361821, at the vertical stabilizer stub. The fitting was replaced.

Aircraft total time was 35, 071 flight hours.

### Page 65

Appendix 6 AC 200 52 Page 6 8124167

d. . Flight Controls.

(1) A ten-inch tear was found in the right-hand wing flap during a service ,check. This tear was located at station 415 and the tear was from inside out. The fairing at this station also had 10 rivets pulled loose. A repair was made in accordance with the operator% structural manual. Total time on the aircraft was 46,597 flight hours.

(2) A visual inspection revealed a cracked flap support, P/N 5329659. This was a complete.failure of the part. The location of the part is at the right W.S. 167. The flap support assembly was replaced. The total time on the aircraft was 47,418 flight hours.

(3) The right-hand flap hinge was found cracked at the forward outboard corner of the hinge fitting station 281 at the flap link cutout P/N FLA 1055. The flap assembly was replaced. '

(4) When the flaps were extended beyond 30 degrees, the aircraft would make a turn to the left. Inspection revealedthat the outboard flap linkage, P/N 5534780, was broken on the left wing flap: The link was replaced. Time since overhaul was 1,959 flight hours.

DC-7 AIRCRAFT MAINTENANCE INFORMATZON. The following is a listing of significant maintenance difficulties that have been reported by air carriers as mechanical reliability reports from 1964 to 1967. This information may be useful in identifying additional structural inspection areas:

a. Wings.

(1) Corrosion was found on the inner strut of the nose landing gear where it attaches to the fork. This was repaired by replacing the inner strut. Aircraft total time was 24,588 I flight hours.

(2) During.inspection, a two and one-half inch crack was found in frame P/N 5361581 at W.S. 50 between longeron 9 and 10 due to fatigue. Repairs were made in accordance with the manufacturer's instructions. AircrafttDtal time was 44,879 flight hours,

(3) A one and one-half inch crack was found in the upper wing skin during a routine inspection. The crack was located approximately two inches inboard of the No. 2 main fuel tank filler cap. Repairs were made in accordance with the manufacturer's instructions.

C- c- -

### Page 66

AC 20-52 8/24/67 * Appendix 6 Page 7 ( 1 4

(5)

(6)

(7)

(8) ( 9 1 During wing flap retraction, bolt P/N 2356375 failed in the link assembly P/N 4325008 at W.S. 378. The outboard flap shifted outboard riding on top of the right aileron holding it in the down position. The link assembly and flap were replaced. Aircraft total time was 20,030 flight hours.

During a routine service inspection, a one-inch crack was found in the wing to fuselage attach angle at station 381 on the right wing. Approved repairs were accomplished.

Total flight time on the aircraft was 22,621 flight hours.

The left outboard nacelle circumferential at station 400 was found cracked during aircraft overhaul. The crack was located at stringer No. 8 inside of the nacelle. A repair can be found in the manufacturer's repair manual.

The attach angle on the outboard side of number one nacelle ' found cracked at the leading edge of the wing. Also, the inboard top attach angle was cracked at the bolts on both sides of the center spar. Approved repairs were accomplished.

During overhaul, acrack was found on the outboard side of the No. 2 nacelle. This crack was located in the nacelle circumferential at station 384 in the "jr' box area. Approved repairs , were made in accordance with the manufacturer's repair manual.

During overhaul, the Nos. 2 and 3 main fuel tank doublers were found cracked at station 203. The manufacturers have a service bulletin covering the repair in this area.

(10) The fuselage attach angle doublers on top of the left and right wings were found cracked during aircraft overhaul. The cracks were located at KS. 40. This was repaired by replacing the attach angle doublers.

(11) During a routine heavy service inspection, the wing to fuselage attach doubler was found cracked af,t of the top forward spar attach fitting. The doubler was replaced. Also, L No. 3 top outboard nacelle attach angle was foundcracked in the angle radius. The crack was located approximately 12 inches forward of the front spar. A repair was made in accordance with the manufacturer's structural repair manual.

The total time on the aircraft was 20,143 flight hours.

(12) Inspection during a heavy service basic check period revealed that the nacelle to wing inboard attach angles in the NOS. 1 and 2 positions were cracked. The No. 1 attach angle contained a one and three-eighths of an inch chordwise crack slightly above th e angle bend radius. The No. 2 attach

### Page 67

Appendix 6 *, AC 20-52 angle was cracked between the rivets adjacent to the bend radius in a chordwise direction approximately one inch forward of the front spar. Also, it had a one and one-half of an inch crack in the aft end of the angle in the center of the bend radius directly over the rear spar. Both cracks were repaired in accordance with approved manufacturer's drawings. The total time on the aircraft was 19,345 flight hours.

(13) Inspection revealed-a three-sixteenth of an inch crack in the right top wing skin at the outboard aft corner of No. 3 alternate tank accessory plate cutout. Also the plate landing was cracked. The repair was acComplished by installing an outside doubler - 90-7075-56, on the skin crack and the accessory door landing was spliced. The total time on the aircraft was 15,597 flight hours.

(14) During a block overhaul, inspection revealed that the left .

wing skin was cracked from the center spar aft of the access cutout at KS. 203. The repair was made in accordance with the manufacturer% drawings. A special X-ray inspection of station 203 on the right and left wings of the fleet was conducted. The total time on the aircraft was 29,850 flight hours.

(15) During a special inspection, the following damage was found on the left wing: The upper wing skin was cracked at 16 places at station 167 between the front and center spars. The length of these cracks ranged from one-fourth of an inch to five inches long. Also, the upper wing skin was cracked threefourths of an inch at station 141 between wing stringers Nos.

. 6and7. In addition, the lower skin was cracked at station

167. This crack was six inches long and was progressing forwardfrom the rear spar. Repairs were accomplished in accordance with the manufacturer% recommendations.

(16) Special inspection of the wings disclosed the following damage:

The right upper wing skin was cracked in seven places between the front and center spars at station 167. The length of the cracks ranged from one-eighth of an inch to three and threeeighths inches long. The left upper wing skin was cracked in 16 places between the front and rear spars at station 167. The length of the cracks ranged from one-fourth of an inch to five and three-eighths inches long. The left upper wing skin was cracked at station 133 aft of the center spar. This crack was three-fourths of an inch long. Cracks three-fourths of an inch long were also found in the upper wing.skin at station 152 just aft of the center spar. In addition, seven cracks were found just aft of the center spar from station 132 to station 152.

These cracks were one-eighth to four and seven-eighths inches long. The repairs were made in accordance with the manufacturer's recommendations.

### Page 68

AC 20-52 8/24/67 Appendix 6 Page 9 b a Stabilizers.

(1) A nine-inch crack was detected during a routine inspection in the lower surface of the left stabilizer at station 107.

The aft end of the crack was located 12 inches from the rear edge of the stabilizer and its direction of progression was fore and aft through the row of rivets attaching the skin to the rib. The internal structure of the stabilizer was not affected. The repair was made in accordance with the structural repair manual.

c. Hydraulic Systems.

(1)

(2)

(3)

(4) Hydraulic fluid was lost when the flaps were extended during descent. Also, when the landing gear was extended, the pressure dropped to 900 p.s.i. Investigation of the aircraft after landing disclosed that the manual bypass valve was cracked at the fluid port. , The valve was replaced.

Hydraulic fluid and pressure were lost during taxiing resulting in the use of the airbrakes. Jnspection revealed that the inboard flap actuator on the left wing was leaking.

After takeoff, all hydraulic pressure and fluid were lost.

Inspection revealed that the manual bypass valve, P/N 340846601, had failed. The piston, P/N 2243941, failed at the lever attach end at the necked-down section in the 11/32-inch diameter area. The valve was replaced and the system operation was normal.

During taxi after completion of the landing roll, all hydraulic pressure and fluid were lost. Inspection revealed that the right inboard flap cylinder, P/N 3498899-1, was cracked. The flap cylinder was replaced and operation of the system was normal.

d . Landing Gear System.

(13 The landing gear was lowered for landing and the nose gear would not come down. However, after several attempts, it did come down and lock.' The aircraft was jacked,and on the retraction test, the gear would not move. Upon removal of the control valve, P/N 3480940-1, the *@up'* port was found .

to be blocked. Disassembly of the valve revealed that the port was blocked by soft solder. As a result of these findings, the hydraulic manifold was replaced and the system flushed.

### Page 69

Appendix 6 AC 20-52 8/24/67

e. Flight Controls.

(1)

(2)

(3) .

.During,routine inspection, the right wing..flap supports at station 281 and ths,right and left support‘s at station 372, ‘P/N 5498283-2 and 549834O"were found to.be corroded beyond specified limitations. Corrosion of the supports is considered to have resulted fromthe aircraft being in storage for seven months. The total time .on the aircraft was .

20,143 flight hours.

During overhaul, zyglo inspection of the elevator torque tube revealed that the right end attach fitting,P/N 3536439-3, was cracked. The crack was three-eighths of an inch long and extended from outboard through the bolthole. The defective part was replaced.

During a maintenance operation, a flap link assembly, P/N 549334, was found broken at the outboard end of the left flap. The failure occurred in the link-bearing area.

The total time on the aircraft was 22,249 flight hours.

f 0 Fuselage.

(11 The following discrepancies were noted during a routine 0 inspection: The left side of the fuselage skin was cracked in the rivets below the pilot's sliding window at station 41 The length of the cracks ranged from one-half to thiee-quarters of an inch. Eight cracks that ranged from a half to one and one-half inches in length were found in the skin below the pilot% window at station 22 between stringers Nos. 15 and 22. The fuselage skin was also cracked onthe left side at stringer No. 15 and F.S. 58.

The length of these cracks was one and one-half inches in length. In addition, cracks one and one-half inches in length, were found on the right side of the fuselage at stations 21 and 22. Repairs to these cracks were made in accordance with the manufacturer's structural repair manua 1. The total time on the'aircraft,was 22,621 flight hours.

(2) During a basic check period, the fuselage skin was found to have cracked beyond the stop drill hole at the left forward emergency exit upper hinge.. Repairs tiere accomplished in accordance with the manufacturer% structural repair manual.

The total time on the aircraft was 20,143 flight hours.

### Page 70

AC 2Q-52 8/24/67 Appendix 6 Page 11

(3) A two and one-half-inch crack was found inthe nose gear well web on the left side at station 58. The repair was accomplished in accordance with the manufacturer's structural repair manual. The total time on the aircraft Was 19,904 flight hours.

(4 9 . During the accomplishment of DSB 275, the fuselage formeic at F.S. 49.6 was found cracked. The crack was located between fuselage stringers Nos. 8 and 9 above the crew entry door. Aircraft total time was 28,225 flight hours.

### Page 72

AC 20-52 CHGl 7 Jul 72 Appendix 7 Page I 1 . Dc-6/-7 STRUCTURAL INSPECTION ITEMS.

a. Emergency Exit Door Hinges.

(1) Location. Fuselage emergency exits (see Figure G-3, Appendix 7).

(2) Applies to D&6/7 series aircraft.

(a) Action. All aircraft with emergency exit door hinges with less than a one-inch (1") door skin recess radius should have the hinges replaced. Applies to all models DC-6 series prior to serial number 44888 and DC-7 series up to serial number 44872 having 32,000 or more hours time in service.

(3) Other Reference Documents.

(a) DC-6 Service Bulletin 848. .

(b) DC-7 Service Bulletin 393.

(4) Probable Consequences. Failure of one hinge can cause failure of the second hinge resulting in loss of the emergency exit .

door,

(5) Recommendations. Periodic inspection, of hinges having l-inch door skin recess radius to assure continued structural integrity.

b l Emergency Exit Door Hinge Cutouts.

(1) Location. Fuselage Emergency Exits (see Figure G-4, Appendix 7).

(2) Applies to DC-6/7 series aircraft.

(3) Other Reference Documents.

(a) DC-6/*7 Advisory Circular20-52 Appendix 4, Page 10.

(b) DC-6 Service Bulletin 623.

(c) DC-7 Service Bulletin 79.

(4) Probable Consequences. Extension of fuselage cracks initiating at hinge radius could result in more extensive structural damage.

(5) Recommendations.

(a) Periodic inspections until the preventive rework of Service Bulletin l 623 or 79 is incorporated.

(b) Perform subsequent periodic inspections commencing at a later date to insure continued structural integrity after incorporation of Service Bulletin 623 or 79 preventive rework. .

### Page 73

Appendix 7 AC 20-52 CHG 1 7 Jul 72 ,

c. Crew and Cargo Door Area.

(1) Location. Forward fuselage, right hand side (See Figure G-5, Appendix 7).

(2) Applies to DC-6/7 series aircraft.

(a) Action. Periodic inspections of crew door jamb, adjacent skin, longerons, and nose to fuselage attach angles until . Service Bulletin 865 has been accomplished.

(3) Other Reference Documents.

(a) DC-6/-7 Advisory Circular 20-52 Appendix 4, Pages 3 and 4.

(b) DC-~ Service Bulletins 616, A636, 636, 731, 775, 788, 815, and 865,

(c) DC-7 Service Bulletins 182, A218, 218, 275, 316, and 417.

(4) Probable Consequences. Extensive fuselage cracks in this area may lead to more serious structural damage. .

(5) Recommendations.

(a) Periodic inspections should be continued until Service Bulletin 865 or 417 is incorporated.

(b) Periodic inspections should be continued after incofporatlon of the Service Bulletin 865 or 417 to assure continued structural integrity. c d 0 Vertical Stabilizer Front Spar-to-Fuselage Attach Fittings.

(1) Location. (See Figure G-6, Appendix 7)

(a) Fuselage Station 1033 (DC-6).

, (b) Fuselage Station 1073 (DC-7).

(2) Applies to DC-6 series aircraft.

(a) Action. Applies to all model DC-6 series aircraft prior to fuselage number 221 except 214.

1 If cracked beyond limits specified, the part should be replaced with improved fitting prior to next flight.

2 If original part is not replaced, inspection should be performed every 3500 hours.

3 DC-7 - None.

### Page 74

AC 20-52 CHG 1 7 Jul 72

(3) Other Reference Documents.

(a) DC-6/-7 Advisory Circular 20-52, Appendix 4, Page 15,

(b) DC-6 Service Bulletins 796 and A796.

(c) DC-7 Service Bulletin 407.

(4) Probable Consequences. Failure of fitting could result in a serious loss of structural integrity of the vertical stabilizer.

(5) Recommendations. Periodic inspection of original or improved fittings to assure continued structural integrity.

e. Main Entrance Door Area.

e (1) Location. Aft fuselage, left hand side (see Figure G-7, Appendix 7). ,

(2) Applies to DC-6/7 series aircraft.

(3) Other Reference Documents. .

(a) DC-6/-7 Advisory Circular 20-52, Appendix 4, page 12.

(b) DC-6 Service Bulletin 583.

(c) DC-7 Service Bulletins 317 and 400.

(4) Probable Consequences. Extensive cracking in this area could result in more serious structural damage. '

(5) Recommendations. Periodic inspections to assure continued strut tural integrity.

f . Fuselage Frames at Wing Upper Spar Cap Attach Area.

(1) Location. Wing-to-fuselage attach area (see Figure G-8, Appendix 7).

(2) Applies to DC-6/7 series aircraft.

(3) Other Reference Documents.

(a) DC-6/-7 Advisory Circular 20-52, Appendix 4, page 8.

(b) DC-~ Service Bulletins 611, 640, 652, and 789.

(c) DC-7 Service Bulletins 59 and 346.

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### Page 75

Appendix 7 AC 20-52 CHG 1 Page 4 7 Jul 72

(4) Probable Consequences. Continued cracking can result in a significant loss in strength of the wing‘to fuselage attachment.

(5) Recommendations. Periodic inspections to assure continued structural integrity.

8 0 Horizontal Stabilizer-to-Tail Stub Front Spar Attach Fittings.

(1) Location. Outboard end of horizontal stabilizer center section (see Figure G-9, Appendix 7).

(2) Applies to DC-6 series aircraft. .

(a) Action. Applies to following DC-6 aircraft: serial a numbers 42854 to 42894 inclusive, 43000 to 43012 inclusive:

43055, 43056, and 43062.

1 A 0.25 inch diameter stop hole should be drilled through t'he spar cap tang as crack stopper.

2 Periodic inspection is important when the stop drill hole is incorporated.

2 DC-7 (None).

(3) Other Reference, Documents.

(a) DC-6/-7 Advisory Circular 20-52, Appendix 6, Page 5.

(b) DC-6/-7 Advisory Circular 20-52, Appendix 4, Page 14.

(c) DC-6 Service Bulletin 831.

(d) DC-7 Service Bulletin 410.

(4) Probable Consequences. Continued cracking could significantly reduce the strength of the horizontal stabilizer spar joints.

(5) Recommendations. Periodic inspections to assure continued structural integrity.

h l Wing Lower Front and Lower Center Spar Caps at Wing Station 30.

(1) Location. Intersection of lower front and center spar caps and wing-to-fuselage attach angle (see Figure G-10 Appendix 7).

### Page 76

AC 20-52 CHG 1 Appendix 7 7 Jul 72 Page 5

(2) Applies to DC-6 series aircraft.

(a) Action. Applies to the following aircraft: DC-6A serial numbers 43296, 43297, 43817-43819, 43839-43841, 44063, 44064, 44069-44073, 44076, 44257. DC-6B serial numbers.

43257-43259, 43261043276, 43291, 43292, 43298-43300, 435180 43537, 43539043547, 43549-43555, 43557~43564, 43738-43741, 43743-43746, 43748~43750, 43820~43822, 43824~43826, 43828~ .

43834, 43836, 43837, 43842, 43844~43847, 44056-44062, 44080-44083, 44087-44089, 44102~44113, 44165-44168 and 44251, L If cracks are found, temporary or permanent repair should be made.

2 After permanent repair is incorporated, normal repetitive inspection should be made at intervals not to exceed 3,200 hours time in service. , 2 DC-7 - None.

(3) Other Reference Documents.

(a) DC-6/-7 Advisory Circular 20-52, Appendix 5, Page 1.

(b) DC-6 Service Bulletins A720, 720 and A821.

(4) Probable Consequences. Cracking of spar cap tangs could lead to more serious structural damage.

(5) Recommendations. Periodic inspections of this area to assure continued'structural integrity.

i . Wing Front, Center, and Rear Spar Caps at Station 60.

(1) Location. Upper and lower, front, center and rear spar cap tangs at station 60 bend area (see Figure G-11, Appendix 7).

(2) Applies to DC-6/7 series aircraft.

(a) Action. Applies to all N-6, DC-6A and DC-6B aircraft fuselage number 1 up to and including fuselage number 722 having an excess of 9000 hours in service and to all DC-7 and DC-7B aircraft fuselage number 1 up to and .

including fuselage number 720 having in excess of 8000 hours time in service.

1 Temporary or permanent repair should be made if cracks are .

found.

2 Periodic inspections should be performed if permanent repair is not incorpora ted.

### Page 77

Appendix 7 AC 20-52 CHG 1 Page 6 7 Jul 72

(3) Other Reference Documents.

(a) ~~-6/-7 Advisory Circular 20-52, Appendix 5, Pages 3 and 6.

(b) DC-~ Service Bulletins A678, 678, 694, 763, 824, and 857.

(c) . DC-7 Service Bulletins 167 and 406.

(4) Probable Consequences. Chordwise cracks in spar caps could result in failures in adjacent wing skins and stringers, causing a serious loss of structural integrity.

(5) Recommendations.. Periodic inspections after incorporation of respective reworks.

je Lower Front Spar Cap Splice at Main Landing Gear Drag Attach Brace Fittinq. .

(1) Location. Wing stations 131 and 167 front spar lower cap aft tang and splice plates (see Figure G-12, Appendix 7).

(2) Applies to DC16 series aircraft.

(a) Action. Applies to all models DC-6, DC-6A and DC-6B aircraft .

serial number 42854 up to.and including serial number 44429.

1 A rework should be performed if cracks exist.

2 Inspection should be made for preloaded flanges.

2 DC-7 - None.

(3) Other Reference Documents.

(a) DC-6/-7 Advisory Circular 20-52, Appendix 5, Page 8.

(b) DC-6 Service Bulletins 532, 749, 802, and 862.

(c) DC-7 Service Bulletins 345 and 414.

(4) Probable Consequences. Cracking in this area could reduce load carrying capability front spar splices.

(5) Recommendations. Periodic inspections to assure continued structural integrity.

k 0 Lower Center Spar Cap Splice at Wing Station 0.

(1) Location. Wing Station 0 (see Figure G-13, Appendix 7). '

(2) Applies to DC-6/7 series aircraft.

### Page 78

AC 20-52 CHG 1 Appendix 7 7 Jul 72 Page 7. (and 8)

(3) Other Reference Documents.

(a) DC-6/-7 Advisory Circular 20-52, Appendix 5, Page 1.

(b) DC-6 Service Bulletin 854.

(4) Probable Consequences. Continued cracking of center spar lower cap could result in more extensive structural lower panel.

damage to the wing

(5) Recommendations. Periodic inspections to assure continued structural integrity.

### Page 80

.

_ (6) VERTICAL STABILIZER FROiJT SPNI-TO-FUSEl&E (6) VERTICAL STABILIZER fR()iJT SPAR-TO-FUSE~GE ATTACH FITTINGS (Page 14) ATTACH FITTINGS (Page 14)

(3) (3) EHERGENCY EXIT DOOR HINGES (Page l ll) ’ EHERGENCY EXIT DOOR HINGES (Page l ll) ’

(4) EftEfXENCY EXIT DOOR HINGE CUTOUT (Page 12) (4) EftERGENCY EXIT DOOR HINGE CUTOUT (Page 12)

(5)CRfW rfid ,CARGO DOOR (5)CRfW rfid ,CARGO ODOR AREA (Page 13) AREA (Page 13) ‘-‘:;I-:

/\ ~lgoo33 ~lgoo33 tm .d I ; 1..

DOOR MA (Page 15) DOoR MA (Page 15)

(8) FUSELAGE'FRAKES AT WING UPPER (8) FUSELAGE'FRAKES AT WING UPPER SPAR CAP ATTACH AREA (Page 16) SPAR CAP ATTACH AREA (Page 16) L (9) t!ORIZOtlTAL STACILIZER-TO-TAIL

STUB FRONT SPAR ATTACH FITTINGS (Page 17) DC-6/-7 FUSELAGE/EWENNAGE STRUCTURAL INSPECTION ITEMS

### Page 81

.

LOWER CENTER SPAR CAP SPLICE AT WING STA. 0 (Page 21)

(11) WING FRONT CENTER AND REAR SPAR CAPS AT STATION 60 (Page 19)

(10) WING LONER FRONT AND

LOUER CENTER SPAR CAPS 1( (12) ;;$Rs;;;;; AT M L G\ AT WING STA. 30 (Page 18) DRAG BRKE ATTACil t IiTIiG- (Page 20) DC-6/-7 CENTER WIflG STRUCT'iRAL INSPCCTIOM LOCATIONS

### Page 82

AC 20-52 CHG 1 Appendix 7 7 Jul 72 Page 11 FIGURE G-3. EMERGENCY EXIT DOOR HINGES B B , VIEW A EMERGENCY EXIT’ DOOR

HINGE FITTING IHSPECT DOOR SKIN RECESS 1” RADIUS VIEW B-B .

### Page 83

Appendix 7 AC 20-52 CHG 1 7 Jul 72 FIGURE G-4. EMERGENCY EXIT HINGE CUTOUTS

**VIEW A EMERGENCY EXIT DOOR**

### Page 84

AC 20-52 CHG 1 Appendix 7 7 Jul 72 Page 13 FIGURE G-5. CW AND CARGO DOOR AREA @l’YP. CRACK LOCATIONS i” TYP. CRACK L I ’

VIEW B-B VIEW A (VIEhI LOOKIHG INBD & AFT)

**IIISPECT HINGE CASE AND HINGE CUTOUT SECTION C-C (ATTACH AMLES)**

INSPECT RADII AND AROUND FASTENER HOLES BETlaJEEN LOi’G. 11 IUD 17

### Page 85

\I \I N R N 0 i

### Page 86

AC 20-52 CHG 1 7 Jul 72 Appendix 7 Page 15 FIGURE G-7. MAIN ENTRANCE DOOR AREA INSPECT SKI14 AT RADIUS CUTOUT--, (DC-G) STA. 661 (DC-G) S-M. 7i:l-I (DC-7) STA. 701 (X-7) SX, 741 22 .

RACK LOCATICM 6 /\- TYPIC nf nL rno cm run Jl?\. 7m IV I -- -- -- VIEW A (VIEW LOOKII:G 111bD & AFT) IMSPET.T~E CASE MD HIIIGE CUTOUT .

### Page 87

m

### Page 88

.

AC 20-52 CHG 1 7 Jul 72 Appendix 7 Page 17 FIGURE G-9. HORIZONTAL STABILIZER-TO-TAIL STUB FRONT SPAR ATTACH FITTING TYP. C RAC REAR SPA; R STUB

ACCESS PANEL STA. 48.8 STA.62 -T- -- --- ir STA.77 FROiJT SPAR - A --- . A A HORI ZO?ITAL ST/X ILIZER-TO-TAIL STUI; KX-.i: - -- - / /- TYP. CRACK LOCATIOM c

**VIEW A-A - OUTUD**

**TYPICAL FOR UPPER AXI LONER FITTINGS**

### Page 89

W

### Page 90

c Y

### Page 91



### Page 92

AC 2042 CHG 1 7 Jul 72 FIGURE G-13. LOWER CENTER SPAR CAP SPLICE AT STATION 0 Appendix 7 Page 21

CENTERL I NE AIRPLAilE

VIEW A-A LOWER &iii-iiiR CAP I

**I I , I UP 1 I AFT**

SECTION B-B (TYPICAL) * U.;%VERIIYENT PRIIITMG OFFICE: 1979 -627-473/1838

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