Federal Aviation Agency
SAL AVIATION ROO DVSORY
CIRCULAR
TO PATES OF ARE
MAINTENANCE INSPECTION NOTES FOR DOUGLAS DC-6/7 SERIES AIRCRAFT AUGUST 24, 1967
DEPARTMENT OF TRANSPORATION Federal Aviation Administration AC NO: AC 20-52 Consolidated reprint:
January 1974 - includes Change 1
Federal Aviation Agency AC NO: AC 20-52
SAL AVAION AGE AIRCRAFT
ADVISORY CIRCULAR EFFECTIVE :
VITED SPATES OF AMERI 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. HOW TO GET THIS PUBLICATION.
a. Order additional copies of this publication from:
Department of Transportation Federal Aviation Administration Distribution Unit, HQ-438 Washington, D.C. 20 590
b. Identify this publication as: Advisory Circular 20-52, Maintenance Inspection Notes for Douglas DC-6/7 Series Aircraft.
ely rector Flight Standards Service
AC 20-52 CHG 1 Page i 8/24/67
TABLE OF CONTENTS Page No.
1. Introduction.
2. Description. 1
3. Background. 1
4. General Information. 1
5. Type of Construction.
General Inspection Tips.
Nondestructive Testing (NDT). 4 APPENDIX 1 STATION CHARTS (2 pages) Figure A-1 a. Outer wing and aileron. 1
b. Center wing flap.
c. Fuselage station.
Figure A-2 a. Vertical stabilizer and rudder. 2 °
b. Horizontal stabilizer and elevator.
APPENDIX 2 FUSELAGE COMPONENTS (5 pages) Figure B-1 Fuselage Major Components. 1 Figure B-2 Nose Section Assembly Floor Beam 2 Structure, Slant Panel Structure, and Slant Panel Skin.
Figure B-3 Lower Center Section Assembly Center Wing Section.
Figure B-4 Lower Center Section Assembly 4 Floor Beams (Stations 412 to 500) Figure B-5 Fuselage Floor Panels. 5 APPENDIX 3 CENTER WING SECTION (5 pages) Figure C-1 Center Wing Section Spars.
Figure C-2 Lower Center Section Assembly, Center Wing Section Structure.
Figure C-3 Center Wing Trailing Edge Fuel 3 Tank Spars Corrosion Resistant Seals.
Figure C-4 Flap Hinge Bracket and Linkage. 4 Figure C-5 Outer Wing Panel Attach Point. 5 APPENDIX 4 FUSELAGE STATIONS (15 pages) 1 APPENDIX 5 WING STATIONS (18 pages) 1 APPENDIX 6 DC-6/7 MAINTENANCE INFORMATION (11 pages) 1
AC 20-S2 CHG 1 Page ii / Jul 72 Page No.
* APPENDIX 7 DC-6/7 STRUCTURAL INSPECTION ITEMS (21 pages) Figure G-1 DC-6/7 Fuselage/Empennage. 9 Figure G-2 DC-6/7 Center Wing. 10 Figure G-3 Emergency Exit Door Hinges. 11 Figure G-4 Emergency Exit Hinge Cutouts. 12 Figure G-5 Crew and Cargo Door Area. 13 Figure G-6 Vertical Stabilizer Front Spar to Last Tre ling per are con 14 Figure G-/ Main Entrance Door Area. 15 Figure G-8 Attach Area. 16 Figure G-9 Horizontal Stabilizer-to-Tail Stub Front Spar Attach Fitting. 17 Figure G-10 Wing Lower Front and Lower Center Spar Caps at Wing Station 30. 18 Figure G-11 Wing Front, Center, and Rear Spar Caps at Station 60. 19 Figure G-12 Lower Front Spar Cap Splice at M.L.G. Drag Brace Attach Fitting. 20 Figure G-13 Lower Center Spar Cap Splice at Station O. 21 *
AC 20- 52 Page 1 8/24/67
1. 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 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. DESCRIPTION. The circular contains guidance material for performing 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..
3. BACKGROUND.
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. 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 knowledge of all the problem areas of the aircraft.
4• 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 DC-6/7 aircraft. Service Bulletins 406, 407 (DC-7), 857, and 858 (DC-6) 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 2 AC 20-52 8/24/67 manufacturer's recommendations and make certain that responsible maintenance personnel are knowledgeable on the subject.
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.
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.
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 consists of wing 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).
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.
The fuselage group is an aluminum alloy, semi-monocoque type structure, constructed of longitudinal stiffeners, transverse frames and bulkhead, and flush-riveted stressed skin. The fuselage is divided into three main sections - the nose section, upper and lower center section, and tail section assemblies.
6. GENERAL INSPECTION TIPS.
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 the wing and fuselage. External indications of failure, such as distorted skin, tilted or sheared relent to ted, raceter otto, kar are usually obvious.
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
AC 20-52 Page 3 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. 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 VERTICAL
CENTER SPAR CAPS TO FUSELAGE STABILIZER
BULKHEAD -FITTINGS
HORIZONTAL
STABILIZER
TIP ASSEMBLY
PASSENGER, CARGO and CREW DOOR AREAS,
FUSELAGE NOSE SKIN HINGE CUTOUTS 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.
Corrosion Prone Areas. Figure 2 refers to some of the corrosion prone areas in the aircraft. Manufacturer's service bulletins and manuals have been issued to provide detailed repair instructions.
Par 6
Page 4 AC 20-52 8/24/67 -GALLEYS WHEEL •PASSENGER, CARGO WELLS • LAVATORIES and CREW DOORS and CABIN FLOOR EXHAUST PATH AREAS LANDING GEAR and SUPPORTS 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.
NONDESTRUCTIVE TESTING (NDT).
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 interthe 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
AC 20-52 Page 5 8/24/67
AIRCRAFT STATION DIAGRAMS The wing, fuselage, and empennage station diagrams included in this document were developed for the DC-6B aircraft and are used 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.
421 19/72/8 23 23 30 FIGURE A-1. STATION CHARTS
FUSELAGE
LONGERONS INSPECTION 220
REFERENCE ONLY 13612 30 22/24 705 NOTE 727 2 178
FLAP STATIONS SAME AS
THE WING, ONLY HINGE POINT STATIONS SHOWN.
710 NOTE: AILERON STATIONS 421 SHOWN AT HINGE POINTS - 45
STATIONS OUTER WING & ALERON STATIONS CENTER WING & PLAP STATIONS FUSELAGE
INSPECTION ILLUSTRATIONS INSPECTION ALUSTRATIONS INSPECTION RIUSTRATIONS DC-6 DC-6 FIGURE A-1 DC-6A/B TA 69 (DC-7) similor to STA 29 (DC-7C) Appendix 1 STATION CHARTS (SHEET 1 OF 2)