AC NO: 20-78 DATE: 11 July 72
ADVISORY
CIRCULAR MAINTENANCE INSPEC!I!ION NOTES FOR McDONNESSCI DOUGLAS DC-8 SERIES AIRCRAFT
DEPARTMENT OF TRANSPORTATION
FEDERAL AVIATION ADMINISTRATION
AI: NO: 20-78 8 DATE. 11 July 72
ADVISORY
CIRCULAR
DEPARTMENT OF TRANSPORTATION FEDERAL AVIATION ADM~INISTRAJION SUBJECT: MAINTENANCE INSPECTION NOTES FORMcDONNELL DOUGZAS DC-8 SERIES AIRCRAFT 1 0 PURPOSE0 This handbook provides maintenance inspection notes which can be used for the maintenance support program for certain structural parts of the DC-8 series aircraft, 2 0 REFERENCESe a@ FAA Advisor.y Circular 20-50, Ultrasonic Testing January 1967, b 0 FAA Advisory Circular 20-61, Nondestructive *Testing for Aircraft, May 1968.
C. FAA Advisory Circular 65-9, Airframe and Powerplant. Mechanics General Handbook 1970.
d 0 FAA Advisory Circular 65-12, Airframe and Powerplant Mechanics Powerplant Handbook 1971,
e. Douglas Service Magazine, Volume XXIII, Issue No. 2 1965, f 0 Douglas Service Magazine, Volume XXIV, 1966.
3 0 DESCRIPTION. Maintenance inspection matters on the wing and fuselage are reviewed with a view toward supplementing information currently available, 4 0 HOW TO GET THIS PUBLICATION.
a, Order additional copies of this publication from:
Department of Transportation Distribution Unit. TAD0484~3 Washington, D,C, 20591 I ni ti ated by: FS-303A
Y
AC 20-78 11 July 72 TABLE OF CON!L'EN!L'S Page No.
CHAPTER 1. MAINTENANCE INSPECTION NmES. 1 1 l 2 l 3 l 4 l 5 0 6 l 7 0 8 l 9 .
10 0 CHAPTER 2.
Introduction.
Description.
Background.
General Information.
Tsrpe of Construction.
General Visual Inspection Tips.
Nondestructive Testing (NDT).
Aircraft Station Diagrams.
Definitions.
JXbbreviations Used In This Document.
1 1 1 2 2 4 4 4 5 5 WING. 7 11 l DC-8 Aircraft Maintenance Inf'ormation. 7 CHAPTER 3.. FUSELAGE. 11 DC-8 Aircraft Maintenance Information. I2 l 11 cm 4. FLIGHT CONTROLS. 13 DC-8 Aircraft Maintenance Information. 13 13 l cHAl?TER 5. LANDING GEAR. 15 14 0 DC-8 Aircraft Maintenance Information. 15 CHAPTER 6. FYLONS/NACELL~ l DC-~ Aircraft Maintenance Information.
1’1 1’1 15 l CHAPTER 7. STABILIZERS.
16 0 DC-8 Aircraft Maintenance Information.
CHAPTER 8. MIscELLANEaJs.
17 0 DC-8 Aircraft Maintenance Information.
19 19 21 21 Page iii
AC 20-78 CHAETm
APPEXDIX
APPENDIX Figure Figure Figwe Figure Figure Figure AH?ENDIx Figure Figure Figure Figure Figure Figure 9 l 18 l 19 l 20 l 21 0 22 0 23 l 24 0 25 l 26 0 27 0 28 0 29 l 30 0 31 l 10 l 32 l 1 l 2 l 1 l 2 l 3 l 4 l 5 0 6 0 3 0 7 0 8 l 9 0 10 0 11 0 12 l CORROSION PRONE ARE&S.
General.
Exhaust Trail Areas.
Engine Front&l Areas and Cooling Air Vents.
Battery Areas and Vents.
Lavatories, Galleys, and Cabin Floors.
Wheel Wells and Landing Gears.
Control Surface Recesses.
Spot-Welded Skins.
Hinges, 11 July 72 Page No.
23 .
23 23 23 23 23 24 24 24 24 Lap Joints Between ~uminum Ektruded Sections. 25 Fluid Entrapment Areas. 25 Electronic P&&age Compartments., 25 Control cables. 26 Micrdbiological Fuel Contamination and Corrosion.26 MAINTEZ0UKEINF'ORMATION. ' 27 27 1 1 DC-~ Aircraft eintenance Itiormtion.
DEXXCPTION OF STATIONS. (3 pages) STATION CHARTS. (6 pages) Basic Dimensions.
Fuselage Station Charts.
Wing Station Charts.
Pylon/Nacelle Station Charts.
Horizontal Stabilizer Station Charts.
Vertical Stabilizer Station charts.
1 2 3 4 5 6 0 1 STRUCTURAL ITEMS. (8 pages) DC-~ Aircraft Significant Structural Item.
Fuselage Aft Pressure Bulkhead.
Freon Compressor Exhaust Door Opening.
Forward Passenger Door Area Aft Passenger Door Area.
Aft Lower Wing Skin at Centerline Splice, Page iv
11 July 72 AC 20-78 CHAPTER 1. MAINTEZANCE INSPECTION 1 l IN!TRODUCTION. This advisory circular provides - NO!I!ES mainteriance 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 the McDonnell Douglas DC-~ series of airplanes. The material is based, in part, upon information made available through discussions with personnel who have maintained these types of airplanes for thousands of hours of tim 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. This circular contains guidance material for performing inspection and maintenance on wings, fuselage, empennage, flight controls, pylons/nacelles, and landing gear structures. The information has been derived from service experience. It does not comprise a full and complete maintenance program for the subSect aircraft but should be considered as supple=ntal mintenance data. Included in the circular are diagrammatic sketches and station identifications of the wing, fuselage, and flight controls.
In addition, there is a listing of selected maintenance difficulties which were reported during 1970 and 1971. Appendix 3 contains special structural items which are remmended for rework and/or periodic.
inspection to assure continued structural integrity of high tW DC-~ aircraft.
3 0 BACKERCXJND.
a, b 0 Aircraft Use. The Administrator 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 and airworthy condition.
Maintenance "Kjnow HOW/' Since maintenance *know how" is not trans ferred with the aircraft, the new operator generally goes through a learning cycle before he is able to rapidly pinpoint the 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 can also serve as a guide to other operators who have not accumulated sufficient experience to have knowledge of all the prdblem areas of the aircraft.
-PI Par 1 m3e 1
AC 20-78 11 July 72
a.
b 0 C.
Manufacturer% Bulletins. It must be emphasized that the manufacturer has mlished several service bulletins concerning the inspection, repair, and modification of McDonnell Douglas DCa8 series aircraft. Service bulletins highlight the importance of maintaining structural integrity on aircraft; with particular reference to areas known to have experienced crack and corrosion da=ge. Operators are urged to become conversant with the manufacturer's recmndations and make certain that responsible b maintenance personnel are lmowedgeable on this subject.
Airworthiness Directives. It is emphasized that the material in this circular does not supersede any of the requirenrents of airworthiness directives issued under Part 39 of the Federal Aviation Regulations.
Certification Basis. The United States type certificate holder is McDonnell Douglas Corporation, Long Beach, California. The basic design and first production airplane ww the DC-~-U. Model approved for transport category by the FAA on August 8, 199.
The Type Certificate Data Sheet No. 4A25 prescribes conditions and li&tations for which the type certbficate was issued.
However, the data sheet may be revised from tim to time as conditions and limitations change, Thus, it is important that the latest data sheet revision be available whenever a problem arises that may be covered in the data sheet. Twenty-one models of the DC-8 have been manufactured, the basic being the DC-8-U.
and the latest being the DC-8-63F.
5 0 !LTPE OF CQNS!l?RUCTION. The major structural components of the aircraft are the wing group, the fuselage group, and the tail group. The pr3mary structure, consists of the fuselage, pylons> wing, and the vertical and horizontal stabilizers. These components have been designed in accordance with the "fail safe" policy. This policy provides multiple load paths and reduced stress levels, such that a single failure of any structural elemnt will not result in the loss of the complete structural component, Several flap system components mset the *'safe life" reqgirements and the life limits for these parts are listed in Note 3 of Type Certificate Data Sheet No. 4A25.
a. The wing is an all-nretal, full cantilever-type structure and consists of a center section which extends from the airplane centerline to the dihedral and sweep;back at station X&9.5, the inboard section extending from the sweepback to station X&8, and the outboard section from station X&o8 to the wing tip. The primary structure consists of three spars, ribs, bul&eads, and pane-g of multiple stringers and stressed plating. The areas between the front and rear spars are used as integral fuel tanks.
The wing has four high lift leading edge slots and provisions are Page 2 WPl Par 4
11 July 72 AC 20-78 incorporated in the structure for attachmnt of flaps, spoilers, and ailerons. The leading edge and tips are the only portions not permanently joined to the wing structure; all other portions are not disassexibled except for major repair of primary structure.
b 0 T is an all metal structure composed of stressed aluminum alloy skin attached to transverse frames and longitudinal stiffeners. It is divided into three main sections:
(1) The nose section (station 40 to 310), the center section (station 310 to 1490), and the tail section (station 1490 to 1795).
(2) Where plating of .071 inch thickness or less is attached to the fr-, titanium rip stoppers are used for reinforcement and beaded doublers are used in the window belt area forward of the front spar. The frams are generally located at 204nch intervals throughout and longitudinal fuselage splices are reinforced with beaded inner dou'blers and pi-section longerons.
(3) A keel is used to carry structural loads in the main gear wheel-well area and extends from station 680 to lOgO with a splice at station 920. The fuselage is fully pressurized above the floor from station 109 to the aft pressure bulkhead at station 1490, and below the floor in the cargo and accessories compartments,
(4) The cargo compwtments are CUSS D compart=nts, and by design, will not support cotiustion which eUminates the need of having fire extinguishing equip& in the cargo mqartments;
they are also heated to prevent freezing.
c. The pylons are multiple spar and bulkhead structures of high strength aluminum allay, steel, and titanium. The engine mounts are connected to the pylon bulkheads and loads are transferred to the wing through fittings, angles, and clips.
d . The stabilizers, vertical and horizontal, are fill cantilever portions of the empnnage section. The vertical stabilizer is a fixed portion of the fuselage with a removable leading edge and tip l The horizontal stabilizer is a removable three-section unit consisting of a center section and two outboard sections with operating bulkheads between the center and outboard sections.
The leading edge and tips of the outboard sections are removable.
The vertical and horizontal stabilizers contain fittings for rudder and elevator attachment, Chap1 -5 page 3
AC 20-78 11 July 72 6 0 7 0 8 0 GENERAL VISUAL INSPECTTON TIPS. The prim 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.
Vernal indications of failure, such as distorted skin, tilted or sheared 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 emning the exterior surface. For example:
a.
b 0 Buckled skin between rivets at the end of a stiffener or stringer could man 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.
Deep diagonal skin buckles> located over a fray 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.
NONDESTRUCTIVE TESTING (NDT), Nondestructive testing is a maintenance inspection procedure which includes utilization of such maintenance tools as X-ray, ultrasonic, magnetic particles, eddy current, dye penetrant, and others.
a.
b a Maintenance Inspection. NDT permits maintenance inspections without removing components fram'aircraft or tearing down complex assemblies. Defects in various aircraft systems which would esscape detection through normal visual inspection can be identified byNEP.
Training Required. Special NDT training is desirable to make s'ure that the operator is capable of operating the equip& 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 with attendant health hazard of X-ray equipment.
AIRCRAFTWCGEONDIAGW. The wing, fuselage, and empennage station diagrams included in this docent were developed for the DC-~ aircraft and are used as a general reference only. Several models of these aircraft were manufactured and have different station locator nuxribers based on the particular configuration. Since the defective areas generally apply to all models of aircraft, the referenced area can be compared with a similar area and locator on the appropriate station diagram for the particular model of aircraft;.
AC 20-78 9 0 DIiKtNEIONS. _
a.
b 0 C.
d 0 Fatigue. The progressive fracture of a mtalby mans of a fault which develops and spreads under repeated cycles of stress.
stress. The force per unit area of a body that tends to produce FZE&mation.
Stress raiser. A scratch, groove, rivet hole, forging defect, or other structural discontinuity giving rise to a focal point for a local concentration of stress, Corrosion. Gradual destruction of a material by chemical action.
Often evidenced by oxide buildup on the surface. (See Chapter 9) 10 l ABBREVIATIONS USE@ IN THIS Dm.
AOL AD F/S All operators letter Airworthiness Directive Fuselage station Main landing gear Nose landing &ear Partl&miber Service Bulletin Wing station Inboard mtboard Right Wing Ieft Wing Chap1 Par 9 Pa*S(=d6)