11 July 72 AC 20-78 incorporated in the structure for attachment 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 disassembled except for major repair of primary structure.
The fuselage 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:
The nose section (station 40 to 310), the center section (station 310 to 1490), and the tail section (station 1490 to 1795).
Where plating of .071 inch thickness or less is attached ment and beaded doublers are used in the window belt area forward of the front spar. The frames are generally located at 20-inch intervals throughout and longitudinal fuselage splices are reinforced with beaded inner doublers 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 1090 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.
The cargo compartments are Class D compartments, and by design, will not support combustion which eliminates the need of having fire extinguishing equipment in the cargo compartments;
they are also heated to prevent freezing.
The gylons are multiple spar and bulkhead structures of high strength aluminum alloy, 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 full cantilever portions of the empennage section. The vertical stabilizer is a fixed portion of the fuselage with a removable leading edge and tip. 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.
Chap 1 Par 5 Page 3
AC 20-78 11 July 72 GENERAL 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.
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:
a. 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.
b. 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.
7• NONDESTRUCTIVE TESTING (NDI). 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. 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 can be identified by NDI.
Training Required. Special NDT training is desirable 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 with attendant health hazard of X-ray equipment.
8. AIRCRAFT STATION DIAGRAMS. The wing, fuselage, and empennage station diagrams included in this document were developed for the DC-8 aircraft and are used as a general reference only. Several models of these aircraft were manufactured and have different station locator numbers 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.
Chap 1 Page 4 Par 5
11 July 72 AC 20-78 9• DEFINITIONS.
Fatigue. The progressive fracture of a metal by means of a fault which develops and spreads under repeated cycles of stress.
b. Stress. The force per unit area of a body that tends to produce a deformation.
c. Stress raiser. A scratch, groove, rivet hole, forging defect, or other structural discontinuity giving rise to & focal point for a local concentration of stress.
d. Corrosion. Gradual destruction of a material by chemical action.
Often evidenced by oxide buildup on the surface. (See Chapter 9)
10. ABBREVIATIONS USED IN THIS DOCUMENT.
AOL All operators letter AD Airworthiness Directive F/S Fuselage station MIG Main landing gear NIG Nose landing gear P/N Part Number SB Service Bulletin W/S Wing station I/B Inboard 0/B outboard R/W Right wing I/W Left Wing Chap 1 Page 5 (and 6) Par 9
11 July 72 AC 20-78 CHAPTER 2. WING
11. DC-8 AIRCRAFT MAINTENANCE INFORMATION. The following is a listing oi significant maintenance difficulties that have been reported by air carriers. This information may be useful in identifying structural inspection areas. ixcept where noted, wing structural references apply to both left and right wings.
a. McDonnell Douglas Center Wing Section Reference For Details The vertical flange of the inner SB 57-9 wing bulkhead lower chord member 6/28/60 found tracky. Inspotion bhould at station X also include upper chord member.
(2) The forward tang of the lower SB 57-37 front spar cap has been found 1/29/65 cracked at W/S Xew 46.000.
(3) Cracks have been found in the web SB 57-58 of the wing trailing edge panel 1/19/68 between stations Xw 5.812 and XwI 60.000.
Corrosion has been found on the SB 57-31 inner surface of integral fuel 8/23/63 tank access doors and doubler Reissued lands on aircraft with approxi- 11/1/64 mately 9000 hours flying time.
The corrosion was found on the topside doors and lands.
b. Inboard Wing Section.
(1) Leading edge formers have been SB 57-11 Pound cracked at the upper and 5/19/60 lower segments of the aft end. The cracks were between 1/4" to 2 3/4" in length. Inspection of these formers should be from station Xes
138.750 through Xes 245.000.
Cracks have been found in the bulk- SB A57-7 head upper and lower caps at station Reissued Ars 139.000 just forward of the rear 9/24/64 SB 57-7 Rev 1 7/25/60 and AD 60-8-3 Chap 2 Far 11 Page 7
AC 20-78 11 July 72
(3) An alert bulletin was issued due to cracks SB AST-17 being found in the lower wing flap support Reissue No. 2 fitting chord member in the bulkhead at 3/20/61 station Ars 358.000. The cracks occurred in the bulkhead chord member between the barrel nut retainer hole and the end of the part.
Cracks have been found in the lower lead- SB 57-19 ing edge skin of the pylon stub wing Revision No. 2 adjacent to the I/B side of each 1/B pylon. 1/26/67 The cracks emanate from the inside radius of the skin cutout at the intersection of the edge of the skin and the pylon. This also applies to the outboard wing section leading edge skin inboard of the 0/B pylons.
Several operators have found cracks in the SB 57-30 lower front spar cap tang at W/S Xis 67.531. Rev 2 The cracks occurred on the forward tang of 10/31/67 and the spar cap at the splice. Cracks have SB 57-34 also been found in the upper front spar cap Rev 2 tang at the splice at W/S Xps 67.531. 10/27/67 Loose attachments in the top trailing edge SB 57-41 skin have been reported by operators on 9/7/66 aircraft with more than 10,000 flight hours.
The manufacturer modified all applicable models prior to delivery of fuselage #285 and sub sequent. The modification installs a doubler from W/S Xw 70.000 to Xw 113.000.
A service bulletin was issued to inspect for SB 57-46 cracks in the I/B aft corner of the leading 3/6/67 edge upper slot door assemblies. This bulletin applies to aircraft prior to fuselage #315.
c. Outboard Wing Section.
(1) An inspection and rework bulletin was issued SB A57-15 as a result of a report of an aileron hinge Reissue #l fitting lug breaking off at station Xa 448. 8/8/60 Electrical junction box support clips on the SB 57-16 rear spar have been found cracked between 11/29/60 station Yrs 470 and Xrs 479. The cracks occurred in the clip lobe's at the rear spar attach point.
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AC 20- 78 11 July 72
(3) Operators have reported cracks in the SB 57-25 stub wing leading edge of the 0/B Rev 2 pylons in the area of the pneumatic 8/27/62 duct cutout.
(4) Cracks have been found in the wing SB 57-48 leading edge lower structure between 3/3/67 the opening for access door 520J and percent wing leading edge. 526.760 on aircraft with four Cracks have been found in the wing SB 57-59 leading edge lower surface skin on 4/11/68 aircraft with 15,000 to 20,000 flight hours. The cracks developed between access door 520J and W/S X 454.000 on aircraft with standard wing leading Par 11 Chap 2 Page 9 (and 10)
11 July 72 AC 20-78 CHAPTER 3. FUSELAGE
12. DC-8 AIRCRAFT MAINTENANCE INFORMATION. The following 1s & listing of significant maintenance difficulties that have been reported by air carriers. This information may be useful in identifying structural inspection areas. Except where noted, fuselage structural references apply to left and right sides of the fuselage.
Tail cone structure has been found cracked. SB 53-17 The cracks are a result of sonic vibration 10/5/60 which is prevalent in the tail cone area SB 53-11 during operation of the aircraft. Rev 2 5/1/61 SB 53-13 Rev 2 3/24/61 SB 53-19 11/1/60 SB 53-25 Rev 1 2/27/62
b. Cracks have been reported in the aft vertical SB 53-21 stiffeners of the 0/B MG wheel well webs. 3/24/61
c. Cracked fuselage to skin shear clips have been found cracked on aircraft with 5,000 hours Rev 2 SB 53-28 flight time. The affected areas are at F/S 6/26/53 Y 640.000 between longerons 22 and 23 and F/S Y 660.000 between the cusp line and longeron 23.
d. Cracks have been found in longeron 24 at F/S SB 53-32
980.000 on aircraft with 10,000 or more Rev l flight hours. 9/17/65
e. Cracks in the MG I/B door actuating cylinder support fittings have been reported. SB 53-33 1/21/66 fittings are located on the left and right sides of the keel beam at F/S 920.000.
Cracks in the domed aft pressure bulkhead have been reported. Cracks were a result of SB 53-41 10/17/67 fatigue and occurred at approximately 15,000 flight hours.
Cracked vertical angles located at the upper SB 53-46 portion of the aft flat pressure bulkhead 3/28/68 have been reported by one operator on an aircraft with 14,000 flight hours.
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AC 20-78 11 July 72
h. Fuselage skin corrosion has been found on SB 53-53 an aircraft with approximately 25,000 12/20/68 flight hours. The corrosion was in the scuff plate area of passenger, service, and cargo doors.
Fuselage frame fittings have been found AOL 8-169A corroded on aircraft with between 21,000 8/30/68 and 30,000 flight hours. The corroded fittings were located at F/S 920 and 960.
Chap Page 12 Par 1
11 July 72 AC 20-78 CHAPTER 4. FLIGHT CONTROLS
13. DC-8 AIRCRAFT MAINTENANCE INFORMATION. The following is a listing of significant maintenance difficulties that have been reported by air carriers. This information may be useful in identifying structural inspection areas. Except where noted, ilight control structural references apply to left and right sides.
a. Flap support fittings on the aft side of SB A27-5 the rear spar have been found cracked. Reissue #2 Examination indicated stress corrosion 3/1/61 developed and cracks propagated from the corroded area.
b. Operators have experienced cracking of the SB 27-48 rudder nose rib webs at the three hinge point locations and in the rib to spar attach angles, (Stations Zy 105.000, Zy 162.906, and Zr 220.813).
c. An alert bulletin was issued by the manufacturer SB A27-66 due to a report of a left 0/B elevator geared 6/20/60 tab push rod being broken at the aft rod end fitting, rod P/N 4702890.
d. The aileron reversion mechanism forward gripper SB 27-95 has been found cracked at the lower clevis ends Reissue #l which attach to the end of the aileron tab 5/18/62 lockout cylinder piston end fitting.
e. Clevis P/N 2619862 on the rudder lockout SB A27-100 cylinder was found broken. This allowed Reissue #2 the rudder to revert to manual with hydraulic 9/24/64 and power still on causing the rudder to lock AD 61-6-4 in its last position.
f. Cracks have been found in the aileron tab SB 27-115 lockout mechanism support brackets Rev #1 10/25/01 P/N 4643350. and AD 62-2-4
g. Wing flap actuating cylinder barrels have SB 27-118 been found cracked. Examination of failed Reissue #2 cylinders disclosed corrosion in the internal 12/4/61 portion of the barrel.
Wing flap support track assemblies have been SB 27-123 found cracked at W/S Xp 219.498. Analysis 12/27/61 indicated the cracks could have been caused by stress corrosion.
Chap 4 Par 13 Page 13
AC 20-78 11 July 72 Wing flap rod end bearings have been found SB 27-127 cracked with more than 5000 hours. Rev. #2 The cracked bearings were located at W/S 1/28/64 and 98 and 219 in the area of the bearing case AD 62-12-4 adjacent to the bearing dust shield.
j• Wing flap actuating cylinder barrels have SB 27-134 failed. Both mid-wing and 0/B actuating Reissue #1 cylinders have been found cracked. 10/19/62 SB A27-134 Reissue #2 10/13/64 and ADS 62-16-2 and 62-24-4 Wing flap link assemblies P/N 5644642-501 SB 27-137 at W/S X 97.906 and P/N 5644644-501 at Rev. #1 W/S Xp 219.498 have been found broken on 1/8/64 several occasions.
1. Cracks have been found along the horizontal SB 27-142 centerline of the forward attach lugs of the flap Reissue #l link support assemblies on aircraft with 5/15/63 more than 8000 hours,
m. Operators have experienced failure of the SB 27-159 0/B wing slot assembly, P/N 3770143-1, on Reissue #1 aircraft with four percent extended wing 2/23/65 leading edge.
n. Cracked flap hinge support fittings have been SB 27-217 found in the 0/B flap center hinge base Rev. #1 assembly on aircraft with between 8000 and 10/9/68 11,000 hours..
o. Rudder link, P/N 2619201, failures have SB 27-218 occurred on aircraft with 23,000 to 26,000 Rev. #1 hours. 10/18/68 Cracked aileron tab rod end assemblies have SB 27-223 been found on aircraft with 3,000 to 29,000 12/6/68 hours.
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