0014073 AC NO: AC 20-64 DATE: 8/1/69
EDERAL AVIATION ADVISORY * MINISTRATIO CIRCULAR
DEPARTMENT OF TRANSPORTATION
FEDERAL AVIATION ADMINISTRATION SUBJECT: MAINTENANCE INSPECTION NOTES FOR LOCKHEED L-188
SERIES AIRCRAFT
1. PURPOSE. This handbook describes maintenance inspection notes which can be used for the maintenance support of certain structural parts of Lockheed L-188 series aircraft. This is one of a series of Advisory Circulars to be published on existing aircraft to assist maintenance personnel in directing their attention to those areas which, in addition to normal maintenance practices, have been shown to require special attention.
2. DESCRIPTION. Maintenance on the wing, fuselage, empennage, flight controls, and landing gear 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, IAD-484.3 Washington, D. C. 20590
b. Identify this publication as: Advisory Circular 20-64 Maintenance Inspection Notes for Lockheed L-188 Series Aircraft.
adung Flight Standards Service Director, Initiated by: AC-230/FS-320
AC 20-64 8/1/69
TABLE OF CONTENTS Page No.
CHAPTER 1. MAINTENANCE INSPECTION NOTES. 1
1. Introduction.
2. Description.
3- Background.
4. General Information.
Type of Construction.
General Visual Inspection Tips.
Nondestructive Testing (NDI).
8. Aircraft Station Diagrams.
9. Definitions.
10. Abbreviations Used In This Document. 4 CHAPTER 2. WING. 5
11. I-188 Aircraft Maintenance Information. 5 CHAPTER 3. FUSELAGE. 9
12. I-188 Aircraft Maintenance Informatim. 9 CHAPTER 4. FLIGHT CONTROLS. 11
13. L-188 Aircraft Maintenance Information. 11 CHAPTER 5. LANDING GEAR.
14. I-188 Aircraft Maintenance Information. 13 CHAPTER 6. CORROSION PRONE AREAS. 15
15. General.
16. Exhaust Trail Areas.
17. Engine Frontal Areas and Cooling Air Vents.
18. Battery Areas and Vents.
19. Lavatories, Galleys, and Cabin Floors.
20. Wheel Wells and Landing Gears.
21. Control Surface Recesses.
22. Spot-Welded Skins.
23. Hinges
24. Lap Joints Between Aluminum Alloy Extruded Sections. 16
25. Fluid Entrapment Areas. 17
26. Electronic Package Compartments. 17
27. Control Cables. 17
28. Microbiological Fuel Contamination and Corrosion. 18
AC 20-64 CHG 1 10/26/73 Page No.
CHAPTER 1. MAINTENANCE INFORMATION. 19
29. L-188 Aircraft Maintenance Information. 19 APPENDIX 1. STATION CHARTS. (1 page) Figure A-l. Basic Dimensions.
APPENDIX 2. WING STATION CHARTS. (3 pages) Figure B-l. Wing Station Diagram.
Figure B-2. Wing Skin Planks and Material Index.
Figure B-3. Wing Access and Inspection Provision.
APPENDIX 3. NACELLE STATION CHARTS. (1 page) Figure C-1. Nacelle Station Diagram. 1 APPENDIX 4. FUSELAGE STATION CHARTS. (4 pages) Figure D-l. Fuselage Stations Diagram (Serial Nos. 1001 and Up). 1 Figure D-2. Fuselage Stations Diagram (Serial Nos. 2001 and Up).
Figure D-3. Fuselage Contour Coordinates.
Figure D-4. Fuselage Canted Section. 4 APPENDIX 5. STABILIZER STATION CHARTS. (3 pages) Figure E-l. Stabilizers Stations Diagram.
Figure E-2. Horizontal Stabilizer Stringer Identification.
Figure E-3. Horizontal Stabilizer Stringer Identification. 3 * APPENDIX 6. MAINTENANCE NOTES FOR WING STRUCTURAL AREAS. (57 pages) 1 Figure F-1. Wing Section Upper Surface.
Figure F-2. Wing Section Lower Surface.
Figure F-3. Service Problem Areas.
Figure F-4. Wing Upper Surface• 29 Figure F-5. Wing Upper Surface.
Figure F-6. Wing Lower Surface.
Figure F-7. Wing Lower Surface. 32 Figure F-8. Wing External Structure. 33 Figure F-9. Wing Internal Structure.
Figure F-10. Wing Lower Surface.
Figure F-ll. Wing Upper Surface. 36 Figure F-12. Wing Upper Surface. 37 Figure F-13. Wing Upper Surface. 38 Figure F-14. Wing Upper Surface. 39 Figure F-15. Wing Upper Surface. 40 Figure F-16. Wing Upper Surface. 41 Figure F-17. Wing Upper & Lower Surface. 42
AC 20-64 CHG 1 10/26/73 Page No.
Figure F-18. Wing Upper and Lower Surface. 43 Figure F-19. Wing Lower Surface. 44 Figure F-20. Wing Lower Surface. 45 Figure F-21. Wing Internal Structure. 46 Figure F-22. Wing Lower Surface. 47 Figure F-23. Wing Lower Surface. 48 Figure F-24. Wing Internal Structure. 49 Figure F-25. Wing External Structure. 50 Figure F-26. Wing External Structure. 51 Figure F-27. Wing Internal Structure. 52 Figure F-28. Wing Upper Surface. 53 Figure F-29. Wing Lower Surface. 54 Figure F-30. Wing Lower Surface. 55 Figure F-21. Wing Upper Surface. 56 Figure F-32. Wing Upper & Lower Surface. 57
AC 20-64 Page 1 8/1/69 CHAPTER 1. MAINTENANCE INSPECTION NOTES
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 the Lockheed I-188 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 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. DESCRIPITON• The circular contains guidance material for performing inspection and maintenance on wing, fuselage, empennage, flight controls, and landing gear structures. 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 diagrammatic sketches and station identifications of the wing, fuselage, and flight controls. In addition, there is a listing of selected maintenance difficulties which have been reported during 1967 and 1968.
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 and airworthy 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 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 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 Lockheed I-108 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 damage. Operators are urged to become conversant with the manufacturer's recommendations and make certain that responsible maintenance personnel are knowledgeable on this subject.
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Page 2 AC 20-64 8/1/69
b. 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, the fuselage group, and tail group. The primary structure, shown in detail in this manual, consists of the fuselage, nacelles and the box beam sections of the 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 element will not result in the loss of the complete structural component.
a. The wing is an all-metal, full cantilever-type structure and consists of a center section, an outer section, flaps, fillets and ailerons.
The primary structure of the wing incorporates two main beams, upper and lower extruded surface panels, and ribs to stabilize the structure and maintain surface contour. Wing flaps are actuated by ball-bearing screw jacks and travel on steel tracks. The internal structure and skins are fabricated of aluminum alloy. Ailerons and trim tabs are of conventional design and constructed of aluminum alloy. Leading edges are attached to the front beam by hinges and incorporate provisions for ice elimination. Trailing edges are fabricated by the use of the metal-bond process, an outside skin bonded to an inner beaded skin. A major portion of the lower trailing edge is sectioned into hinged doors for inspection and maintenance.
b. The fuselage is of conventional semimonocoque construction, using skin, stringer, and circumferential-irame combinations. The skin Large doublers, made of the same materials and usually chem-milled'¿p panels, for the most part, are made of 2024-T3 or -T4 material. are used around doors, windows, and, generally, around all cutouts the skin. The frames from station 200 to 1110 are mainly 19 inches apart with reinforced structure in the propeller and door areas.
Stringers are made, for the most part, oi formed sheet-metal sections, except near openings where heavier extruded sections are used. The floor support structure consists mainly of extruded vertical and transverse members attached to the fuselage frames. In the center section (over the wings) and in the nose section, longitudinal beams support the floor. Floor panels are of plywood in the aisles and vestibules, and metal-honeycomb-sandwich elsewhere. The latter contains electric-heating elements in passenger seating areas.
The entire fuselage is pressurized between the forward pressure bulkhead (forward of and below the flight station) and the rear pressure bulkhead (rear of the lounge or aft lavatory). The main manufacturing joints are at stations 200 and 1117. Along the main passenger compartment from station 219 to approximately 968, the fuselage is a constant section.
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AC 20-64 Page 3 8/1/69 The stabilizers consist of the horizontal stabilizer and tips, elevator and tabs, vertical stabilizer and tip, rudder and tab, fillets, and dorsal. Each member has an all-metal aluminum frame covered with aluminum skin. The horizontal stabilizer 1s attached to the fuselage tail section by four continuous beam caps and four continuous stringers. The vertical stabilizer is attached to the fuselage tail section by the extension of four beam caps and four stringers. The dorsal is connected to the fuselage by means of an attaching angle. There is a shear pin that connects the top of the dorsal to the vertical stabiiizer at fuselage station 1117.
6. GENERAL VISUAL INSPECHION TIPS. The primary structure of the aircraft 18 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 obvious. Wrinkled skin, shelous. Veiled in, ole, and tited vets, 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:
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). Simply stated, nondestructive testing 18 preventive maintenance. This includes utilization of such maintenance tools as X-ray, ultrasonic, magnetic particles, eddy current, dye penetrant, and others.
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.
b. Training Required. Special NDI training 1s desireable 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 Chap 1 Par 5
Page 4 AC 20-64 8/1/69 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 I-188 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. (See Appendices 1 through 5.)
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.
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.
d. Corrosion. Gradual destruction of a material by chemical action.
Often evidenced by oxide buildup on the surface.
10. ABBREVIATIONS USED IN THIS DOCUMENT.
AD Airworthiness Directive F'BC Fixed base check FCD Fleet campaign directive FS Fuselage station HSS Horizontal stabilizer station LAC Lockheed aircraft MBC Main base check MLG Main landing gear NIG Nose landing gear P/N Part number SB Service Bulletin SIL Service Information Letter Total time TAT Total aircraft time TSN Time since new TSO Time since overhaul T ST Total ship time VSS Vertical stabilizer station WS Wing station Par 7 Chap 1
AC 20-64 Page 5 8/1/69 CHAPTER 2. WING
11. L-188 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, wing structural references apply to both left and right wings.
Lockheed Reference
a. Lower Wing Skin Planks. For Details
(1) Lower wing skin plank damage was caused SIL-61 by integral engine start system compressor 10/17/62 line rubbing in #2 and #3 nacelles.
(2) Cracks occurred in the lower #3 wing skin SB 601 plank forward of the MG fulcrum fitting. 6/24/63 (Over 900 hours TSN.)
(3) SB 587 alert wire was issued to inspect #4 SB 587A lower wing plank drain hole for cracks at 4/10/64 station 159. Plus AD 65-15-4
(4) Cracks have been found at the fastener holes SB 631 around the fuel sight gage and fuel overflow 9/6/65 openings on the left- and right-hand lower wing planks. The cracks occur at wing station
128.0 and in the wing reinforcing doubler at station 266.0.
(5) Cracks have been found in lower wing plank #1 SB 653 between WS 205 and WS 275. 7/3/68
b. Upper Wing Skin Planks.
(1) Cracks have been found which appear to be SB 565 static fractures originating on the #l 4/27/62 upper wing plank inner surface.
(2) Cracks have been found in the upper surface SB 619A in the area of the main landing gear rib 5/21/65 forgings. These areas were previously rein- Plus AD forced by doublers in accordance with SB 65-9-4 306 and 337 except aircraft, LAC serial #1145 thru 1148 and 2020-2022, which were delivered with internal reinforcements.
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Page 6 AC 20-64 8/1/69
(3) Cracks have been found at screw holes 1n the SB 632 wing upper plank #2, at the plank #1 and #2 6/29/65 splice between WS 212.0 and 230.0.
Cracks have been found in the trailing edge of SB 634A wing planks #6, #7, and #8 at wing station 143 10/8/65 LEFT and RIGHT upper surface. In two cases, the backup fitting, P/N 803900, for the flap track attachment was also cracked.
(5) This reference applies to the inspection of SB 6250 wing plank splices aft of the main landing 5/16/66 gear fulcrum fitting and provides additional Plus AD repair 1nstructions for the WS 209 area (see 66-11-2 d(2) page 7).
This revision provides instructions to reduce SB 600A the possibility of cracks developing in the 2/21/68 upper wing planks under the nacelle skate Plus AD The original bulletin pertained only 64-11-3 to the inboard nacelle skate angles, but this revision supplies reinforcement for ALL
(7) A considerable number of cracks have been found SB 649 in the #l upper wing plank at the nacelle 2/29/68 fillet attachments. Cracks have been found at SB 665 the inboard side of all four nacelles at the Plus AD's attachment of the nacelle fillet with the 68-11-2 upper #1 plank. 68-23-5
(8) Cracks have been found in the #3 upper wing SB 652 plank along the first row of fasteners 4/30/68 adjacent to the skate angle of the outboard nacelle at WS 346.0.
c. Outer Wing to Center Wing Attach Fittings.
This SB revisionwas issued to identify SB 633A/633B requirements for the outer wing front cap fittings, 9/3/65 8 P/N 807352 and P/N 807354; specifically, corrosion 9/24/65 of fittings, attachment bolts, and boltholes. Plus AD 66-5-3
d. Wing - MG Ribs. These service bulletins instruct operators as follows:
(1) To inspect the MG ribs in each wing for SB 630 fatigue cracks in the web fillets at the 7/20/65 junctures of the rib truss members with the rib upper chord member. Similar cracks Par 11 Chap 2
AC 20-64 Page 7 (and 8) 8/1/69 have also been found in the web fillet between the forward truss member and the upper chord member beneath the #? wing plank.
(2) To inspect the vertical legs of the upper and SB 639 lower caps of the wing ribs for cracks at 11/7/66 wing stations 167 and 209.
Wing-to-Nacelle Attachment Plate. Cracks have been SB 638 found in the wings-to-nacelle attachment plate, 10/17/66 P/N 810054-1, which is located inside the inboard nacelle on the lower front beam of the LEFT WS 209.
(Propeller torque loads on the #2 nacelle augment the normal stresses on this plate.)
f. Wing Rear Beam Clips. Cracks have been found in P/N SB 654 805483-1 (WS 179), and P/N 805491-1 (WS 197) rib 4/8/68 attach clips location (dry bay area), at the rear beam forward face upper attachment. Cracks occur in the 0.16 radius of the flange relief cutout and extend toward the nearest fastener hole.
& - Wing Upper and Lower Access Door Lands. Corrosion SB 606 found on the lower wing plank access door lands 11/18/63 appears to be caused by condensation. (Door lands are the area surrounding the access opening in the wing plank.)
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AC 20-64 Page 9 8/1/69 CHAPTER 3. FUSELAGE
12. I-188 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, fuselage structural references apply to both left and right sides.
Lockheed Reference
a. Fuselage Stringers Station #1117. This For Details service bulletin provides for inspection SB 574 of the underfloor stringers at the aft 10/3/62 pressure bulkhead for cracks. The Revised 12/26/62 bulletin was later revised to cover all underfloor stringers, 1 thru 72.
b. Flight Station Pressure Deck. Cracks have SB 609A been found in the flight station pressure 11/2/63 deck structure, butt line 40 right beam, Revised 3/30/65 lower beam cap flange. Cracks in this location could result in a loss of cabin pressure.
Reported cracks have occurred on aircraft with over 13,000 total flight hours.
Forward and Aft Cargo Door Frame Corners. SB 608A Cracks have been found in the lower forward 2/5/65 and aft cargo door frames. Revised SB 608B 2/18/65
d. Fuselage Main Frame Fittings. A considerable SB 644 number of cracked main frame fittings have 2/10/67 been found at FS 570 and FS 695 Revised SB 644A 12/5/67 Plus AD " 67-11-4 Fuselage Bulkhead Ring Intersection with Center SB 646 Wing. Cracks have been found at the intersection 4/12/68 between the wing center section lower surface and the fuselage rings at fuselage stations 571 and 694.
f. Cabin Window Support Structure. Cracks have SB 647 been found in fuselage station 853.5, (cabin 5/6/68 window support structure.)
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