CONSOLIDAmD REPRINT-FEBRUARY 1977 (includes Changes 1 and 2) AC !6: 20-83 DATE: 17 Jan 73
ADVISORY
CIRCULAR MAINTENANCE INSPECTION NOTES FOR BOEING B-737 SERIES AIRCRAFT
DEPARTMENT OF TRANSPORTATION
FEDERAL AVIATION ADMINISTRATION Initiated by: AFS-230
At NO: 20- 83 DATE: 1Z Jan 73
ADVISORY
CIRCULAR
DEPARTMENT OF TRANSPORTATION FEDERAL AVIATION ADhlINISTRATION SUBIE@T: MAINTENANCE INSPECTION NOTES FOR BOEING B-737 SERIES AIRCRAFT
1. PURPOSE. This advisory circular provides maintenance inspection notes which can be used for the maintenance support program for certain structural parts of the B-737 series aircraft.
2. DESCRIPTION. Maintenance inspection matters on the wing and fuselage are reviewed with a view toward supplementing information currently available.
3. REFERENCES.
a.
b.
C.
d.
e.
4. HOW Advisory Circular 20-61, Nondestructive Testing Techniques for Aircraft.
Advisory Circular 65-9, Airframe and Powerplant Mechanics General Handbook.
Advisory Circular 43.13-1, Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair.
Defense Metals Information Center ('DMIC) Report, S-25, dated 1 June 1968, Current Problems and Prevention of Fatigue.
Advisory Circular 20-9, Personal Aircraft Inspection Handbook.
TO GET THIS PUBLICATION.
a. Order additional copies of this publication from:
Department of Transportation Distribution Unit, TAD 484.3 Washington, D. C. 20590 Initiated by: ~~~-230
AC 20-83 17 Jan 73
b. Identify this publication as: Advisory Circular No. 20-83, ' Maintenance Inspection Notes for Boeing B-737 Series Aircraft.
&&?qqj- C. R. MELUGIN, JR.
Acting Director, Flight Standards Service Page ii
l/31/75 AC 20-83 CHG 2
TABLE OF CONTENTS Page No.
1. Introduction. 1
2. Description. 1
3. Background. 1
4. General Discussion of Structure Surveillance. 1
5. Type of Construction. 3
6. Aircraft Station Diagrams. 4
7. Abbreviations Used In This Document. 4
8. Maintenance Reports. 4 APPENDIX 1. CORROSION (2 pages) 1 APPENDIX 2. STATION CHARTS (6 pages) Figure 1. Principal Dimensions 1 Figure 2. Body Station Diagram 2 Figure 3. Wing Station Diagram 3 Figure 4. Engine and Nacelle Station Diagrams 4 Figure 5. Horizontal Stabilizer and Elevator Station Diagrams 5 Figure 6. Vertical Stabilizer and Rudder Station Diagrams , 6 APPENDIX 3. NONDESTRUCTIVE TESTING (5 pages) 1 Page iii
B/8/74 AC 20-83 CHG 1
3.
2.
3.
*
4.
INTRODUCTION. This-advisory circular provides maintenance information which can be used, but is not required to be used, by mechanics, repair agencies, owners, and operators in developing maintenance programs, making improvements in existing programs, and conducting inspection and repairs on certain structural parts of Boeing B-737 airplanes. The material is based, in part, upon infocFtion 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 30 that it is not lost.
DESCRIPTION. This circlzlar 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 is a listing of selected maintenance difficulties which have been reportecl since 1968 by air carrier operators.
BACKGROUND.
a.
b.
Used Aircraft. The Administrator realizes that several different types of transport aircraft are being phased out of service by some airlines and are being purchased by other operators who may not be familiar with the scope of required maintenance atid the means which have been used to keep the aircraft in a safe condition. * Maintenance "Know How." Since maintenance %now howtr 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.
GENERAL DISCUSSION OF STRUCTURE SURVEILLANCE.
a. Manufacturer's Service Bulletins. The manufacturer has published service bulletins containing its recommendations concerning the inspection, repair, and modification of aircraft. Most of these bulletins cover known areas; however, some are predictive in nature and have been issued even though no fatigue damage has been identified in the fleet. Because of differences in structural configuration, most service bulletins apply only to certain aircraft. Effectivity is shown in each bulletin. Additional bulletins may be published by the manufacturer, and a service bulletiqindex is available from the manufacturer which is updated periodically.
b. Other Documentation. Further, the manufacturer has published the following documents to aid in maintaining the aircraft in serviceable condition:
* Maintenance Planning Document (D6-17594) Maintenance Manual; @6-series different for each operator) Overhaul Manual, (D6-17370) Structural Repair Manual, (D6-15565).
NIYIY Document (D6-7170) * The above documents are updated from time to time by the manufacturer.
Structural Item Interim Advisories are published by the manufacturer to notify operators of newly found problems which may be of fleetwide significance and may or may not be followed by service bulletins.
c. Maintenance Action. For adequate maintenance of the B-737 ai-z-plane structure, every operator sho,uld have in his possession and be conversant with the above documentation, including service bulletins applicable to his particular aircraft. He should also obtain complete service records from previous owners and become familiar with the struct&al history of his aircraf't, including information on maintenance procedures followed, major repairs made, and preventive modifications and/or repair work incorporated per service bulletins. This is essential to carry out the follow-up procedures required, and to avoid unnecessary work where corrective action has already been taken.
(1) The new operator should contact the manufacturer regarding any areas requiring clarification.
(2) The operator should keep himself informed of new developments and arrange to be supplied with revised and new documentation by the manufacturer. Consultation with the manufacturer and/or more experienced operators should take place from time to time as necessary, to establish which service bulletins have structural significance and when they would best be incorporated.
(3) The maintenance program established by the new operator should reflect changes in environment and Gage of the aircraft (e.g., shorter flights, intermittent use, etc.).
d. Airworthiness Directives. The material in this circular does not supersede requirements of airworthiness directives (AD's) issued by the FAA. Although manufacturers'service bulletins may be referred to in AD's, the bulletins do not supersede any requirements of the AD’S.
e. Certification. Type certificate data sheet No. A16m was issued 15 December 1967 for model 737-100 and 21 December 1967 for.model 737-200 to the Boeing Company, Renton, Wa. The basis for certification was FAR 25, amendments 25-1 through 25-3, 25-7, 25-15; FAR 21;
Page 2 Par 4
17 Jan 73 AC 20-83
5.
PAR 1; and special conditions. (See type certificate data sheet A16WE for information relating to special conditions.) The latest revision of type certificate data sheet Al&Q, at the time this document was published, was revision No. 5 dated 1 April 1972.
TYPE OF CONSTRUCTION. The aircraft structure can be classified into three major components; the fuselage, the wing, and the empennage.
These components have been designed to provide maximum strength with minimum weight by providing multiple load paths so that the failure of any one structural element will not result in the failure of the complete structural component. The materials most corrmonly used throughout the structure are aluminum,' steel, and magnesium alloys. In secondary structural areas and many flight control surfaces, aluminum and fiberglas honeycomb core material is extensively used.
a. The fuselage is a semimonocoque structure with the skin reinforced bgircumferential frames and longitudinal stringers. It consists of four section* ,--body sections 41, 43, 46., and 48; with section 41 located between stations 178 and 360, section 43 between stations 360 and 540, section 46 between stations 540 and 1016, and section 48 between stations 1016 and lZ?l7. The entire fuselage shell between stations 178 and 1016 is pressurized except for the nose gear well and the cutout for the center wing box and main landing gear well.
b. The wing is composed of a left wing box, center wing box, and a right wing box. The left and right wing boxes ar e cantilevered from the center wing box and the thickness and chord of each wing taper down toward the tip and sweep badk from the center wing box. The surfaces of the wing boxes consist of upper and lower skin panels and front and rear spars. Throughout the wing boxes, the skin panels are reinforced by spanwise stringers and the spars are reinforced by vertical stiffeners.
(1) The left and right wing boxes are reinforced by chordwise ribs with the greatest portion of their enclosed volume sealed to serve as fuel tanks, The center wing 'box is reinforced by spanwise beams and &ontains bladder-type fuel cells. On each wing, the leading edge structure is cantilevered forward of the front spar. The trailing edge structure and control surfaces are cantilevered aft of the rear spar.
(2) Two flaps and three extendable slats are supported by the wing leading edge on each wing. Along the trailing edge of each wing an I/B and O/B flap, an aileron, and four spoilers are installed. The leading edge of each wing contains a pressure relief panel to alleviate pressures due to leaking or ruptured ducts associated with the engine. The pressure relief panel is designed to open at a pressure of.one psi.
Par 4 Page 3
a.
20-83 CfIG 1 8/8/74
c. The empennage consists of a dorsal fin, a vertical fin, an adjustable horizontal stabilizer, a rudder, and elevators. The left and right horizontal stabilizers are removable from the center section truss located within the fuselage and have removable leading edges. The elevators are aluminum frame structures with leading and trailing edge spars, ribs, and a fiberglas skin. Each elevator contains three balance panels and a control tab. The rudder is a monospar aluminum alloy structure with chordwise ribs and honeycomb core fiberglas skin.
It does not contain a tab. * AIRCRAFI' STATION DIAGRAMS. The wing, fuselage, and empennage station diagrams included in this document were developed for the B-737 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 aircraft.
ABBREYIATIO~S USED IN THIS DOCUMEZT.
O/B 0
R/H TAT TSN TSO Federal Aviation Regulation Inboard Left Hand Main Landing Gear Nose Landing Gear Outboard Part Number Right Hand Total Aircraft Time Time Since New Time Since Overhaul MAINTrnANCE REPORTS. The following is a listing of selected maintenance difficulties experienced, representing examples of reports submitted by air carrier operators. This information may be useful in identifying structural problem areas. It should be noted that this is a partial list only and covers just a portion of time in the history of the B-737 series aircraft.
a. Fuselage.
(1) During routine inspection, on two occasions a two-inch crack was found at the fuselage vertical pressure web above the wing rear spar below the cabin floor, 30" left of the tiabin center line at station 663.75, TAT 4989 hours and 5113 hours. * Page 4 Par 5
818174 * (2)
(3)
(4)
(5)
(6)
(7)
(8) AC 20-83 CHG 1 Routine inspection of the stub beam at the outboard lower chord, P/N 65-47995-2, disclosed a 4" spanwise crack just above the radius, R/H side of fuselage at station 559. TAT 5028 hours.
During routine inspection, on two occasions skin cracks were found originating at the aft rivet hole of the L/H vortex generator at station 1114. TAT 3533 and 3634 hours.
Routine service check disclosed a stringer cracked in two places at station 1115 L/H side. TAT 5462 hours. Associated with item (3) problem.
Flight returned.due to the L/H sliding window outer pane being cracked, P/N 5-71762-25. TSN 4130 hours. The outer pane has no structural significance.
During routine inspection a 3" crack was found in the beam-toframe attach clip, P/N 69-53023-2 in the R/H wheel well at station 663.75. TAT 6394 hours.
An unscheduled landing was made due to a shattered outer pane of the L/H windshield. TAT 5195 hours. The outer pane has no structural significance.
Routine inspection disclosed the lower wing to body attach angles cracked at left and right body station 540. *
b. Wing.
(1) A flight was interrupted due to loss of a 50" x 20" section of upper skin on the L/H I/B spoiler. TSN 1970 hours.
(2) During routine inspection, an 11" x J-3/4" section of the R/H aileron lower skin was found delaminated from the honeycomb core at the leading edge. TSR 2270 hours.
(3) The abnormal appearance of a wing flap in flight resulted in an unscheduled landing. Inspection after landing disclosed a broken 82 flap fairing arm, P/N 65-68269-7.
(4) During flight-crew walkaround check, part of the top skin was found to be missing on the L/H I/B gound spoiler. TAT 5590 hours.
(5) A crew report of high frequency vibration inflight disclosed the cause to be loose top skin at the I/B end of #4 ground spoiler, P/N 65-46452-35. TAT 6221 hours.
Par 8 Page 5
AC 20-83 17 Jan 73
(6) During routine inspection, three cracks were found in the skin of #2 engine nose cowl. The cracks were 2", 4%", and 5" in length. Nose cowl P/N 65-55750. Nose cowl TSN 4181 hours.
(7) During routine inspection, on three occasions, gusset plate P/N 65-45402-60 was found cracked, R/H side rear spar lower wing joint at WBL 70.85~
(8) Scheduled maintenance check found the #5 slat I/B attach fitting broken, P/N 69-40609-2. TAT 5374 hours.
(9) During scheduled inspections, the L/H and R/H I/B trailing edge flap ribs were found cracked at the O/B flanges at WBL 82.58 and WBL 117.10. Rib P/N's 69-40664-3, 65-50757-7, and 65-40663-5.
TAT ranged from 4021 hours to 6948 hours.
(10) During scheduled inspection, the top skin of the R/H aileron was found to be delaminated at a skin joint at the front spar.
Aileron TSN 5774 hours.
(11) Routine service check disclosed the #l and #& leading edge slat torsion tubes were cracked, tube P/N 69-50753-2. TAT 6310 hours.
(12) A 6" crack was found in #l engine nose cowl, cowl TSN 4332 hours.
(13) Aircraft returned after leaving gate due to broken # leading edge flap arm P/N 69-37841-7. TAT 8379 hours.
(14) Crew report that the L/H trailing edge flap would not retract led to detection of a broken cable, P/N EAC!C13AP~-772. TAT 6130 hours.
(15) During scheduled inspection, the #l leading edge slat O/B torsion tube was found broken at the I/B end of the detent arm, tube P/N 65-55514-29. TAT 2888 hours.
(16) A crew report that #5 slat did not fully retract and # was cocked at an angle when flaps were extended disclosed that bracket P/N 69-40609-2 was broken at station 145.83.
(17) Crew reported that aircraft rolled to right when flaps were extended. Inspection found the R/H I/B aft flat cable tensioner terminal fitting and cable broken. TAT 5227 hours.
(18) During routine inspection, a crack was found in the L/H MLC beam O/B stabilizer link fitting, P/N 69-38823-5. TAT 3336 hours.
Page 6 Par 8