5 Dec 72 AC 20-82
23. LAP JOINTS BETWEEN ALUMINUM ALLOY EXTRUDED SECTIONS. Extruded sections of high-strength materials such as 7075 or 7178 aluminum alloys are more susceptible to intergranular corrosion than are other aluminum alloys. Application and maintenance of chemical processes, sealants, paints, or combinations of these protective measures have proven most effective in controlling corrosive attack on these materials.
If intergranular corrosion occurs, it is usually found around fasteners or in lap joints. It is evidenced by raised areas or lumps under the paint film, and there have been instances where the attack has progressed to such an extent that there were actually bulges in the faying surfaces. These raised areas, lumps, and bulges are due to the accumulation of corrosion products, which take up more volume than did the affected material before it corroded.
FLUID ENTRAPMENT AREAS. Design specifications require that aircraft have drains installed in areas where water may collect. However, if drains are rendered ineffective because they are clogged by debris, sealant, etc., or because the level of the aircraft is changed from that of a normal ground attitude, corrosive agents can collect in a localized area. Low-point areas and drains should be inspected frequently to prevent the inception of corrosive attack.
Low points of integral fuel tanks are areas where water condensate can collect. This water condensate is of doubtful purity, and if permitted to stand it can permeate the protective coating of the tank and bring many corrosive agents held in suspension in contact with the vulnerable metallic surfaces. Water condensate should be drained regularly from fuel tanks and the integrity of the tank sealant maintained to prevent corrosion of integral tank surfaces.
hen considering iluid entrapment areas, one inevitably thinks oi airraft drinking water and wash water systems. Corrosion in these systems is rare because they are fabricated from nonmetallic materials and/or stainless steel. Water stagnation should pose no problems so long as sanitation regulations are heeded.
ELECTRONIC PACKAGE COMPARTMENTS. Often the safety of those on board an aircraft rests on the proper function of a little black box. The environment of electronic package compartments is carefully controlled to provide the most ideal conditions that can be achieved. The degree to which such sensitive equipment is exposed to corrosive agents is very small, but even small quantities of moisture and contaminants can adversely affect equipment reliability. Components in these areas should be inspected for corrosive attack as thoroughly as possible during routine checks, and advantage should also be taken of nonscheduled component removals for further inspection.
Chap 7 Par 23 Page 17
AC 20-82 5 Dec 72
26. CONTROL CABLES. Control cables have preservative coatings which, when intact, prevent corrosive attack. Due to their vital function it is necessary to inspect these cables frequently to ensure that they are adequately protected. During these inspections incipient failures due to other causes also may be detected. It is recommended that control cables be inspected periodically, then cleaned and treated as necessary before reapplication of the preservatives.
27. MICROBIOLOGICAL FUEL CONTAMINATION AND CORROSION. Microbiological contamination in turbine fuel is caused by bacteria and fungi which feed on the constituents of the turbine fuel. The result is a sludge, or mat deposit, which has been found in some aircraft fuel tanks and is often loosely referred to as green slime. However, some deposits have been found in various shades or grey, brown, red, and white. li allowed to develop and grow in the aircraft fuel tanks, microbiological contamination can cause a myriad of problems not the least of which is severe aluminum alloy corrosion in the aircraft integral fuel tanks or the deterioration of the inner liner in fuel bladder cells.
Fairchild Hiller Service Letters FH-227 28-2 dated 15 May 1966 and F-27 222 dated 24 June 1960 are related to this problem.
Chap 7 Page 18 Par 26
5 Dec 72 AC 20-82 CHAPTER 8. MAINTENANCE INFORMATION
28. F-27/FH-227 AIRCRAFT MAINTENANCE INFORMATION. The following is a listing of significant maintenance difficulties that have been reported by air carriers as mechanical reliability reports from January 1970 through June 1971 ADP records. This information may be useful in identifying additional structural inspection problem areas. In all cases, check the corresponding trouble area, leftright, top-bottom, forward-aft, etc.
a. Wing.
(1) During routine inspection, found 1/4-inch crack, left wing at No. 1 tank plate. Crack started from nut plate rivet hole under rivet head, W/S 196 aft of No. 7 stringer.
area had been inspected by X-ray approximately 104 hours prior to discovery of crack but was not visible on X-ray.
(2) During X-ray inspection, found 1/4-inch to 1/2-inch cracks in stringers No. 2, No. 3, No. 4, No. 7 and No. 8, wing center section at W/S zero.
b. Fuselage•
(1) Routine inspection disclosed intergranular corrosion on cockpit floor between F/S 77 and 97. The damaged area was left and right of the center line.
(2) During routine inspection, found intergranular corrosion on the floor panel between F/S 576 and 588 at approximately the center line of the fuselage. The aircraft total time was 12,180 hours.
(3) Routine inspection revealed a 1/2-inch crack in skin and a 3/8-inch crack on the fuselage former flange at F/S 803, right-hand side at stringer No. 168. Total airframe time
(4) Inspection disclosed a 3/8-inch skin crack and 3/4-inch fuselage former crack at F/S 834, right side at stringer No. 168. Total airframe time was 25,238 hours.
(5) Routine inspection disclosed fuselage former at F/S 404 had a 2-inch crack on the right side and two 1/2-inch cracks on the left side. Total airframe time was 29,125 hours.
(6) One report was received concerning loss in flight of a 15- inch by 30-inch section of the right wing-to-fuselage fiberglass fillet.
Chap 8 Par 28 Page 19
AC 20-82 5 Dec 72
c. Flight Controls - Empennage.
(1) Operator reported finding cracks in stringers, ribs, and brackets in the vertical stabilizer VOR antenna mounting area at vertical stabilizer station 201.56. Total time on the aircraft concerned ranged from 7,798 hours to 9,888 hours.
During routine overhaul inspection, a 5/8-inch crack from the bolt hole to the edge of the casting, P/N 27-233000-31, was found in the forward leg of the left rear vertical stabilizer attach casting. Total aircraft time was 14,704 hours.
(3) One operator conducted a fleet campaign and increased inspection frequency as a result of finding a 2-inch crack in the right elevator spar web at the 0/B hinge bracket attachment at elevator station 156. (Ref. Fairchild S/B F-27 27-21 revision No. 3 dated 26 May 1962).
During approach for landing, the crew reported a sharp jerk of the elevator controls. After landing, inspection revealed a hinge bracket broken out from the elevator spar. The bracket was P/N 27-220001-141. Elevator time since overhaul was 1,855 hours.
d. Landing Gear.
(1) Several operators reported finding cracked MLG drag strut end fittings; lower fitting, P/N 200259-302, and upper fitting, P/N 200259-611. Cracks originated at the retaining pin holes.
Total time in service of end fittings ranged from 8,278 hours to 9,764 hours.
(2) The crew reported a loud bang from the nose wheel well after takeoff when gear retracted and nose gear position indicator showed nose gear down. Subsequent inspection disclosed link rod to NIG door lock was broken.
(3) During routine inspection, six loose rivets were found at MLG support angles for retract cylinder attach fittings, P/N 01-502033-41.
(4) The crew reported vibration in the nose section. Ground personnel verified the nose gear was up but one nose gear door was open. Inspection, after landing, revealed the left door attach arm, P/N 27-422013-5, was broken.
Chap 8 Page 20 Par 28
5 Dec 72 AC 20-82
e. Miscellaneous.
(1) One operator experienced a shattering of the left outer windshield panel during cruise. The total time since new was 7,317 hours.
(2) One report of R/H cockpit sliding window shattering during flight was received. Total time in service was 20,782 hours.
(3) An engine gearbox failure resulted in an in-flight shutdown and an unscheduled landing. Subsequent investigation disclosed that the input bevel pinion splines, P/N 601013-329, and blower spur wheel, P/N 601013-284, had failed. Gearbox time since overhaul was 3,363 hours.
Chap 8 Par 28 Page 21 (and 22)
5 Dec 72 AC 20-82 CHAPTER 9. FH-227 AIRCRAFT WINDSHIELD FRAME 29% MAGNETIZATION CHARACTERISTICS. The windshield frame on the FH-227 is made of ferrous metal; thus the windshield frame becomes magnetized if the aircraft has an electrical discharge during an electrical storm. This, in turn, causes erroneous readings on the standby magnetic compass. The windshield, particularly the center post, should be checked periodically for being magnetized.
The windshield can be degaussed.
Chap 9 Par 29 Page 23
Appendix 1 STATION 206 STR LAMINATION STEP #4 ½" NO 5
TOP VIEW FWD ISTR OUTBOARD NO 6 LAMINATION STEP #3 11" NO 7 STATION 197 FIGURE 1. CRACKS IN WING FUEL ACCESS DOOR LAND AT WS 197 AND WS 206.
On a routine inspection of an FH-227 series aircraft, two cracks, ·-inch long each, were found in the No. 1 fuel access door land screw-holes (Ref. Fairchild Hiller Service Bulletin FH 227-51-1). Total aircraft time 12,830 hours. Time since inspection 150 hours. Time since last x-ray 465 hours.
Appendix 1 STA. 195 STR LOOKING AT EDGE TO DETERMINE NO 5
NUMBER OF LAMINATIONS CRACKED CRACK APPROXIMATELY 11" AT LEAST 4 LAMINATIONS
TOP VIEW FWD.
ISTR
OUTBOARD OTNO LOOKING AT EDGE TO DETERMINE•
NUMBER OF LAMINATIONS CRACKED
ALL LAMINATIONS CRACKED APPROXIMATELY 7/8" STR NO 7 STA. 196 FIGURE 2. CRACKS IN WING FUEL ACCESS DOOR LAND AT WS 195 AND WS 196.
On a routine inspection of an FH-227 series aircraft, two cracks, 1/2-inch and 7/8-inch long, were found in the left outer wing panel at the screwholes in the No. 1 fuel access door land. (Ref. Fairchild Hiller Service Bulletin FH-227-51-1). Total aircraft time 12,257 hours. Time since inspection 132 hours. Time since last X-ray 1,143 hours.