5 Dec 12 AC 20-82 CHAPTER 6. NACELLES
13. F-27/FH-227 AIRCRAFT MAINTENANCE INFORMATION• Following is a listing of significant maintenance difficulties that have been reported by air carriers. in addition, a number of check and inspection items are listed. This information may be useful in identifying structural inspection areas. Except where noted, nacelle structural references apply to both left and right nacelles.
a. Lower Connection Strips. Cracks have been detected in the lower connecting strips at cutout areas of N/S 124, 141, and 157.
b. Nacelle General. Check entire area of center section interior O/B ends for cracks and skin stringers, front and rear spar, and any other evidence of structural irregularity between N/S 120 and 160.
c. Stringers. Check upper center section stringers No. 2 through No. 10 for cracks or other evidence of structural irregularities.
d. Access Doors. Check for cracks in all access doors and door areas.
Premature Cable Wear. Operators have reported premature wear of engine, fuel shutoff, and crossfeed control cables caused by rubbing in fairleads. Applies to aircraft with serial numbers prior to 521.
(Ref. Fairchild Hiller S/B FH-227 54-3 dated 25 April 1967.)
£. Nacelle Aft Bulkhead. On aircraft with serial numbers prior to 522, inspecto for cracks in the rear bulkhead of the left nacelle adjacent to the AC voltage regulator shelf. (Ref. Fairchild Hiller S/B FH-227 54-7 dated 7 June 1967.)
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5 Dec 72 AC 20-82 CHAPTER 7. CORROSION-PRONE AREAS
14. GENERAL Corrosion is most likely to strike at the joints or attachment points in metallic structure because they provide entrapment areas for corrosive agents and moisture to accumulate. However, the problem can be compounded if metallic surfaces are exposed to an extremely corrosive environment, or if the surfaces are difficult to inspect and clean. The most important corrosion preventive measure is to keep them clean and dry.
15. EXHAUST TRAIL AREAS. Both jet and reciprocating engine exhaust deposits contain compounds that are very corrosive, and the structure in the path of exhaust gases is more likely to suffer from corrosion than is any other structure. It is customary to coat structure exposed to exhaust gases with protective finishes to prevent these gases from coming in direct contact with the metal. However, the deposits which collect on top of the protective finishes must be removed before they permeate the film and attack the metal. Most troublesome are those areas where exhaust gas deposits may become entrapped and cannot be reached by normal cleaning methods. Typical of these areas are seams, gaps, hinges, or fairings located in the exhaust gas path.
16. ENGINE FRONTAL AREAS AND COOLING AIR VENTS. These areas are subject to erosion by airborne contaminants, rain, and from foreign objects on the runways. Erosion will remove the protective finishes or oxide film from the metal surfaces leaving them vulnerable to corrosive attack.
recesses is also vulnerable to corrosion. When an aircraft is operated in a marine environment, salt deposits may accumulate in these areas and the ensuing corrosive attack can be rapid and destructive. It is imperative that these areas be frequently inspected and cleaned, and protective finishes be maintained.
17. BATTERY AREAS AND VENTS. Due to the highly corrosive nature of battery acid and its fumes, battery areas and their vents are protected by special acid-resistant paints. Generally this is enough to stem the tide of corrosion if scrupulous attention is devoted to keeping these areas clean.
18. LAVATORIES, GALLEYS AND CABIN FLOORS. The usual spillage, condensation, and other contamination of these areas are extremely corrosive to aircraft metals. The most common corrosive agents are acidic foods and beverages, and human excreta. Also, most chlorinated disinfectants are acidic and corrosive, and cannot be recommended for use in aircraft. It is impractical to assume that these areas can be kept clean and dry at all times, but it is important to inspect Chap 7 Par 14 Page 15
AC 20-82 5 Deç 72 the structure carefully at suitable intervals, cleaning and renewing the finish as necessary. Areas behind lavatories, sinks, or ranges where waste can collect are potential trouble spots, as are personnel relief and waste disposal vents or openings on the exterior of the aircraft.
19. WHEEL WELLS AND LANDING GEARS. Equipment installations in the wheel well areas probably absorb more punishment than any other portion of an aircraft because they are exposed to moisture and flying debris during takeoffs and landings, and when the aircraft is parked they are exposed to atmospheric moisture. After an airplane has entered service, it is difficult to maintain protective paint film on landing gears, equipment installations, and wheel well suriaces because the many complicated shapes, assemblies, and fittings in these areas obscure other surfaces. Items that should receive special attention during wheel well inspections are!
a. Magnesium wheels (especially the areas around the bolt heads, lugs, and wheel webs).
b. Portions of rigid tubing obscured by clamps and identification tapes.
c. Exposed electrical equipment.
d. Crevices between ribs, stiffeners, and lower skin surfaces which can serve as water or debris entrapment areas.
Corrosion control in wheel well areas may best be attained by frequent cleaning, lubrication, paint touchup and judicious use of wheel covers.
20. CONTROL SURFACE RECESSES. Control surface recesses are potential problem areas because normally they are difficult to inspect. If corrosive agents gain entry and accumulate in these areas, they may go unnoticed for some time. Frequent inspection and cleaning of the surfaces and installations located in these recesses will prevent corrosion from gaining a foothold.
21. SPOT-WELDED SKINS. Corrosive agents may become entrapped between the layers of metal adjacent to the spot-weld beads. If moisture enters the area, an elecrolytic cell can be set up between the dissimilar metal phases in the spot-weld area, and one or more of these phases will be subject to preferential corrosive attack. Whenever practical, structural areas with spot-welded assemblies should be sealed to prevent the ingress of contaminants and moisture.
22. HINGES. Hinges are natural traps for corrosive agents. Often they are susceptible to galvanic corrosion when the hinges and pins are made of dissimilar metals. The most practical means of corrosion control is to inspect and lubricate hinges frequently. After lubrication, actuation of the door through several cycles is necessary to ensure complete penetration of the lubricant.
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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.
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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.
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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.
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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.
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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.
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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.
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