should be considered, unless the condition causing the error can be removed permanently.

(iii) Erratic indications of magnetic indicator. If severe deviations are encountered, they may be due to iron or steel items being carried in the aircraft, and located too close to the magnetic direction indicator. Caution must be taken to properly locate articles of this nature away from the vicinity of the indicator.

§ 18.30-14 Engines and fuel systems (FAA policies which apply to § 18.30).

(a) Engines. In repairing or overhauling aircraft engines, all repair agencies should be guided by the recommendations and procedures set forth in the respective instruction books, manuals, or service bulletins for the installation, inspection, and maintenance of aircraft engines, published by the aircraft engine manufacturers for each type of engine. Since many details concerning the repair and overhaul of engines differ decidedly for different types and models of engines, no attempt has been made to include such details in this manual. The overhaul period for aircraft engines used in general service operations should be determined from the manufacturer's recommendations with due consideration given to the condition of each engine involved.

(1) Magnetic, fluorescent penetrant, X-ray, supersonic, and hydrostatic inspections. All rotating, reciprocating and other highly stressed parts of all aircraft engines should be subjected to critical inspection at the time of overhaul. This inspection should be supplemented by any of the following procedures whenever recommended in the pertinent engine manufacturer's overhaul or instruction manuals or by FAA directives:

(i) Wet or dry magnetic dust inspection of magnetic materials;

(ii) Wet or dry penetrant inspection of nonmagnetic materials;

(iii) X-ray or supersonic inspection of any material;

(iv) Hydrostatic inspection of bulky parts and assemblies, such as cylinder heads and cylinders.

A copy of the report of the findings of any of these inspections should be appended to the original repair and altera

tion form in the case of a major repair. Refer to § 18.30-8 (d) (1) through (6) for process details.

(2) Rebuilt engines. A rebuilt engine is defined as a used engine which has been completely disassembled, inspected, repaired as necessary, reassembled, tested, and approved in the same manner and to the same tolerance and limits as a new engine. Component parts of such engines may be either used parts or new parts. The used parts may be either the parts from the same engine or from other service engines, but they must conform to production drawing tolerances and limits to which new parts must conform. In addition, all parts, either new or used, meeting approved oversize and undersize dimensions acceptable for new engines, are also eligible.

(3) Crankshafts. Crankshafts should be carefully inspected for misalinement and if bent beyond the manufacturer's permissible limit for service use, should not be repaired, but should be replaced. Worn journals may be repaired by regrinding in accordance with the manufacturer's instructions. If the original fillets are altered at any time, their radii should not be reduced and their surfaces should be polished free of all tool marks. No attempt should be made to straighten crankshafts damaged in service without consulting the engine manufacturer for appropriate instructions. In no case should an attempt be made to straighten a nitrided crankshaft.

(4) Replacement parts in certificated engines. Only engine parts which are approved by the Federal Aviation Agency should be used in making replacements in certificated aircraft engines. This applies also to engine component parts such as magnetos, spark plugs, etc.

(i) Engine parts obtained from war surplus or military stocks are eligible for use providing they are found to meet the prescribed inspection limits; are otherwise in serviceable condition, and were originally acceptable under the military procurement agency's standards.

(ii) Parts for obsolete engines for which new parts are no longer obtainable from the original manufacturer or his successor manufacturer, are sometimes fabricated locally. When it becomes necessary to do this, physical tests and careful measurements of the old part

may provide adequate technical information. However, this procedure is usually regarded as a major change which requires engine testing and is not recommended except as a last alternative. Oftentimes, FAA engineering data is available in Washington for obsolete engines and it may be useful in providing information for the foregoing purpose.

(5) Cylinder hold-down nuts and cap screws. Great care is required in tightening cylinder hold-down nuts or cap screws. They must be tightened to close torque limits to prevent improper prestressing and to insure even loading on the cylinder flange. The installation of baffles, brackets, clips, and other extraneous parts under these nuts and cap screws is not considered good practice and should be discouraged. If these baffles, brackets, etc., are not properly fabricated or made of suitable material, they will cause loosening of the nuts or cap screws even though the nuts or cap screws were properly tightened and locked at installation. Either improper prestressing or loosening of any one of these nuts or cap screws will introduce the danger of progressive stud failure with the possible loss of the engine cylinder in flight. Never install parts made from aluminum alloy or other soft metals under cylinder hold-down nuts or cap

screws.

(6) Run-in time. After an aircraft engine has been overhauled, it should be run-in in accordance with the pertinent aircraft engine manufacturer's instructions. If no special test stand, test club, and other equipment are available, the engine may be run-in on the aircraft and the aircraft should be headed into the wind during the run-in on the ground so that the maximum cooling effect will be obtained. Proper cooling during run-in cannot be overemphasized. The manufacturer's recommendations concerning engine temperatures and other criteria should be carefully observed.

may be used on aircraft engines provided the following criteria are met:

(i) Where their use is specified by the engine manufacturer in his assembly drawing, parts list, and bills of material which are approved by the Federal Aviation Agency.

(ii) When the nuts will not fall inside of engine should they loosen and come off.

(iii) When there is at least one full thread protruding beyond the nut.

(iv) If cotter pin or locking-wiring holes are in the bolt or stud, the edges of these holes should be well-rounded to preclude damage to the lock nut.

(v) The effectiveness of the self-locking feature should be checked and found to be satisfactory prior to its re-use.

(vi) Engine accessories should be attached to the engine by means of the types of nuts furnished with the engine. On many engines, however, self-locking nuts are furnished for such use by the engine manufacturer for all accessories except the heaviest, such as starters and generators.

(vii) On many engines, the cylinder baffles, rocker box covers, drive covers and pads, and accessory and supercharger housings, are fastened with fiber insert locknuts which are limited to a maximum temperature of 250° F. inasmuch as above this temperature the fiber will usually char and consequently lose its locking characteristic. On locations such as the exhaust-pipe attachment to the cylinder, a locknut which has good locking features at elevated temperatures will give invaluable service. In a few instances, fiber insert locknuts have been approved for use on cylinder holddown studs. This practice is not generally recommended since especially tight stud fits to the crankcase must be provided, and extremely good cooling must prevail so that low temperatures exist at this location on the specific engines for which such use is approved.

(viii) It is necessary that all proposed applications of new types of locknuts or new applications of currently used selflocking nuts must be investigated adequately since most engines require some specially designed nuts. Such specially designed nuts are usually required for one or more of the following reasons: (a) To provide heat resistance;

(b) To provide adequate clearance for installation and removal;

(c) To provide for the required degrees of tightening, or, locking ability which sometimes require a stronger, specially heat-treated material, a heavier crosssection, or a special locking means;

(d) To provide ample bearing area under the nut to reduce unit loading on softer metals;

(e) To prevent loosening of studs when nuts are removed. Information concerning approved self-locking nuts and their use on specific engines is usually found in engine manufacturer's manuals or bulletins. If the desired information is not available, it is suggested that the engine manufacturer be contacted.

(9) Designating converted engines. When engine type of model conversions are accomplished (see § 18.1-1 (b) (2)), the engine nameplate should be altered or replaced to include the new official model designation and any other necessary information shown on the pertinent FAA engine specification.

(i) For current engines, information concerning engine modernizing, engine model conversions, and new properly marked nameplates should be obtained from the engine manufacturer.

(ii) For military surplus engines, or old engines for which new nameplates can no longer be secured, the new model designation symbols should be marked, either in the same title block adjacent to the old symbols, or on a plain thin steel plate attached beside the existing plate by at least two of the mounting screws. For engines which were never provided with separate designation plates and have, instead, an integral stamping boss on the crankcase, the new designation symbols should be added thereto, or a stamped thin steel plate may be fabricated and attached thereto. The superseded model designations should be obliterated or enclosed with parentheses. When metal stamps are used, care should be exercised to avoid damage to the engine.

(iii) In some instances, suffix letters should be added to the engine serial number on the nameplate to designate certain alterations or conversions. Such additions should be made when the alteration or conversion is not of sufficient importance to warrant model designation changes. Examples of these letter additions are:

(a) Suffix letter "C" on P & W Military R-2000-7 and -11 engines denoting the

plain main bearing type main crankcases as indicated on Specification 5E-5;

(b) Suffix letters "A," "E," "L," "M," or "P" on Warner Super Scarab Series 50 engines as indicated on Specification E104;

(c) Suffix letter "D" on Continental E185 series engines denoting incorporation of a dampered crankshaft as indicated on Specification E-246.

(iv) Examples of model designation changes are:

(a) Pratt and Whitney R-985-AN-1 engine converted to R-985-AN-14B may be redesignated R-985-AN-(1) 14B if it is desired to preserve its former designation. Usually, though, there is no specific reason to preserve prior identities of converted engines.

(b) A Continental A-65-8 engine converted to an A-75 engine with flangetype crankshaft should be redesignated an A-75-8F engine. Continental Service Bulletin No. M47-16 discusses the manufacturer's recommended procedures for handling conversions of Continental engines.

(c) A Wright R-1820-71 engine, when installed in certificated aircraft, should be redesignated with its civil model designation 702C9GC1 and Type Certificate No. 219. Similarly, a Lycoming O-235-2 engine nameplate should be redesignated O-235-B and Type Certificate No. 229.

(d) An R-1830-65 engine, when converted to an R-1830-90D engine, may be designated R-1830-90D and the "65" obliterated.

(v) Some model conversions merely require the addition of the symbols M1 or M2, etc., to the existing designation, e. g., R-2000-7M1 as indicated on Specification 5E-5.

(10) Welding in the repair of engines (1) General. In general, welding of highly stressed engine parts is not recommended. However, under the conditions given below, welding may be accomplished if it can be reasonably expected that the welded repair will not adversely affect the airworthiness of the engine:

(a) When the weld is externally situated and can be inspected easily;

(b) When the part has been cracked or broken as the result of unusual loads not encountered in normal operation;

(c) When a new replacement part of obsolete-type engine is not available;

(d) When the welder's experience and equipment employed will insure a first quality weld in the type of material to be repaired and will insure restoration of the original heat treat in heat-treated parts. Also refer to § 18.30-4 (b) for information on process details.

(ii) Welding of minor parts. Many minor parts not subjected to high stresses may be safely repaired by welding. Mounting lugs, cowl lugs on cylinders, covers, etc., are in this category. The welded part should be suitably stressrelieved after welding.

(11) Metallizing. Metallizing should not be done on any internal part of an aircraft engine except when it is proved conclusively to the Federal Aviation Agency that the metallized part will not adversely affect the airworthiness of the engine. Metallizing the finned surfaces of steel cylinder barrels with aluminum may be accomplished since many engines are originally manufactured in this

manner.

(12) Plating-(i) General. Plating may be restored on an engine part when accomplished in accordance with the manufacturer's instructions.

(ii) Plating of highly stressed parts. In general, chromium plating should not be applied to highly stressed engine parts. Certain applications of this nature have been found to be satisfactory. However, the processes to be used should be approved in all details by the Federal Aviation Agency. Porous chromiumplated cylinder walls have been found to be satisfactory for practically all types of engines. Dense or smooth chromium plating without roughened surfaces, on the other hand, has not been found to be generally satisfactory. For cylinder bore chromium plating, FAA engineering approval of the process used is required. Information with respect to what agencies are approved for this work may be obtained from the FAA. Dense chromium plating of the crankpin and main journals of some small engine crankshafts has been found to be satisfactory except where the particular crankshaft is already marginal in strength. Refer to § 18.30-7 (b) (2) for further information on plating.

(iii) Plating of minor parts. Plating, including chromium plating, may be utilized to restore worn low-stressed engine parts, such as accessory drive shafts and splines, propeller shaft ends, and the

seating surfaces of roller- and ball-type bearing races.

(13) Corrosion prevention. The application of corrosion preventive measures for temporary and dead storage, preservation, pickling, etc., should be accomplished in accordance with instructions issued by the pertinent engine manufacturer. The use of strong solutions which contain strong caustic compounds and of all solutions, polishers, cleaners, abrasives, etc., which might possibly promote corrosive action, should be avoided. Refer to § 18.30-7 for further details.

(14) Engine accessories. Engine accessories should be overhauled and repaired in accordance with the recommendations of the engine manufacturer and the accessory manufacturer.

(b) Fuel systems—(1) Fuel tanks. Welded or riveted fuel tanks that are made of commercially pure aluminum, 3S, 52S, or similar alloys, may be repaired by welding. Tanks made from heattreatable aluminum alloys are generally assembled by riveting. In case it is necessary to rivet a new piece in place, the patch should be of the same material as the tank, and a sealing compound that is insoluble in gasoline should be used in the seams. If aromatic fuels are used, special sealing compounds which are resistant to aromatic fuels should be employed.

(i) Removal of flux after welding. It is especially important, after repair by welding, to completely remove all flux in order to avoid possible corrosion. Therefore, promptly upon completion of welding, the tank should be washed both inside and outside with liberal quantities of hot water, and drained. Next, immerse it in either 5 percent nitric or 5 percent sulfuric acid, or fill the tank with this solution (in which case also wash the outside with the same solution). Permit this acid to remain in contact with the weld about 1 hour and then rinse thoroughly with clean fresh water. efficiency of the cleaning operation may be tested by applying some acidified 5 percent silver nitrate solution to a small quantity of the rinse water that has been used to last wash the weld. If a heavy white precipitate is formed, the cleansing has been insufficient and the washing should be repeated.

The

(2) Fuel tank caps, vents, and overflow lines. Fuel tank caps should be inspected as to the integrity of the gas

ket, and vents should be inspected to ascertain that they are clear. Overflow lines should be inspected to ascertain that the integrity of the material and connections are satisfactory. Care should also be taken to ascertain that the vent exit is in proper position.

(3) Fuel lines. Aluminum or aluminum alloy tubing should not be annealed after forming or at overhaul periods as is required practice with copper tubing. Fuel lines should be thoroughly inspected for integrity of end fittings, for bends or kinks beyond recommended bend radii, for foreign material within the lines, and for integrity of the material which could be affected by abrasion, acid, heat, or swelling in the case of rubber impregnated lines. Too sharp bends or kinks, evidence of excessive heat, abrasion, or a change in the material are causes for replacement.

(4) Fuel strainers and sediment bowls. The adjusting nut located at the bottom of the bowl of the fuel strainer should be positively safetied in position. This nut should be tightened only with the fingers. If leakage still occurs, do not tighten with pliers but replace the cork gasket between the glass bowl and the screen. The screens of all strainers should be periodically inspected for foreign material or rupture. Screens should only be replaced by those recommended by the manufacturer as the mesh size affects the fuel flow through them. Sediment bowls should be given frequent inspections for water or solid material. § 18.30-15 Propellers (FAA policies which apply to § 18.30).

(a) Inspection of propellers-(1) General. The propeller is easily accessible for visual inspection and should always be checked before a flight to determine that no damage has occurred. Propellers should be inspected periodically as recommended or required by maintenance manuals, service bulletins, and airworthiness directives.

(2) Wood or composition propellers and blades. Due to the nature of the wood itself, it is necessary that wood propellers and blades be inspected frequently to assure continued airworthiness. They should be inspected for such defects as cracks, bruises, scars, warp, evidence of glue failure and separated laminations, sections broken off, and defects in the finish. Composition blades must be handled with the same consideration as wood blades.

(i) The fixed-pitch propeller should be removed from the engine at engine overhaul periods. Whenever the propeller is removed, it should be visually inspected on the rear surface for any indication of cracks. When any indications are found, the metal hub should be disassembled from the propeller. The bolts should be inspected for wear and cracks at the head and threads and, if cracked or worn, should be replaced with new AN bolts. The propeller should be inspected for elongated bolt holes, enlarged hub bore, and checks or cracks inside of bore or anywhere on the propeller. Propellers found with any of these defects should not be used until repaired. If no defects are found, the propeller may be reinstalled on the engine. It should first be touched up with varnish at all places where the finish is worn thin, scratched, or nicked. Track and balance the propeller, and coat the hub bore and bolt holes with some moisture preventive such as asphalt varnish. In case the hub flange is integral with the crankshaft of the engine, final track should be made after the propeller is installed on the engine. In all cases where a separate metal hub is used, final balance and track should be accomplished with the hub installed in the propeller.

(ii) On new fixed-pitch propeller installations the hub bolts should always be inspected for tightness after the first flight and after the first 25 hours of flying. Thereafter, the bolts should be inspected and checked for tightness at least every 50 hours. No definite time interval can be specified, since bolt tightness is affected by changes in the wood caused by the moisture content in the air where the airplane is flown and stored. During wet weather, some moisture is apt to enter the propeller wood through the drilled holes in the hub. The wood swells but, since expansion is limited by the bolts extending between the two flanges, some of the wood fibres are crushed. Later, when the propeller dries out during dry weather or due to heat from the engine, a certain amount of propeller hub shrinkage takes place and the wood no longer completely fills the space between the two hub flanges. Accordingly, the hub bolts become loose.

(iii) In-flight tip failures may be avoided by frequent inspections of the metal cap and leading edge strip, and the surrounding areas. Inspect for such defects as looseness or slipping, separation