charging system should also be investigated), such nickel-cadmium batteries need not be ventilated for the purpose of explosion prevention.

(ii) Noxious fumes. When charging rates are excessive, the electrolyte may boil to the extent that fumes containing droplets of the electrolyte are emitted through the cell vents. These fumes may become noxious to crew and passengers. Closed ventilating systems (in which the battery is enclosed and vented as described in subdivision (i) of this subparagraph) dispose of any caustic or noxious gases which may be emitted by the battery in flight. When the battery is not case-enclosed, but rather located in a ventilated compartment in the aircraft, the ventilating air should be directed away from passengers and crew. Electro(iii) Electrolyte corrosion. lyte spillage or leakage may result in serious corrosion of nearby structure or control elements. Both sulphuric acid and potassium hydroxide are actively corrosive. Electrolyte may be spilled during ground servicing, leaked when cell case rupture occurs, or sprayed from cell vents due to excessive charging rates. A generally satisfactory solution for the leakage problem is to place the battery in a case which can contain the total quantity of electrolyte, or which is provided with an overboard drain. All case and drain surfaces which will come in contact with electrolyte should be treated to prevent corrosion effects. Sprayed electrolyte is normally disposed of by the provisions for closed ventilation. If the battery is not case-enclosed, structural parts near the battery which may be affected should be properly treated. Electrolyte spilled during ground servicing should be neutralized at once with solutions of sodium bicarbonate (for acid electrolyte) or boric acid (for alkaline electrolytes). Residue should be washed off with clean water and the area thoroughly dried.

(iv) Battery overheat failure. Operation of storage batteries beyond their ambient temperature or charging voltage limits will result in excessive cell temperatures leading to electrolyte boiling, rapid deterioration of the cell and finally to battery failure. Maximum electrolyte temperature should not exceed 115° F. for any operating condition. To avoid overheating, locations where high ambient temperatures are encountered (such as engine accessory compart

ments) should be avoided. Convection cooling by special means may be used, if necessary. The relation between maximum probable charging voltage and the number of cells in the battery is also significant, since this will determine (for a given ambient temperature and state of charge) the rate at which energy is absorbed as heat within the battery. For lead-acid batteries the voltage per cell should not exceed 2.35 volts. In the case of nickel-cadmium batteries the charging voltage limit varies with design and construction, with values of 1.4 to 1.5 volts per cell found satisfactory. In all cases, the recommendations of the battery manufacturer as to proper charging voltage limits and minimum cooling provisions should be followed. Where battery cooling is marginal, it is permissible to use a thermostatically controlled relay arrangement to prevent battery overheat. This device should open the circuit between bus and battery when a limit temperature is reached but should reestablish the circuit for emergency service when bus voltage is lost.

(2) Substitution of nickel-cadmium batteries for lead-acid types. Nickelcadmium batteries may replace lead-acid types when their capacity (at the 5-hour rate) is at least 30 percent of the leadacid capacity.

(3) Battery additives and electrolyte replacements. Battery additives or electrolyte replacements may be used if endorsed by the battery manufacturer involved, or if substantiated by a performance test conducted by the user to demonstrate that the additive or replacement will not reduce battery perform

ance.

An acceptable performance test would be to compare the capacity of the battery at the 5-minute, 1-hour, and 5hour discharge rates (using the original electrolyte) with the capacity of the same battery at the same discharge rates using the additive or replacement electrolyte. This test should be conducted¦ at both 0° F. and 75° F. and the additive or electrolyte replacement should be added according to the manufacturer's instructions. If a reduction in performance is noted, the additive or replacement electrolyte is not acceptable.

(k) Circuit protection devices-(1) General. Circuit breakers or fuses should in all cases protect the cable and should be located as close as possible to the source bus.

Matching protector to cable. The t breaker or fuse should open the t before the cable emits smoke. To plish this, the time current charstic of the protective device should elow that of the associated cable. der to obtain maximum utilization e connected equipment, the circuit ctor characteristics should be hed to the cable characteristics as y as possible.

Circuit protector chart. Table No. Appendix B,' may be used as a for the selection of circuit breaker ise rating to protect copper conducble. This chart was prepared for conditions specified by the notes - accompany the chart. If actual tions deviate materially from those 1, ratings above or below the values mended may be justified. For ple, a wire run individually in the air may possibly be protected by a t breaker of the next higher rating at shown on the chart. In general art is conservative for all ordinary aft electrical installations.

Circuit breaker type. (i) All reole type circuit breakers should the circuit irrespective of the posiof the operating control when an pad or circuit fault exists. Such t breakers are referred to as "trip

Automatic reset circuit breakers h automatically reset themselves lically) should not be applied as t protective devices.

313 (a) of Federal Aviation Act of Au13, 1958, 72 Stat. 731, 752 (Pub. Law ). Interpret or apply sec. 601, 72 Stat. [Supp. 1, 18 F.R. 7391, Nov. 21, 1953, ended by Supp. 8, 22 F.R. 3916, June 5, 22 F.R. 4908, July 12, 1957; Supp. 9, 23 718, Mar. 13, 1958; Supp. 11, 23 F.R. Nov. 20, 1958; Supp. 12, 24 F.R. 1279, 9, 1959]

30-13 Instruments (FAA policies which apply to § 18.30).

General (1) Instrument instal· and maintenance. (i) Care

d be taken with instruments to preheir accidental damage.

When instruments do not give r indications, they should be sent approved instrument overhaul and :station or returned to the manurer for servicing.

pendix B not filled with the Office of deral Register.

(2) Vibration insulation. Instruments should not be subjected to excessive vibrations. When shock-insulated panels are used, the mountings should be periodically checked for condition and the panels for alinement. When necessary to replace shock mounts, units of the same characteristics should be used. Only flexible connector tubing should be used to join the ends of lines to the instruments. Care should be exercised to insure that the instrument panel does not contact any parts of the airframe when vibrating normally.

(b) Pitot-static system-(1) System components. The conventional design of the pitot-system consists of pitotstatic tubes or pitot tubes with static pressure parts and vents, lines, tubing, water drains and traps, selector valves, and various pressure actuated indicators or control units such as the altimeter, air-speed and rate of climb indicators, and automatic pilots connected to the system.

(1) Pitot-static tube. The tube should have its axis parallel to the longitudinal axis of the aircraft when in cruising flight configuration. All repairs and alterations on the pitot-static system should be made in conformance with the manufacturer's recommendations.

(ii) Static pressure ports or vents. All alterations or relocations of the static pressure ports or vents should be made in conformance with the aircraft manufacturer's engineering recommendations. (See paragraph (a) (1) of this section and subparagraph (2) of this paragraph.)

In the

(iii) Heater not operative. types of tubes where the electric element is not replaceable, it becomes necessary to replace the tube. The voltage at the heater terminals should not be less than 85 percent of the rated system voltage.

(iv) Clogging of pitot-static tube or static vent drains. If water or obstructive material has entered the system, all drains should be cleaned. The drains in the pitot-static head should be probed with a fine wire to remove dirt or other obstructions. The bottom static openings act as drains for the head's static chamber and these holes should be checked at regular intervals to preclude malfunctioning of the system.

Caution: Make sure all instruments are disconnected during cleaning procedures.

(v) Relocation of pitot-static tube. If relocation of the pitot-static tube is necessary it should be done in accordance with the manufacturer's recommendations and with due consideration of the following:

(a) Freedom of aerodynamic disturbances caused by the aircraft.

(b) Location protected from accidental damage.

(c) Alinement with the longitudinal axis of the aircraft when in cruising flight configuration.

(2) Pitot-static lines—(i) Poor drainage of lines. If drainage is poor, check the line diameter. If this tubing diam

eter is less than three-eighths inch outside diameter, it should be replaced with this size tubing to overcome the difficulty, as water will not drain freely in smaller size lines.

(ii) Replacing the lines. If necessary to replace lines, the following installation practices should be observed:

(a) Attach lines to airframe at regular intervals by means of suitable clamps.

(b) Do not clamp lines at end fittings. (c) Maintain slope of lines toward drains so that proper drainage will be effected.

(d) Use thread lubricant on fittings, preventing excess lubricant from entering lines.

ute, the leakage should not exceed the equivalent of 10 miles per hour.

Warning: Do not apply suction to pitot

lines.

(v) Maintenance of lines. Inspection of the lines should be made periodically. Water accumulation can be removed by opening the drain caps on valves. If the installation is not properly self-drained, disconnect the lines from the instruments and carefully "blow" the lines with clean dry air.

(c) Magnetic direction indicator 18 (compass)-(1) Correction for errors in magnetic direction indicator-(i) Swinging the indicator (ground). When a the magnetic direction indicator does not yield satisfactory directional indications, es it can be calibrated by the "ground swinging" technique as follows:

(a) Remove aircraft to location free from influence of steel structures, underground pipes and cables, reinforced concrete, or other aircraft.

(b) Place the aircraft in level flying position.

(c) Remove compensating magnets from chambers or reset the fixed compensating magnets to neutral positions, whichever is applicable, before swinging.

(d) Check indicator for fluid level and cleanliness. If fluid is required, it should be added before compensation

(e) Check the pivot friction of indicator by deflecting the card with a small magnet. The card should rotate freely in a horizontal plane.

(f) If radio is used in aircraft, there should be corrections noted for "Radio On" and "Radio Off" conditions.

(g) Aline the aircraft with the North magnetic heading and compensate with compensating magnets. Repeat for the East magnetic heading. Then place on South and West magnetic headings and remove half of indicated error by adjusting compensators. Engine(s) should be running.

(h) Turn the aircraft on successive 30° headings through 360°. Placard should be marked to indicate correction at each 30° heading showing "Radio On" and "Radio Off" corrections.

(ii) Indicator cannot be properly compensated. The pilot's indicator should have deviation of less than 10° at any heading. When this maximum is exceeded, a new location for the indicator

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. applies also to engine component parts such as magnetos, spark plugs, etc.

This

(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.

(7) Re-use of safetying devices. Cotter pins and safety wire should never be used a second time. Flat steel-type wrist-pin retainers and thin lock washers likewise should be replaced, but special coil spring or plug-type retainers need not be replaced at overhaul if the manufacturer's recommendations permit

re-use.

(8) Self-locking nuts for aircraft engines and accessories. Self-locking nuts

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 tiber 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;