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to electric cable terminals. Tubular members should be bonded by means of clamps to which the jumper is attached. Proper choice of clamp material, to match the tube material, will minimize corrosion.

(3) Ground return connections. When bonding jumpers will carry substantial ground return current, it should be determined that the current rating of - the jumper is adequate, and that a negligible voltage drop is produced.

(4) Insulation of electrical equipment from ground. In some cases, a unit of electrical equipment is connected into a heavy current circuit, perhaps as a control device, or relay. Such equipment should be insulated from the mounting structure, since grounding the frame of the equipment may result in a serious ground fault in the event of internal failure of the equipment. If a ground connection for a control coil must be - provided, a separate small-gage wire may be used.

=(h) Anti-collision light installations. Installation of anti-collision lights' should be accomplished in accordance i with the following:

(1) Color. The color of the anti-collision light should be aviation red."

(2) Performance. The flash frequency should be between 40 and 100 flashes per minute. Where two lights are used (one on top and the other on the bottom of the aircraft) the flash frequency in the overlap region may exceed 100 flashes per minute. In all cases, the on-off ratio of the flash should not be less than 1:75.

(3) Location. The anti-collision light should be located on top of the fuselage or vertical tail where obstruction to the light rays is least. If no top fuselage or vertical tail location is practicable without an adverse effect on crew vision, a bottom fuselage location is permissible.

(4) Crew vision interference. Irrespective of location, direct or reflected

1 This policy applies only to aircraft for which an application for type certificate was received prior to April 1, 1957. Subsequent type certificated aircraft are governed by the pertinent Civil Air Regulations effective April 1, 1957.

Aviation red is defined in the Civil Air Regulations as the color which has the International Commission on Illumination chromaticity coordinates below:

y is not greater than 0.335
z is not greater than 0.002

light rays (from propeller disc, nacelle, or wing surface) should not interfere with crew vision. Acceptable methods of preventing such interference include:

(i) Masking of the light assembly to block undesired light output. Masks for this purpose should be of a permanent type.

(ii) Application of non-reflective surface finishes on surfaces which present a reflection problem.

A night flight check should be performed by at least a private pilot (appropriately rated for the aircraft) to assure that any objectionable interference has been eliminated. A notation to that effect should be entered by this pilot in the aircraft log.

(5) Electrical modification—(i) Wiring practice. For general wiring practice information, refer to paragraphs (a) through (g) of this section.

(ii) Circuit protection. A circuit breaker or fuse should be installed as near as practicable to the main bus. The rating of this protective device should be such as to prevent overheating of the wire serving the anti-collision light. A five ampere fuse or circuit breaker will protect AN20 gage copper wire; a ten ampere fuse or circuit breaker will protect AN18 and AN16 copper wire.

Anti-colli

(iii) Generator capacity. sion lights require up to 100 watts of electric power for their operation. On smaller aircraft, this could be a significant percentage of the total generated power, such that the generator may no longer be capable of recharging the storage battery. The criterion for adequate generator capacity on small aircraft is contained in paragraph (i) of this section. In all cases, the electric power system, during any probable operating condition, should be capable of supplying the additional load without thermal or electrical distress.

(iv) Anti-collision light switch. An individual switch (independent of the switch controlling the position lights) should be installed to permit the crew to switch off the anti-collision light when reflections from haze or overcast become troublesome. The switch should be identified and marked as to method of operation.

(6) Structural modification. (i) The simplest fuselage installation involves attachment of the light to a skin panel and stringers. A reinforcement doubler

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FIGURE A-Typical anti-collision light installation in a skin panel.

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FIGURE B-Typical anti-collision light installation involving a cut stringer.

an acceptable criterion is that the maximum continuous load' on the electrical system should not exceed 80 percent of total generator rating.

On such aircraft, the maximum continuous load may be determined within

'Continuous loads are those which draw current continuously in flight, such as radio equipment and position lights. Occasional intermittent loads (such as landing gear, flaps, or landing lights) are not considered.

reasonable limits by the following 1 method.

(1) First, check the aircraft battery to determine that it is fully charged and in satisfactory condition.

(2) Next, check to determine if an accurate ammeter is installed which measures the current supplied by the battery to the electrical load. An ammeter in the generator feeder wire will not do this. If an accurate ammeter

C

Mounting Screw Holes For Light To Fairing

Note:

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Skin Thickness of Mounting Ring and

Fairing are at Least Equivalent

FIGURE C-Typical anti-collision light installation in a fin tip.

is not provided, it will be necessary to temporarily connect such an ammeter between the battery and the electrical load. An ammeter having an error no greater than 2 percent is acceptable.

(3) Next, with the engine(s) not operating, turn on all equipment which can continuously draw electrical power in flight, such as all radio receivers and transmitters in standby condition, autopilot, navigation lights, instrument lights, pitot heater, cabin heater, electrically driven instruments, and any other electrical equipment which may be required to be used continuously in any cruise condition.

(4) Next, read and record the total amount of current drain indicated on the ammeter. Do not operate equipment any longer than necessary to accurately read the ammeter; otherwise, the battery may discharge below nominal rated voltage.

E (5) Next, add 10 percent to the ammeter reading recorded in the previous step. (This is to compensate for the additional electrical current which results from the higher voltage supplied by the generator.) The ammeter reading plus 10 percent will give the approximate continuous cruise electrical load. For example, if the ammeter reading shows a current drain of 25 amperes, the approximate cruise load would be 25 amperes plus 10 percent of 25, or 27.5 amps.

(6) Next, determine the generator maximum output rating in amperes. Most aircraft generators have a nameplate which shows this rating; however, some generators will show only the nominal voltage of system and model number. In the latter case, the current rating normally can be determined by reference to the aircraft specifications. In some instances, the aircraft specifications will also show only the model number of the approved generator(s). Under such circumstances, it will be necessary to refer to the generator manufacturer's data for the particular model. In any event, the maximum continuous rating of the generator(s) must be determined accurately.

(7) Next, compute 80 percent of the generator rating and determine that the resultant figure is not less than the maximum continuous load. For exampie, 80 percent of a 35 ampere rating is 28 amperes. If the maximum continuous load is found to be 27.5 amperes, as in

the previous example, it obviously will be within 80 percent of the rated output of the generator.

Note that this method applies only when a modification imposes an additional continuous electrical load on the aircraft, and then only when the total capacity of the generator or generators is less than 21⁄2 kw. (21⁄2 kw generator capacity represents 178 amperes capacity for a nominal 14-volt generator system and 89 amperes for a nominal 28volt generator system.) This is strictly a "rule of thumb" method and should not be confused with an electrical load analysis, which is a complete and accurate analysis of the composite aircraft power sources and all electrical loads.

(j) Storage battery installations—(1) Battery installation hazards and means of prevention-(i) Explosion. Electrochemical action in all commercial aircraft storage batteries (lead-acid, nickel-cadmium, and silver-zinc) generates hydrogen. If this hydrogen is released to the surrounding atmosphere, an explosive hydrogen-air mixture may accumulate. Each battery cell generates approximately 7 cc. of hydrogen gas (H.) per ampere-minute as the battery nears full charge. Four percent concentration of hydrogen in air is violently explosive. To provide a margin of safety, the concentration of this gas should be kept below one percent by ventilation which is effective during all flight regimes. The ventilation air flow should be sufficient to cope with any probable charging condition, including those which could result from any malfunction in the charging system. An acceptable method of achieving the necessary ventilation is to enclose the battery in a case which is vented by connection to a point of negative pressure on the aircraft skin. Positive pressure can be added by connecting another vent to a ram-air scoop elsewhere on the aircraft surface. An acceptable alternative would be to locate the battery in a compartment through which sufficient ventilating air naturally flows during flight in such a manner that the hydrogen gas is dumped overboard. Certain nickel-cadmium batteries are so designed that the hydrogen generated within the cell during charging is chemically recombined. If it can be demonstrated that no hydrogen is emitted during any probable charging condition (the probability of over-voltage on the

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