A Altimeters.

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MIL-PRF-83419E

provided with a cover that can be readily removed for installation of a battery module as required

for some applications. Operation and performance of the altimeter with 115V, 400Hz and/or

28V DC electrical powers shall not be affected by operation of altimeters without a battery

module installed or the failure of an installed battery module on battery-equipped altimeters.

Battery-related BIT test and arming displays of the altimeter shall be inhibited when a module is

not mounted on the altimeter. The altimeter outline dimensions and the external connections of

the altimeter shall conform to FIGURE 1.

3.5.1.1 Body (altimeter). Unless otherwise approved by the procuring activity, the case

body and mounting flange shall be made of lightweight, non-magnetic metal, uniform in texture

and have a smooth surface with a durable black finish. The mounting flange of the body shall

have a durable lusterless finish, Color No. 37038 of FED-STD-595. The rear surfaces of the two

upper mounting flanges and the region identified on FIGURE 1 shall be free of paint and shall be

tin plated in accordance with either ASTM-B545 or ASTM-B339, referencing MIL-STD-865 for

guidance, to allow electrical grounding to the aircraft instrument panel and to comply with MIL-

STD-464 requirements. The surface area on the back of the case as shown in FIGURE 1 shall

also be plated to provide for electrical bonding of the altimeter to a battery module.

3.5.1.2 Bezel. The bezel of the case shall be made of nonferrous low-density metal and

shall have a durable lusterless black finish, Color No. 37038 of FED-STD-595. The bezel shall

be held in place by means of screws properly secured by lock washers or similar devices of a

design approved by the procuring agency.

3.5.2 Cover glass, lighting wedge and displays. The cover glass shall conform to

MS28105 and shall not interfere with the readability of the instrument. The glass shall be

properly sealed and direct metal contact with the glass that could result in damage during service

use shall not be made. If lighting wedges are used, they shall be replaceable as an assembly.

Provisions shall also be made for alignment of the lighting wedge assembly to facilitate

overhaul. If the cover glass is used as part of the lighting system, a glass may be used that

deviates from the glass specified herein to the extent required for the lighting function, provided

it does not interfere with the readability of the instrument. Provisions shall also be made for

procurement and replacement of individual wedges in a wedge assembly. Wedge assemblies

shall be interchangeable. All reflecting glass and transparent element surfaces shall be provided

with a reflection-reducing coating, reference MIL-C-14806 for guidance. The distance between

the inner surface of the cover glass and the dial shall be as small as practicable, and shall not

exceed 0.156 inch. The use of plastic lighting elements shall be justified and requires the prior

approval of the procuring agency. Protective measures shall also be taken to reduce any glare or

reflection from the digital display elements.

3.5.3 Integral lighting. AAU-34B/A altimeters shall be integrally lighted with both red

and white lighting circuits as shown in FIGURE 2. The red lighting shall be in accordance with

MIL-L-25467. The white lighting shall be "blue filtered", referencing MIL-L-27160 for

guidance, except the color tolerance shall be �0.03 and the average luminance for the liquid

crystal display shall be 1.5 � .5FL. AAU-34C/A altimeters shall be of the same design as AAU-

34B/A altimeters and meet the requirements for "blue filtered" white lighting, referencing MIL-

L-27160 for guidance, except the color tolerance shall be �0.03 and the average luminance for