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MIL-PRF-83419 Altimeter, Servo Controlled, Automatic Pressure StandbyThis specification covers integrally-lighted altimeters that have an electromechanically servo driven pointer and a digital display of corrected altitude. The altimeters operate in the normal mode to display altitude transmitted by altitude computers or central air data computers. The altimeters incorporate an integral pressure sensor with electronic outputs to aid operation in the normal mode and to provide altitude inputs for the electronic display of pressure altitude when operated in the standby mode. The altimeters also incorporate an electrical output of barometric pressure setting which is required by some aircraft. A method is provided on the bezel of the altimeter for the selection of barometric setting to be displayed in either inches of mercury \(in. hg\) or millibars \(mb\). The altimeters are designed to operate from the following power sources: 115V, 400Hz \(primary\), 28V DC \(secondary\), and 18V DC \(battery mode\) from an optional rear mounted battery module. Altimeters meeting the requirements of this specification are interchangeable with AAU-19/A, AAU-19A/A, and AAU-19B/A, AAU-34/A, and AAU-37/A Altimeters.

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MIL-PRF-83419E
3.5.12.1.1 Control lever (altimeter arming). The control lever shall also be used to arm
the battery module equipped altimeter. Battery power discharge shall be inhibited when the
altimeter is energized by normal aircraft power. Selecting the standby mode of operation and
holding the control lever in the standby position for 2 seconds prior to release shall arm the
altimeter. Holding the control lever in the direction for selection of normal operation for 3
seconds shall disarm the altimeter.
3.5.12.2 Standby mode indication. A display or flag to indicate the STBY (standby)
mode of operation shall be provided against a yellow background that is in high contrast with the
altitude display. The indication or flag shall not be visible when the altimeter is operating in the
normal mode, but shall clearly indicate STBY when the instrument automatically reverts to the
standby mode in the event a failure is detected or when the standby mode is selected by means of
the control lever. When the altimeter is operating in the normal mode employing 115V 400Hz
electrical power, the standby flag or indication shall not come into view in the event of loss of
aircraft 28V DC power to the instrument.
3.5.12.3 Normal mode indication. When the normal mode is activated by means of the
control lever, the standby flag or indication shall not be visible.
3.5.12.4 Altimeter armed and disarmed indications. When the altimeter is initially
armed by holding the standby/normal control lever to the standby position for two seconds, the
letter "A" shall be displayed to the left of the 10,000 foot digit of the digital altitude display as
shown by FIGURES 4 and 5. The letter "A" shall remain visible for a period of ten minutes
before the altimeter is automatically disarmed unless it is disarmed during this time period by
holding the standby/normal control lever to the normal position for three seconds. Operation of
the altimeter shall continue in the standby mode using aircraft power during this period. Arming
the altimeter shall not prevent the altimeter from being set to the normal mode during this period
or prevent resetting to the standby mode by disarming the altimeter.
3.5.12.4.1 Control lever - disarm. When the control lever is used to disarm the altimeter,
the letter "A" on the display shall not remain visible. In the event of loss of all aircraft power to
the altimeter during the ten minute armed period, the altimeter shall automatically revert to
standby operation using battery power only. The letter "B" above the 1,000 foot digit shall then
be visible as shown in FIGURES 4 and 5 to indicate that the altimeter is operating on battery
power. When initially arming the altimeter, the digital display shall indicate the letters "B Err" if
the altimeter detects that the battery state-of-charge counter has expired. The thousands of feet
digit shall be used to display the letter "B" and the hundreds of feet digits shall display the letters
"Err". When no external power is available, holding the control lever to the standby position for
three seconds shall result in operation of the altimeter in the standby mode. The letter "B" shall
also be displayed. Holding the control lever to the normal setting position for three seconds
during operation when no external power is available shall result in a display of the word "OFF"
on the digital display prior to automatically turning off battery power to the altimeter.
3.5.12.5 Digital altitude display and pointer relationship. The display shall be designed
to provide a direct reading five digit presentation of altitude in feet. The two digits to the left of
the pointer hub shall indicate 10,000 foot and 1,000 foot altitude levels respectively. The three
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