Altimeters

BASIC INSTRUMENT PROCEDURES

CHAPTER ONE

AAU-19/A SERVO Altimeter (2F101 Simulator). The AAU-19/A counter-drum-

pointer servo altimeter (Figure 1-1) consists of a pressure altimeter combined with an

AC powered servomechanism. The altimeter has a primary (servo) mode and a

standby (pressure mode) of operation, controlled by a spring-loaded self-centering

mode switch placarded RESET and STBY. In the primary (servo) mode, the

altimeter displays altitude, corrected for position error, from the synchro output of the

altitude computer. In the standby mode of operation, the altimeter displays altitude

directly from the static system (uncorrected for position error) and operates as a

standard pressure altimeter. A DC powered internal vibrator is automatically

energized while in the standby mode to minimize friction in the display mechanism.

AAU-34B/A Solid-State Barometric Altimeter (T-2C Aircraft). All VT-86 T-2C

aircraft are equipped with the AAU-34B/A Solid-State Barometric Altimeter (Figure

1-1). This altimeter is functionally similar to the AAU-19/A, but incorporates a direct

digital reading of altitude by means of a liquid crystal display.

The servo-driven pointer used by the AAU-19/A altimeter has been retained to

provide analog rate information and redundant altitude information between 100-foot

levels. The AAU-34B/A incorporates a vibrating cylinder system similar to that in

the AAU-19/A to minimize friction in the analog display system. The baroset knob

of the AAU-34B/A is used to insert barometric pressure and is used to select between

inches of Hg and millibars. The altimeter has a primary and a standby (pressure)

mode similar to the AAU-19/A. The primary mode of operation is the NORMAL

mode analogous to the RESET mode of the AAU-19/A. The standby mode of

operation uses a solid-state pressure sensor to provide altitude information. The

AAU-34B/A altimeter uses LCD readout rather than a mechanical counter. There is

no altimeter lag inherent in aircraft equipped with this system. Operation of the

AAU-34B/A is functionally identical to the AAU-19/A with the exception that the

primary mode of operation is labeled NORMAL instead of RESET.

NOTE

The AAU-34B/A requires 115-Vac power. In the event of a

complete electrical failure, the altimeter will not display digital

altitude information, and the servo-driven pointer will freeze.

BASIC INSTRUMENT PROCEDURES 1-9