Air data computers consist of a pressure-
aircraft containing an ADC, the ADC auto-
sensing means, a computing mechanism, an
matically reports altitude. The modification also
error signal generator, a servo loop, and output
provides an output for the AAU-19/A servoed
devices. The output devices provide signals for
altimeter. Slower, low-flying aircraft, not
both altitude indication and altitude reporting.
requiring an ADC, have AAU-21A altimeter-
The unit computes corrected pressure altitude
encoders. The signal is based on the standard
from the inputs of indicated static pressure,
atmospheric pressure of 29.92 inches of mercury.
total pressure, and information on the aircraft
static-pressure error. All of this information
Air Data Requirements
in the computer is on a two-dimensional cam. The
cam is readily replaceable if it should fail or if
The basic functions of the air data computer
you must calibrate the unit for another type of
in the Air Traffic Control Radar Beacon System
aircraft.
(ATCRBS) are to correct the sensed static pressure
and the provision of appropriate outputs of
operation. A small step change in static pressure
altitude. The altitude outputs are usable in two
causes the aneroid capsule to deflect, rotating the
forms--a digital output in 100-foot increments
rocking shaft assembly. The rotation makes the
for wire transmission to transponders, and
Geneva sector and locking disk rotate the
an analog synchro output for providing pressure
microsyn rotor from its null position. Alternately,
altitude information to an AAU-19/A servoed
a correction for static-pressure defect can rotate
altimeter. The system also includes a failure
the microsyn rotor. In either case, the error
monitoring circuit. Table 6-2 gives the general
voltage generated is amplified and directed to the
computer requirements for the CPU-46/A and the
two-phase servomotor. The servomotor drives the
CPU-66/A.
Table 6-2.-Computer Requirements
6-20