Section VII
Systems
VII-22-8
Flight Guidance Data Failures
When there is a failure detected in any sensor data used in the flight
guidance computations, the system internally reverts to the basic mode
for the affected axis, pitch attitude hold for vertical modes and roll
attitude hold for lateral modes. If the failure condition remains for a
period of time, typically four seconds, the flight director display
removes the steering command and annunciate the failure by placing a
red line through the active mode annunciation. The flight director
returns to normal operation if the data returns to a valid condition or
another operational mode is selected.
Response to flight guidance data is provided by pitch and roll attitude
and attitude rate limiters. These limiters limit the aircraft response to
those approaching normal maneuvering; 5 °/second of roll rate in the
lateral axis, and 0.2g in the vertical axis.
Aircraft response to failures which result in main processor servo
commands exceeding the maximum rate limit are limited by the I/O
processor cutout function and servo torque limiting. If the aircraft
exceeds predetermined attitudes, attitude rates, or accelerations, the
I/O processor will zero the command going to the servo control loop.
The servo drives the control surface toward the position it was in prior
to the malfunction. The cutout switch is activated only if the command
is in the opposite direction to arrest the malfunction.
In addition to the cutout function, servo torque is limited through direct
electronic limiting of servo motor current. By limiting the maximum rate
of change of the control surface, torque limiting limits the aircraft
response prior to cutout operation.
10 Sep 2006