Operator Q&A: When Your APS-80 Autopilot Won’t Engage
Every day, I received phone calls and emails from operators with questions about their avionics units or systems. Keep reading to find the answers to a recent question.
I am having a problem with my APS-80 autopilot. It is disengaging during change of attitude i.e. during climbing or descent. We have checked the APC and it is okay. What else should we check?
There are several possibilities causing this failure.
1) The APA-80 has torque limiting monitor circuitry that can cause a disconnect if it is starting to get out of tolerance. This will typically fail when a significant pitch change is initiated. You can isolate this by swapping out or substituting another APA.
2) There are also two accelerometers NAC-80 that both feed the APA for hard over monitoring. If one of them gets out of tolerance to where it outputs a signal indicating a “hard over” condition and the other one is not, that will also disconnect the autopilot.
One thing to look for is if the #1 NAC is also feeding the pilot’s Flight Director Computer for signal conditioning of the vertical signal in altitude hold mode. This will sometimes show up as erratic Vbar jitter or pitch command when in alt hold mode.
Likewise, if the system has dual Flight Directors installed, the # 2 NAC-80 feeds the co-pilot’s Flight Director for the same purpose.
Aircraft is out of trim at AP disengage, so that means it is a trim problem, not a indication problem.
from “OldAutopilots” cd
In aircraft types that do not provide a horizontal trim rate feedback signal, the APC trim
command + output voltages are fed back into the APC trim rate input ports, and the trim system
is assumed to move when commanded. If the pitch trim system does not move when commanded, the problem will soon be apparent to the crew, because a continuous mistrim
annunciation will result.
The APC-80 contains trim monitoring circuits to determine that the trim circuits and trim system
is responding correctly. The monitors detect opposed trim, inoperative trim, or trim motion in the
wrong direction. The trim monitor provides two trim fail outputs, A and B. Each controls an
external relay, either of which removes power to the trim circuits in the APC and illuminates a
trim fail annunciator. Trim failure annunciations are latching and require correcting the problem
SEA Avionics Rad Alt, this may be for a RT-300
MKV EGPWS Interface Control Document
ALT 55 Radio Altimeter
Single or dual ALT 55 analog altimeter interfaces are supported. The signal format is as follows.
Scale: For Radio Altitude <= 500 feet:
Volts DC = (0.02 × Feet) + 0.4
Scale: For Radio Altitude > 500 feet:
Volts DC = 0.003(Feet – 500) + 10.4
Range: -20 to 2500 feet AGL
Valid range is > -12 feet AGL. If adjustable, the on ground voltage should be set to between +0.2 and +0.3 VDC.