KAP 100 Autopilot
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KAP 100 Autopilot
I occasionally get to fly an aircraft fitted with a KAP 100 Autopilot.
I've never bothered to use it, but I'm curious as to why it has an amber TRIM light. I was under the impression that this was a single axis autopilot and had no control over the pitch trim?
I've never bothered to use it, but I'm curious as to why it has an amber TRIM light. I was under the impression that this was a single axis autopilot and had no control over the pitch trim?
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Maybe this helps: http://www.flymafc.com/docs/king-autopilot100.pdf
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I have no idea if this applies to the particular installation in this case, but there is an important safety issue with all autopilots that are able to drive the elevator trim.
If something goes wrong with the direct pitch control (either because the pilot or passenger is pushing/pulling the yoke, or because the autopilot servo (or some other subsystem) driving the pitch axis, has failed) then the problem can be masked by the autopilot's elevator trim action.
Then, some seconds or minutes later, when whatever was messing with the pitch is no longer messing with it (the human input has ceased, or a circuit breaker has tripped on the defective pitch axis) the aircraft is suddenly massively out of pitch trim.
At cruise speed, it's very possible for the required yoke correction to be more than a human pilot can manage. It's even possible at takeoff speeds, in some types, if the elevator trim is wound all the way back prior to rotation.
This is why autopilots are supposed to have additional features to prevent a trim runaway condition. As one example, my KFC225 will disconnect if the pitch trim has been running for more than about 15 seconds. In reality this detection is normally done in software, and American avionics software..............is going to be hardly foolproof, especially at the GA level of quality where an autopilot failure is deemed to be acceptable at any time.
Autopilots are the most wonderful things for reducing cockpit workload and thus promoting safety, but it's important that a pilot flying a plane with an autopilot understands fully how the autopilot is supposed to work.
If something goes wrong with the direct pitch control (either because the pilot or passenger is pushing/pulling the yoke, or because the autopilot servo (or some other subsystem) driving the pitch axis, has failed) then the problem can be masked by the autopilot's elevator trim action.
Then, some seconds or minutes later, when whatever was messing with the pitch is no longer messing with it (the human input has ceased, or a circuit breaker has tripped on the defective pitch axis) the aircraft is suddenly massively out of pitch trim.
At cruise speed, it's very possible for the required yoke correction to be more than a human pilot can manage. It's even possible at takeoff speeds, in some types, if the elevator trim is wound all the way back prior to rotation.
This is why autopilots are supposed to have additional features to prevent a trim runaway condition. As one example, my KFC225 will disconnect if the pitch trim has been running for more than about 15 seconds. In reality this detection is normally done in software, and American avionics software..............is going to be hardly foolproof, especially at the GA level of quality where an autopilot failure is deemed to be acceptable at any time.
Autopilots are the most wonderful things for reducing cockpit workload and thus promoting safety, but it's important that a pilot flying a plane with an autopilot understands fully how the autopilot is supposed to work.
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it's important that a pilot flying a plane with an autopilot understands fully how the autopilot is supposed to work.
The aircraft in question has electric trim which is not commanded by the autopilot. But I guess that doesn't stop a malfunction from occuring.
Apart from having a split trim switch and C/B's, are there any other measures taken to prevent the trim from "running away"??
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If the trim is just manual+electric then it won't run away unless there is a wiring or similar defect.
In a system where the AP does not do pitch trim, the likelihood of a trim fault depends to a large degree on whether the trim is part of the autopilot. On my KFC225 it is permanently so, so e.g. a firmware fault in the AP (which has no hardware watchdog) could cause a trim runaway. However most other electric trims I have seen were completely separate from the AP; they were just a switch on the yoke connected to the trim motor.
If the trim did run away for some reason, the autopilot would try to compensate using the elevator, until something trips out, and then you suddenly get a massively out of trim aircraft.
Checking the trim position on the pre-takeoff check is very important. To get this wrong is likely to be deadly.
In a system where the AP does not do pitch trim, the likelihood of a trim fault depends to a large degree on whether the trim is part of the autopilot. On my KFC225 it is permanently so, so e.g. a firmware fault in the AP (which has no hardware watchdog) could cause a trim runaway. However most other electric trims I have seen were completely separate from the AP; they were just a switch on the yoke connected to the trim motor.
If the trim did run away for some reason, the autopilot would try to compensate using the elevator, until something trips out, and then you suddenly get a massively out of trim aircraft.
Checking the trim position on the pre-takeoff check is very important. To get this wrong is likely to be deadly.
