KAP 140 autopilot and electric trim

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Piper_EEWL
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Re: KAP 140 autopilot and electric trim

Post by Piper_EEWL »

Nick M wrote:...This in one area where reality and FSX diverge somewhat: in the sim once the autopilot is engaged we can't overpower it at all and the only way to regain control of the aircraft is to disconnect it...
That's correct for the A2A fleet. But if I remember correctly in the PMDG MD-11 you can overpower the autopilot if you move your joystick when the plane is in AP mode. The MD-11 snaps out of AP mode if you just barely touch the joystick/controller. Or at least I remember it that way. It might be though that I'm mistaken her because it's been a while since I've flown the MD-11 in the sim (Not that I've ever flown on in RL unfortunately :wink:) So this could be implemented I guess.
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Re: KAP 140 autopilot and electric trim

Post by Oracle427 »

With a KAP140 the autopilot does not disconnect when you move the yoke.

It will resist you and it requires a decent amount of force to override it. This is very obvious in the roll axis, but may not be obvious in pitch due to the heavier aerodynamic forces on that axis.

What happens when you go against the KAP140 in pitch is that it will move the trim wheel to compensate and steadily increase the aerodynamic pressure against you. After a few seconds of continuous movement of the trim it will alarm and disconnect leaving you with a potentially dangerously out of trim aircraft. In this case the KAP140 treats itself as malfunctioning and can not be re-engaged unless you pull the breaker out to power down the unit and reinitialize it. I, uh, know a guy that learned this the hard way while his instructor watched and waited. :oops:

Edit: Fixed the fixes made by my silly phone spellchecker.
Last edited by Oracle427 on 28 Aug 2015, 12:56, edited 1 time in total.
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Piper_EEWL
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Re: KAP 140 autopilot and electric trim

Post by Piper_EEWL »

Oracle427 wrote:I, uh, know a guy that learned this the hard way while his instructor watched and waited. :oops:
Im sure that "guy" will not forget that experience. So maybe it was good that "he" learned the hard way :wink: :mrgreen:
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Nick - A2A
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Re: KAP 140 autopilot and electric trim

Post by Nick - A2A »

That's a good cautionary tale Oracle - thanks. Do you recall if you heard the “TRIM IN MOTION, TRIM IN MOTION...” voice warning at all? After reading the previously linked report more closely, I noticed that this feature of the KAP 140 was another direct result of the accident and subsequent safety recommendations: “An audio feature is also being tested. The audio feature will advise the pilot aurally if the elevator trim runs for more than 5 seconds during normal operation.”

With respect to the accident itself, I don't think it's clear whether it was having to overcome out of trim forces (from the aircraft being trimmed fully nose up by the autopilot) or having to actually overpower the autopilot pitch trim servo (if it was still engaged) which was the cause. Either way, it's a really good example of how a GA crash investigation can lead to both design changes and alterations to the checklist and hopefully prevent a reoccurrence.

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Oracle427
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Re: KAP 140 autopilot and electric trim

Post by Oracle427 »

Sorry about failing to respond to your question. No, I never heard a trim in motion alert, though it is possible that the KAP140 may have flashed something on its screen. Its mounted off to the right and down low, placing it well out of the normal scan area.

I know I have induced a runaway trim while on the ground while performing a run up with the AP engaged. It only alerted at the point when it disconnected.
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Nick - A2A
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Re: KAP 140 autopilot and electric trim

Post by Nick - A2A »

Thanks Oracle - I'd forgotten about it really: it was only the mention of runaway trim in the other thread that caused me to look up something in this one. :)

Nick

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AKar
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Re: KAP 140 autopilot and electric trim

Post by AKar »

The voice alerts would come with Honeywell SB No. KC140-M1, which in turn comes with Cessna SB02-22-01.

For several Cessna models which have this affected equipment installed, the software update is actually mandated by the AD 2004-15-18, albeit not because the voice messages but for prolonging the button hold time that comes with the same update. So if one's missing the voice message in any of the affected fleet, I'd really check the compliance with the AD.

-Esa

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Re: KAP 140 autopilot and electric trim

Post by Oracle427 »

Thanks Esa, I'll have a look. I have not attempted this on our new plane with a KAP140. This happened to me on a foggy school aircraft years ago. It seems like an easy one to verify on the ground as well as by reading the maintenance logs. As this is a 182, I certainly do not want to test this one in the air!
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Nick - A2A
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Re: KAP 140 autopilot and electric trim

Post by Nick - A2A »

Yeah, my understanding from the manual (p.89) was that the "trim in motion, trim in motion" and "check pitch trim" voice messaging was part of the 03/01 software update (which introduced the prolonged AP button press as Esa says), but that the other voice messages (for the altitude alerter and AP disconnect) were optional.

I think the other significant change that resulted from the same update was that only the AP button could be used to engage the autopilot, whereas previously it could be engaged by pressing one of the mode buttons. (e.g. pressing ALT would place it directly in altitude hold.)

Relating to the flight you described above Oracle, I gather the main annunciator panel in the 172/182 should show a "pitch trim" warning too. Of course, all pretty irrelevant for the purpose of the sim as none of this is simulated, even in the A2A version, but interesting to discuss with those who have access to the real thing and its paperwork! :)

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AKar
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Re: KAP 140 autopilot and electric trim

Post by AKar »

This AD is actually a bit interesting, for it mandates this software update for Cessnas, but does not apply for Pipers for instance, nor to the KAP 140 in general. The reasoning is the physical positioning of the autopilot unit in Cessnas, supposedly making it plausible accidentally, and while not noticing, to disable the AP.

This is actually a little bit "hazardous" AD, because it applies to the airplane, not equipment. This creates a risk when swapping units within a fleet of dissimilar airplanes, for example.

There is this condition:
  • (4) For all affected airplanes: install only KC 140 autopilot computer systems, part number (P/N) 065–00176–2501, P/N 065–00176–2602, P/N 065–00176–5001, P/N 065–00176–5101, P/N 65–00176–5201, P/N 065–00176–5402, or P/N 065–00176–7702, that have been modified as specified in paragraphs (e)(1), (e)(2), and (e)(3) of this AD.
Especially during the years right after the introduction of the AD, it is all possible that the documentation that is used does not take into account this restricted P/N range eligible for installation in case of a replacement for example, even if the Honeywell SB No. KC140-M1 did require you to modify the P/N sticker appropriately. Any other record, as in books or forms, of this performed update would in most cases only get logged into the airframe's book, as it is performed under instruction applying to the airframe. Under EASA, one even can not automatically certify the work done to the box specifically as per SB No. KC140-M1, for this would be component work, requiring its own licensing, thereby loosing the track of the box's status except for what is given by the sticker.

It is also possible that an airplane affected by the AD is in compliance with it, and therefore having the Honeywell SB No. KC140-M1 software embedded, but still not giving out the aurals due to some other issues. For instance, a failed buzzer. This would still be in compliance with the AD, but not necessarily with some other requirements that establish airworthiness.

Not very relevant to the simulation world, but that's just some stuff one routinely runs into in the airworthiness management business. :) Learning an airplane individual one has never seen before really opens quite many rabbit holes to check out.

-Esa

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