Autopilot KAP150 Strangeness

[Bennett]

For about a month and a half I have had a slight (no change in altitude, just a small rotation about the CG) bobbing in pitch.  Not a big deal, but annoying.  I flew my M20J to LAC Avionics at San Jose Airport, as I had them work on my prior Mooney's autopilot (a KFC 200).  They immediately found a problem with the AI - an imminent failure, and I agreed that a rebuilt AI was necessary. They had a rebuilt AI shipped up (Mid-Continent) and they calibrated it for the KAP150.  In another thread I described the problem of turning the aircraft while the AI was spinning down in certain limited situations, and the subsequent second replacement of the AI, and re-calibration.  The new AI is rock steady, but the slight bobbing continued.  The good folks at LAC Avionics suggested that we send the KAP150 and the pitch servo to Honeywell for further testing. Yesterday I received a call to the effect that the KAP150 was failing its specification tests, and that this was due to a Lake amphibian logic chip in lieu of the Mooney chip, and that the software version is for the Lake. They checked the serial number of the KAP150, and it was factory installed by Mooney.  No one seems to have any idea of why the Lake chip (and Lake specific software) is there. Fortunately the chip is in a socket, or so they say, so switching chips, and the loading of Mooney software will be accomplished at Honeywell. They have not yet run all the tests for the pitch servo, but I am hoping that when we get the KAP150 and pitch servo back to LAC Avionics, all will be well once LAC once again calibrates the AI output to KAP150 with the now correct software/chip version.  All of this, of course, is getting expensive, but one day the bobbing will be gone (hopefully). I still don't understand how the Lake software and chip got there, but certainly Lakes, with their pusher prop on a pylon behind the cabin must have different flying characteristics than a Mooney.  I'm amazed that the KAP150 did so well over the past couple of years i've owned this Mooney. It will be interesting to see what it will do once everything is corrected and calibrated.  

[Marauder]

Bennett, strange things happen in avionics shops. I suspect if you are not the first owner since th AP was installed (and even if you are), it may have been swapped out during troubleshooting of a problem. Sometimes these guys swapped a known good module or EPROMS during the course of troubleshooting only not to reverse things afterwards. In my field of endeavors, we call them "no good board swappers".

[carusoam]

Bennet,

What year is your J? (My KAP150 was installed in '94)

Best regards,

-a-

[Bennett]

Carusoam, 1983 model, I would have to look up the date of manufacture.

[flyboy0681]

I noticed the same behavior in March while on a long trip. I wasn't sure if it was my imagination or just the currents at altitude but I sensed a constant up/down motion while the KAP 150 was engaged. On the return portion of that flight I still noticed it but coincidentally or not, I lost the vacuum pump on the last leg (right over lake Okeechobee) and watched the AI roll over and play dead. Since the pump was replaced I haven't sensed the motion any longer.

[Bennett]

It wouldn't surprise me that replacing the vacuum pump would have solved your "bobbing" as the AI provides an amplitude modulated signal to the KAP 150, and if the AI is slowed by low vacuum, this signal will probably be erratic, or at least less than optimal. Glad your problem was solved comparatively easily

[Awqward]

Since I'm new to the KAP150 maybe someone can advise me on GS intercept behavior.... The system behaves exactly as described in the manual when intercepting the front course ILS.... I set HDG and ALT when being vectored and when on the intercept course I press APR...the APR light flashes and as it turns in and captures the localizer stops blinking and remains on...so far so good....now I'm waiting for the glide slope intercept....the APR light is on as is the ALT light.... I would now expect the GS light to come on when the glide slope indicator is at zero deviation.... HOWEVER, I often have wait until one or two dots fly-down indications before It switches to GS mode...thereafter it recaptures the glide slope and behaves as expected.....is this normal?

[DonMuncy]

My KAP 150 intercepts the glideslope immediately, the same as with the localizer.

[Awqward]

Thanks Don....the fly through the glide slope problem doesn't always happen...sometimes it captures and sometimes it goes through and then captures....so it sounds like this is NOT normal....

[PTK]

Anthony, on my KFC150 the GS mode arms after the localizer course has been captured. It will then proceed and capture the GS (gs annunciator light on computer on) as the aircraft comes into it from either above or below.

If I'm outside the gs intercept and on proper altitude, even though the gs is armed and has not captured yet, I still see the pointers start to come down in the HSI. This seems the gs is captured but it's not yet! Not until I'm sufficiently close to intercept.

It sounds to me that yours may be functioning ok. Could it be that when it seems it hasn't captured the GS after having flown through it, the airplane is still outside the intercept?

These are some of the parameters the computer looks at that must be satisfied for gs intercept.

[Cruiser]

not sure if this helps but as I understand the KAP150 requires a minimum time to establish G/S after the APR has been selected and is flashing. I believe it is 45 seconds. 

In other words, if you turn onto the localizer too close to the FAF and the APR mode is activated there may not be enough time for the G/S to activate and take control of ALT.

If the plane flies through the G/S intercept, and is above the altitude the autopilot will not capture G/S. It must capture the G/S signal before the intercept and fly into it from below, the autopilot will not dive from above the G/S to capture it.

[flyboy0681]

not sure if this helps but as I understand the KAP150 requires a minimum time to establish G/S after the APR has been selected and is flashing. I believe it is 45 seconds. 

In other words, if you turn onto the localizer too close to the FAF and the APR mode is activated there may not be enough time for the G/S to activate and take control of ALT.

If the plane flies through the G/S intercept, and is above the altitude the autopilot will not capture G/S. It must capture the G/S signal before the intercept and fly into it from below, the autopilot will not dive from above the G/S to capture it.

 

 

You are correct on all accounts. This happened to me just last week. I pressed APR as I was passing through the FAF and the G/S didn't take.

[RJBrown]

The auto pilot in N1079V exhibited a porpoising action when I first bought it. Seem the previous owner never used the auto pilot. Two shops could not duplicate nor repair. All their cleaning, lubing and adjusting had no affect. Problem went away with further use.

[Awqward]

My KAP150 starting to porpoise last night in smooth air 8000ft.....3hours into the flight....not sure where to start looking for the problem....I did notice the AI was at an awkward angle before startup but it erected ok....

[Awqward]

I haven't been able to replicate the porpoising since...any ideas on what may have caused it?

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[Awful_Charlie]

Intermittent faults are always a sod to nail down. If you can at least make the problem reproducible, you stand a better chance of getting to it, but I would be tempted to get the AI checked out after doing the 'full and free' on the trim and elevator movements.

 

I have an intermittent problem too, which I've not had enough occurrences of to work out any pattern - sometimes after LOC intercept in APPR mode the AP commands a climb to the glideslope, which has raised a few eyebrows when it occurs. I't happened at two different airports a total of three times now, and am thinking maybe a short loss in the GS signal received might be the culprit

[Awqward]

Yes, I've had the climb response once or twice....although not for many months....I guess you always need to be ready to disconnect and hand fly any approach! ;-) Just yesterday it all worked flawlessly into Aberdeen Sent from my iPad using Tapatalk