Autopilot Altitude Hold - KAP-200

[lsearcy]

My autopilot is acting up and I was hoping for some troubleshooting from the brain-trust.  On a recent trip from Houston to 2L0, the autopilot was working well and holding altitude.  About 20 minutes into the flight the breaker popped.  I re-set it and it popped again.  I hand flew the remaining leg of the trip.  I thought there was an issue with a new PTT installed maybe arching near the trim switch.  I had that checked and no problem.

 

A few days later I flew to KLCH and AP worked fine including the altitude hold with a little bobbing up and down (maybe 50 feet in each direction).  Today, on an instrument currency ride the roll and pitch worked fine but the altitude hold would not work at all.  The annunciator showed that FD, NAV, and ALT were all coupled.  FD and NAV worked great but the Altitude hold would not lock in and hold altitude.  There was no auto trim working at all and when i tried to hand trim the plane it seemed as though the trim wheel was locked (trimming from the yoke worked fine but obviously cancelled the AP.)

 

Anyone else experience this problem?  Troubleshooting thoughts?

 

Thanks 

[carusoam]

What model do you have and how old is it?

Typical Mooney trim challenges come from old hardened grease sticking up the system.

This would be known to most Mooney mechanics...

Solution to this challenge is cleaning out the jack screwing the tail. And proper re-lubrication.

I am only a PP. Not a mechanic.

Best regards,

-a-

[KSMooniac]

Sounds like you need to visit a shop that is competent with autopilots.  It could be in the pitch or trim servos, or the computer.  Sorry I can't help with anything specific.  

 

I have a good KC-295 computer for sale with a good altitude board in case that turns out to be the problem.  I also have a pitch servo, but it needs repair.  I just sold a good trim servo.

[lsearcy]

Plane is a 1980 M20J.  Trim works great when autopilot is not engaged.  

[Piloto]

Try this first before spending any money.

 

1. Remove the A/P computer from its tray and spray contact cleaner on the contacts and reinstall.

2. Lubricate both yoke shaft with silicon lubricant. They have a tendency to bind in-flight if not lubricated.

3. On the tail lubricate the actuator springs.

 

I found the above to solve most of the autopilot intermitent problems.

 

Good Luck

 

José 

[jetdriven]

I'd be careful resetting th A/P circuit breaker. The servo might be going bad, or too much friction in the control system causing the servo to overload. On Century autopilots the servo overload blows the drive transistors in the console. At any rate, it could ruin more stuff. I have called Autopilots Central in Tulsa before about my autopilot, and they are experts. Many times they can pinpoint things on the phone.

[jlunseth]

To add to José's practical solutions, sometimes it helps just to cycle the trim switch at the start of the flight.  That will disconnect the AP of course, so you just set it up again it is only a few button pushes.  Also, it helps to feel under the trim wheel to make sure nothing has fallen down there that is intermittently jamming the wheel, and also to just put your hand on the wheel once in awhile to feel if it is moving when it should. The carpet in my aircraft is cut out under the wheel, which forms a perfect well for FOD to land and stay in. Sometimes it is something as simple as your safety belt being in the wrong place.  

[flyboy0681]

I have called Autopilots Central in Tulsa before about my autopilot, and they are experts. Many times they can pinpoint things on the phone.

 

I second the motion. They are more than willing to talk at length over the phone about an issue even if they don't get the business. They are experts on the King line of autopilots and turnaround repairs quickly. I also found them to be reasonable.

[AndyFromCB]

Call Randy at autopilot central. Or the crew at Capital Avionics. They do a great job on servo IRAN and overhaul at a lower price than Autopilot Central.

[Flynnupe]

Ive been having a similar problem with the Altitude hold in my 80 J with the KFC 200. My problem started occurring after I installed an Aspen two tube system. Im still trouble shooting, which includes several new EA-100 boxes, software updates etc. Let me know what Autopilot Central says, theyre my next stop..

[Awful_Charlie]

When the ALT hold is on, the clutch on the pitch trim servo should engage, so it will be nigh on impossible to move the trim wheel.  If however the trim system is stiff when the ALT/VS is not engaged, then that could well be the cause of your problems, although it  is more likely your trim servo is giving up.

 

You may also need to check the AI output to the AP input : rubbish in=rubbish out as they say

[cliffy]

There was an article many years ago showing that problems with 200 APs may be caused by bad grounding wires at the servos and all other boxes. You might just remove clean and re-tighten all the grounds and re-seat the computer and control head connectors.