GFC700 went offline

[lfreeman]

Yesterday as I was just about to intercept the localizer at KAUS the autopilot went offline and the red AFCS warning came up on the PFD. I clicked the AP disconnect switch several times but the AFCS warning would not clear and the AP would not come back online. I flew the rest of the approach by hand without a problem.
After landing and powering off and back on the warning was still there.
Anyone else ever have this problem? The plane goes into annual when I get back to Dallas so I will have it looked at then.e

[smoss]

One thing that has caused this for me is loss of a few GPS satellites for a bit. The AFCS system warning with AP disconnect, all other things looking normal, with no GPS warnings, but after hand flying for several minutes (in stormy bumpy conditions) and checking everything I could, I noticed several of the satellites on GPS2 were offline. 5 minutes later or so the satellites came back to life, and at that exact time the AFCS warning cleared and the AP worked normally again ever after. Never did I get a GPS warning, as still had enough for 3D nav, but appears there may be some minimum required for the AFCS.
Probably the luckiest cause for the warning!
Otherwise, probably a servo failure or something.

[Aart]

Assuming Layton was flying in heading mode and intercepting an ILS, his problem would not have been caused by the loss of satellites.

[smoss]

Aart, the AP will disconnect anytime there is an AFCS warning, my AP would not engage in any mode until the warning cleared. Not saying that is what his warning is from, just a thought.

[lfreeman]

I was in heading mode when it went offline. I will see if the problem reappears this afternoon.

[Tim M]

Did you still have the FD command bars?

[lfreeman]

Yes, the flight director was still working. Flew back today after the storms cleared for a while and had no issue with the AP.

[Tim M]

My understanding is that the autopilot is a "dumb" system that just follows the FD, where all the inputs and control laws reside. If that is true, then any loss of critical input should disable the FD.

[smoss]

Layton- sounds just like what happened to me. If it happens again pull up the GPS page (both 1 and 2) and check out the satellites.

[rwtucker]

Layton - I have had similar experiences in Northern Nevada and Southern Idaho. I later learned that classified "experiments that might affect GPS" were being conducted in Nevada during those times. One point of interest, flight services is either not told or is not permitted to confirm these tests. I called from the air on both occasions. They checked their briefings and could find no activity that would affect GPS. This past year, I started receiving FAA notices that GPS might be affected in certain areas according to distance and altitude from coordinates in Nevada. I did not receive notices the year before when I had the problems. A long shot, but you might check your area.