Cocomo wrote:

I realize you probably left this out on purpose to be brief, but technically
this is only true if GPS1 was already driving the autopilot or if GPS1 and
GPS2 have identical flight plans loaded and activated. It's not true if
GPS2 is flying the plane and GPS1 is inop or has a different flight plan
active. The Stec 55X will also still work in altitude hold or vertical
speed modes because its uses its own static pressure sensor separate from
the EFIS. These are the kinds of details autopilot users ought to know
cold.

Thanks for the reply.

Yes, that gets a bit too Cirrus-specific when answering to the general
autopilot question. But since you bring it up, I'm not sure what your
point is - the example referred to a PFD or ADAHARS failure resulting in
a loss of heading data sent to the 55X, which, if the 55X is currently
in HDG mode, will always result in the behavior I described. If the
autopilot is in GPSS mode, regardless of which GPS is providing the
steering input, loss of heading data will not affect that mode of operation.

-Ryan