The Comair crash reminds me...

"Bob Moore" wrote in message
. 122...
Jim Macklin wrote
The slaved compass is corrected so as many errors
(deviation) are corrected and variation is also corrected as
much as possible too,

SAY WHAT!!!! How does one fly an ATC assigned heading if VAR
has been 'corrected' out?

Probably the same way you do it when there's a wind. ATC assigns you a
heading. If that doesn't provide the track they want, they assign a new
one, adjusting for the error in the track.

They don't care what your heading indicator is telling you. They care that
you follow it consistently.

(Note: I don't actually know anything about how a slaved compass is
corrected...seems to me that variation and local deviation (that is, not due
to the aircraft installation itself) are not things one could usefully build
into a slaved compass. But assuming the slaved compass IS correcting for
all manner of things, there's no reason to believe it would cause a problem
with ATC).

Pete