Pitot/Static/Transponder Problem

Rich S. wrote:
"Dave" wrote in message
. net...
(snip)
Either the altimeter or encoder is off. Your allowed 125 foot deviation
between the two to be legal.
(snip)

Hmmm . . . interesting. Sometimes I fly over a local airport where the
controlled airspace tops out at 2,800'. Over that is Class B airspace with a
floor of 3,000'. So, I fly at 2,900' and figure I'm okay.

If my encoder is 125' different than the altimeter reading, I could be
reporting to either the tower or to ATC that I was infringing on their
airspace. Come to think of it, last time I flew over that tower (at 2,900'),
I requested a transponder check and they reported that I was showing 2,800'.
They didn't seem to get upset.

IIRC, the encoder reports in 100' increments, so I guess mine could be
anywhere from 49' to 149' off the altimeter. (it is VFR certified BTW).

Rich S.


Yep.
If you think about it if you fly at 2990' where class B airspace is at
3000', you could be squawking 3100 feet and be legal, sort of.
I don't know what altitude they can really bust you for, but you could
be totally legal and bust "B" airspace.

Does anybody have a read on what the ATC regulations are for this sort
of thing?

And one more tidbit, 91.217 says that the altimeter and encoder need to
be within 125' of each other, but no nothing to the accuracy of either
device. So if both your encoder and altimeter are off by 1000', they are
legal.



Dave
www.craigmileaviation.com
Dallas