Paul, interesting was an FAA test of 548 transponders at Sun-n-Fun and
Oshkosh '97 (voluntary basis; not representative of ATC users).
Altitude errors 3%, using tight ATC tolerance, but only one way off.
Strongest "passing" correlation was whether radar services regularly
used by owner, but biennial checks no correlation. Much more
significant was # of boxes off spec in general, so as not to be seen
by ATC or TCAS at all.
The "cycling" thing is curious. We don't recycle comm or nav to fix
them, and nothing in xponder/encoder circuitry is peculiar in that
regard. It may have to do with older ATC hardware/software. They get
Mode C only every third radar sweep, and beyond the pressure alt
correction, there's much deduction in software before it decides its
valid enough for display to the controller.
Best,
Fred F.
> Hi all,
>
> Generally most of my cross country flying is IFR, (too lazy to navigate I
> guess) and I find when listening to the general chatter on ATC that
> mis-reporting of transponders is a common dialogue I hear. The issue is
> often resolved by the aircraft concerned cycling their transponder.
>
> Obviously this is not the greatest situation, if you didn't have ATC telling
> you that something is amiss then you would have no way of knowing.
>
> Cheers, Paul
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