I've had situations where my mode C was malfunctiong and reporting an
altitude outside of the accepted range for IFR. In such cases, ATC
verified what altitude I was maintaining and asked me to turn the
altitude encoder.


"Steven P. McNicoll" wrote in message link.net...
"Magnus" wrote in message
...

I thought it was +/- 200 feet before you've violated if you are flying
IFR, but someone just told me it's a 100 feet, which seems a little
steep considering they use 1000 feet separations.


Depends what you mean by "violated". If your Mode C altitude is within 200
feet of your reported altitude you're considered to be on altitude.