Question on C171 transponder control

[deansalman]

Hi there, have 2 questions

when I set the transponder to ALT it has a Fight Level. I am told that is suppose to be altitude above sea level. However, the readout is above the ground. So not sure which one to set on my Radio control for Saitek. I can set either one

Also does the C172 have a Idnet to use when ATC cannot read my squawk code. I can not find this guy

[LZ-WIL]

Hello,

I think the transponder altitude is in MSL, since it always shows the flight level I am currently at. My altimeter is set with the appropriate airport QNH before flight. The transponder may operate with standard pressure every time on the other hand - not quite sure ). Real world pilots here and more experienced friends will let us know.

The "ident" function on Bendix-King KT-76C transponder model is done with a button marked "IDT" on the top left corner of the device just beneath the name.

Cheerz,
Will

[Nick - A2A]

The transponder may operate with standard pressure every time on the other hand [...]

Yes, just to add to Will's answer, flight level (which is what the transponder displays/transmits) is the altitude above MSL at standard pressure. This means the flight level shown on the transponder will only match the altitude you see on the altimeter if the air pressure is 1013.2 mb / 29.92 inHg (that's provided the altimeter is properly set). In the case mentioned above, it sounds like the air pressure was lower than this. For example, if the air pressure was 990 mb, this would result in the transponder reading FL007 at ground level.

Anyway, you should definitely set your Saitek transponder to match the flight level being shown by the Bendix King transponder in the VC.

Thanks,
Nick