Basically the SUPRA light just comes on if it receives a reply that is
above a certain very high power level (it then assumes it MUST be from your
aircraft). A more common problem is for it to *miss* it (i.e. doesn't
quite trigger the SUPRA sometimes) and it thinks that your own response is
rather an aircraft VERY CLOSE BY. Lights all the range lights and starts
shouting at you.

Sitting on the ground the other day (engine off, avionics off, just sitting in
front of hangar watching planes), I noticed that the SUPR LED comes on even
with only one bar on the range gauge lit. Not sure I know what the SURP light
means any more when it's not announcing my xponder reply. Thought it meant
traffic was being rejected outside the 2500' cylinder, but clearly, something
else is going on here.

Mike Palmer
Excellence in Ergonomics