Experts, correct me where I'm wrong.

1. An operating transponder, not being interrogated, is simply a receiver
with a low current drain.
2. When interrogated by a ground radar or TCAS, a transponder transmits a
short "squitter" at 175 or 250 watts which is a BIG current drain.
3. Flying in an area with many interrogations per minute is likely to be a
congested area where the transponder is needed and a wise pilot would keep
it on despite the current draw.
4. Flying away from a congested area toward a remote area with few
interrogations, the transponder automatically cuts back on its current draw
by operating less and less as a transmitter and more as a receiver.

So, where is the need to turn it off? Doesn't the transponder effectively
manage its own current draw to match the level of congestion? Move away
from congested areas and the current draw is minimal. I haven't read of a
case where the transponder is sucking batteries flat and if that happened,
how much additional battery capacity is needed to keep it running for the
whole flight? (I can remember pilots carrying car starting batteries to run
a vacuum tube radio. No imaginable suite of avionics would draw that much
current today.)

So, aside from the cost of a transponder installation, what is the concern?

Bill Daniels

p.s. Having suffered a couple of alternator failures at night in hard IFR
with single engine airplanes, I became very interested in the current draw
of each bit of avionics. My calculations showed is that if the aircraft
battery is in good condition and fully charged at the point where the
alternator failed, and the pilot swiftly switches off the alternator field
with the split master, the battery will run a full IFR panel longer than the
fuel will last. I tested that calculation and it proved true with good
safety margins.