RobertL18C wrote:
Annex 2 (now 1?) without a built in electrical system do not need to have the Txp always on when airborne, precisely to conserve battery for essential COMs and when either on a radar service or in a TMZ.
Where is that stated? SERA says:
SERA.13001(c) Except for flight in airspace designated by the competent authority for mandatory operation of transponder, aircraft without sufficient electrical power supply are exempted from the requirement to operate the transponder at all times.
which makes sense, but I can’t find any specific reference to Annex 1.
Robin_253 wrote:
Most transponder equipped gliders carry two 7Ah batteries though.
At the club where I fly gliders, the basic trainers have a single 7 Ah battery. This powers the COM, TXP and Flarm throughout the full gliding day, which is maybe about eight hours. Competition gliders have two batteries, but I think the main reason is that they also need to power the flight computer (think of a GPS with some additional, gliding-specific features such as polar diagrams and final glide compute).
For what it is worth, when I had an en-route generator failure two years ago, I first had a call from ATC complaining he had lost my mode C. I had not noticed the generator failure. Then the (old analog) autopilot started misbehaving. Only then did I take note and saw the tiny red low voltage lamp glowing in the sunlight.
Why mode C output should be lost from reducing voltage from around 13½V to around 12V I do not know, and it should not do that according to specs, but mode C was up again as soon as the generator was back on the bus. With a fairly contemporary GTX 330 mode S transponder.
