Quoting Mikey711MN (Reply 85): From an aviator's perspective, by the time the transponder is shut off in case of fire, what would be left on? To a layman, I would think the transponder is, in fact, continually necessary in flight.
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Having the transponder on is not necessary in itself. It is just nice for the ATC guys down there.
In practice, you need the transponder in order to be visible for ATC. Certain (functional) equipment is prescribed by aviation laws, and so it goes. But if you have a good reason (like suspecting electrical malfunction, a fire... etc.), just turn it off. But it's polite (as well as necessary) to inform ATC then.
Of course there may are circumstances where you do not inform ATC, for example if you are busy fighting to stay alive in a damaged airplane.
You can switch off quite many things - for example flight computers, air conditioning, IFE, fuel pumps, ignition, the transponders, the CVR, the FDR... An engineer or a pilot can give you a much better answer. But the fact is that you can lose very much and still have a safely flying plane.
Quoting Mikey711MN (Reply 85): Conversely, in case of massive electrical failure, what systems remain on, i.e. running on some other power source? Would the transponder kick off then? If so, are other avionics still available? |
There are standby instruments (airspeed, compass, altimeter) that are independent of any electricity. You can run VHF and
HF communication off batteries, for example.
I don't know if I understand you right, but transponders are either on or off, but they do not "kick off" in an emergency like the ELT does.
AFAIK there are the following redundandy levels:
- each engine has an electrical generator, each of which suffices for powering the aircraft. But I don't know if the 777 engines can produce electricity by windmilling.
- the batteries mainly give you power for communications.
- if the engines quit, there is the RAT (ram air turbine), that is nothing else than a wind power unit. It suffices to power hydraulics and basic instruments.
- if the RAT quits... well.
But for more precise answers, you could can google for "777 Electrical", there is a very thorough document out there on smartcockpit.com (but I don't have the time and the interest to read it myself, though).
David