blueflyer
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Isolating Cabin Power From Systems Power

Fri Jul 15, 2011 5:48 am

I'm just wondering with more and more airlines providing in-seat power outlets, what do they use to prevent a fault in cabin power from affecting the rest of the aircraft.

I'm sure *something* is in place, but I'd like to know how it's done.

[Edited 2011-07-14 22:48:32]
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David L
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RE: Isolating Cabin Power From Systems Power

Fri Jul 15, 2011 8:56 am

The brief, non-expert answer to your question is that there are several separate circuits, each of which can be deactivated independently. It's like the wiring in a house. You have, for example, a fuse or circuit breaker for the ground floor lights, another for the upstairs lights, another for the kitchen outlets, etc. Removing a fuse or tripping a circuit breaker will only deactivate that circuit.

The Swissair 111 accident immediately springs to my mind. In that case there was frequent reference to the "essential bus". The idea being that only systems essential to flying the aircraft were to be connected to it so that all non-essential systems could be deactivated if necessary. From memory, on SR111 the IFE system had been connected to the essential bus (I can't remember the reason) so, when it started causing electrical problems and subsequent fire, it couldn't be isolated without losing essential flight systems. I don't think the crew even knew the IFE was running on the essential bus so they didn't realise that they hadn't eliminated it as the source of the problem by isolating each of the non-essential circuits.
 
DashTrash
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RE: Isolating Cabin Power From Systems Power

Fri Jul 15, 2011 12:39 pm

I don't know about other bizjets, but in the Citation X we have a guarded switch in which we can shut off all power back there except the emer lights. On the Dash 8 you'd be pulling breakers or going down to essential power (more likely).
 
Goldenshield
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RE: Isolating Cabin Power From Systems Power

Fri Jul 15, 2011 1:52 pm

A plane has several busses on it. Each of those has different purposes in relating the operation of the aircraft.

Thus you'd expect something like this:

A couple main busses,which take power straight from the generators. The most critical thing these busses feed is the the essential bus,which ensures that power is provided to the essential items at all times, as they are required to maintain safe flight.

Also going off the main busses, are utility busses, which power everything else required to operate the aircraft, and finally, a service bus, which would power things like the galley and passenger items.

Should a generator drop offline, there will still be power to the essential bus, as the main bus (if automatic, or the pilots, if manual) will shed the other busses in order of least importance that it has to in order to feed the essential bus.
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Mir
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RE: Isolating Cabin Power From Systems Power

Fri Jul 15, 2011 3:17 pm

Quoting DashTrash (Reply 2):
I don't know about other bizjets, but in the Citation X we have a guarded switch in which we can shut off all power back there except the emer lights.

The CJ series has the same thing. On the Challenger 300, it's a pair of pushbuttons, one for DC and one for AC - push them and the cabin power gets shut off. Cabin power will get shut off automatically (load shedding) in the event that you go down to a single generator (out of the three on the airplane - two engines and an APU).

-Mir
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