All electrical vs all engine failure B747, A320

[sebul]

Hi gang. Any idea on what the differences would be on the cockpit regarding an all electrical vs an all engine failure? I would imagine that the indications would be the same except with the electricals, that the engines would still be operating.

Thanks!

[A-FLOOR]

When you say "all electrical" do you mean including the ESS buses?

In any case, I think I'd rather have an all electrical failure... you will still have control of the aircraft as long as the engines are running and hydraulics are pressurized. Interestingly an all-engine failure in the 747 would mean you have to descend to an altitude that permits the APU to be started since the 747-400 does not have a RAT. Not having engine power would of course mean you'd be resigned to doing that, but it does limit your options as I believe there is nothing to power the pneumatic and electrical backup pumps when the engines are not running until you can get the APU online... then again I'm not sure if the 747 has static inverters to generate AC from the DC batteries.
The A320 does have a RAT to generate electrical power and hydraulic pressure in case of a dual engine failure, and contrary to popular belief the A320 does not plummet to earth when all electrics are out: the lowest flight control mode (mechanical law) does not require any electronics but permits control of the aicraft through the elevator trim and rudder.

[vapilot2004]

More lights and bells with an all engine failure. The seat cushion would probably look different too.

[Intruder]

Interestingly an all-engine failure in the 747 would mean you have to descend to an altitude that permits the APU to be started since the 747-400 does not have a RAT.

Nope. The APU can't be started while airborne (prohibited in the Classic, and I believe inhibited as well in the -400).

Emergency electrical power (batteries) can be used to restart the engines; there are inverters to provide essential AC power. Hydraulic power is sufficient with windmilling engines down to 160 KIAS.

[sebul]

Originally Posted by A-FLOOR

When you say "all electrical" do you mean including the ESS buses?
\

My question was with regards to all the normal AC power sources being offline with emergency backup power still available.

With the 747-400, I believe that you can't start the APU in flight, so there really is no use for the descent. I've seen an all engine failure in a 747 sim and only the Capt's PFD, ND and the primary EICAS worked while the emergency lights automatically turned on. Still had control of the aircraft though, through the standby bus (I am prepared to be corrected on this). And 747s do have inverters for DC to AC and vice versa.

Originally Posted by vapilot2004

More lights and bells with an all engine failure. The seat cushion would probably look different too.

...and feel different too.

[Short_Circuit]

Well now you know about the ALL ELECTRICAL scenario ie QF2

[18-Wheeler]

Nope. The APU can't be started while airborne (prohibited in the Classic,

Some classics you can - Depends on the way they're wired-up though.
You have to have a bit of luck going for you as well as the inlet door isn't designed to for in-flight starting.

[GlueBall]

sebul:"...an all-engine failure in the 747 would mean you have to descend to an altitude that permits the APU to be started..."

...To be sure, you'd definitely be descending irrespective of whether you needed/wanted to or not!

[Phil Squares]

On the 400, the APU is certified for inflight operation. There is no ability to start the APU inflight.