A question from a chopper driver

[Geoffersincornwall]

I know little about the modern fixed wing airliners but would like to know a little about the way the aircraft systems are managed in the event of a total electrical failure...

a, Do you have a way of managing the engines manually?
b. I guess with a FBW aircraft there is no way to control the aircraft if you have no electrical power but do you have enough battery power on something like a A380 to run an essential bus with enough systems to get you down? The quadruple engine failure of the BA 747 (volcanic ash) all those years ago must have deprived the are of all the generator power so I guess they must have had enough battery power to try the restart.

Would appreciate some general info if someone could oblige I would be grateful.

G.

[Tourist]

30mins from battery is I think the minimum for airliners.
Remember that most have an APU which will give electricity also, plus often a RAT which pops out. lots of options.

Certainly an Airbus absolutely needs electrics to be operated.

[Uplinker]

Hi. A320/321 can fly for 17 mins on batteries alone; 22 mins if you pull certain circuit breakers, or was it 22/29 mins? (Can't remember how long the A330 can fly for on just batteries.)

They have a ram air turbine (RAT) which will deploy if AC bus 1 and 2 fail. This pressurises the Blue hydraulics, which can run an emergency generator. (I can't remember the A330 specifics, but it is similar.)

Each engine has a small alternator which powers its FADEC above something like 12% N2, so in theory, the engines - once running - can run with no external electrical power? I am not 100% sure about this and am just back after an "oh god o'clock" early today, so I have no energy to look all this up now.

[Geoffersincornwall]

Many thanks for the info. One other point, do you need to pump fuel to the engines or to manage fuel distribution?

G.

[Uplinker]

The engines have mechanical low and high pressure fuel pumps, and they can be gravity fed (with some altitude restrictions) from the wing tanks if the (electric) tank pumps are not working.

Some fuel - about 2 tonnes - from the centre tank is unuseable without the electric pumps.

.

[FlightDetent]

A320: gravity fuel feeding procedure (https://ctrlv.cz/shots/2016/05/01/3TM7.png).

[Geoffersincornwall]

..... and manual engine control? Are the throttles FBW too?

G.

[FE Hoppy]

Fadec are generally powered by their own engine via a separate little gen (PMG) so loss of main busbar doesn't equate to loss of engine control. Same with FBW. There may be a back up battery(Ejets) or It may also have separate gen (CS).

Plus if you have a RAT the chances of loosing essential power are almost zero.

[Geoffersincornwall]

Thanks Hoppy

G.

[Piltdown Man]

Each aircraft has its own specific set of fail-safe systems. The Fokker 70/100 for example did not need electrical power to fly. From memory it was also pretty easy. As you were physically connected to the engines, electrical power was not required to control them. A backup display was powered by small dedicated generator each engine. All you really lost were a few displays and tea on demand.

More recently designed FBW aircraft, as stated above, have their own redundancy modes built in. The Embraer 170/195 series has three generators (engines plus APU), two batteries that will last for just 10 minutes :eek: and a RAT. In addition to that there is a dedicated battery to power (some of) the aircraft's flight controls for 15 minutes.

The way it works is as follows: Given a sudden dual generator (or engine) failure the RAT will automatically deploy. This coupled with the batteries will mean (allegedly) that the aircraft will remain totally flyable throughout the failure. The batteries will then be used to start the APU once its starting envelope has been entered. Throughout the emergency various system will be automatically shed and even when the APU comes on line not every system will be reinstated. But you will have more a flyable aircraft. This aircraft's engines, like the ones described above, have FADEC and each is powered by its own dedicated generator. Once you have everything under control you land as soon as practicable and change your underpants.

PM

[Geoffersincornwall]

Piltdown - useful stuff, thanks.

G

[Uplinker]

As well as conventional electrical fuel pumps, the BAe 146 has a couple of hydraulically driven fuel pumps, which can obviously function without electrical power.

[ZeBedie]

On later Airbus's, even the standby ASI & ALT require battery power, so they must have convinced the regulators that flight on battery will never happen.

[ukv1145]

Throttles on all FADEC aircraft are FBW (not to be confused with some EEC controlled A/C that have mechanical backup but are not considered full FADEC) - simply resolvers providing a Throttle Lever Angle (TLA) - same on rotary wing machines such as the S92.

[Uplinker]

My car's accelerater pedal is FBW!

Well, drive by wire I suppose.

[XV666]

So is my motorbike throttle.

Twitchy bugger, too, until you get used to it!

[Uplinker]

Yeah, ask Guy Martin about that! Although I think it was a traction control system that threw him off?

[FE Hoppy]

FADEC and EEC are completely interchangeable terms depending on the engine manufacturer.

The FADEC (single channel) controlled engines on the RJ have the "resolvers" on the engine with a mechanical linkage from the levers.

The EEC (which is the control part of the FADEC) on the PG1500 are resolved at the thrust levers.

There isn't even a standard definition of FADEC
Full Authority Digital Electronic Control on one engine and Full Authority Digital Engine Control on another.

Best not to speak in absolutes.

[tdracer]

This is pretty standard design for Boeing - the FADEC is powered by a dedicated gearbox mounted Alternator or Generator (PMA/PMG), and the throttle resolvers are powered by the FADEC/EEC (the 'official' Boeing term is EEC but yes, the terms are used interchangeably). The PMA/PMG will keep the FADEC powered down to less than 8% N2 (or N3). The engines will run just fine with no input from the aircraft aside from the (FADEC powered) throttle resolver (assuming of course fuel is available - and the engine driven pumps can provide 'suction feed' of the fuel).