View Full Version : FBW hyd failure

17th Mar 2003, 21:00
Hiya, I have been looking for a schematic but can't find one so I will go from the top of my head...
What happens if their is a complete engine failure on a FBW aircraft such as the 777 or A3x0? You lose the engine driven hydraulic pumps and the main buses therefore the electrical driven pumps also as caused by the engine failure, say due to fuel starvation. What happens if the RAT fails to extend? You are left without any hydraulics and their is no manual reversion. What do you do??? Aysemtric (SP?) thrust is out of the question (no engines!) so how do you stear the thing? Also do you lose the EFIS displays?

17th Mar 2003, 21:46
Hi rich,

the short answer to your conundrum for the A320 is: you need hydraulic pressure to fly the aircraft. Period.
I see two possibilities in the case you postulate:

1. get the RAT to extend by pushing the electrical or hydraulic panel manual extension buttons

2. start the APU (provided the aircraft is within the start envelope, otherwise you would waste valuable battery power, but in my opinion, you would try anyway....)

The screens going blank on battery power alone are the least of your worries in that case (one is left with Capt PFD and ND on battery).

Cheers Rapide

19th Mar 2003, 00:58
Rich. With reference to the Airbus, unless all the engines seize (unlikely), then the continued rotation of the engine, and thus the Engine Driven Hydraulic Pumps, will provide enough hydraulic pressure to power the flight controls. If the emergency generator, should also fail then the batteries will still provide the required ergs to keep Prim 1 and Sec 1 (Flight Control Computers, A330/340) going and therefore a degraded regime Flight Control Law (Alernate Law).

30th Mar 2003, 19:01
As above at 160 knots you should have a core engine speed above 10% and this will be enough to provide the hydraulic energy you need (not one volt of electrical power though - so your best bet is to start the APU).

Don't rely on the RAT in isolation it makes a hell of a lot of noise but won't give you as much hydraulic fluid flow as you need when you slow down (especially if its turbulent)

30th Mar 2003, 19:30
This question is a bit of the kind of if you lose both your arms and your legs, would you still be able to move?

Offcourse you need hydraulic power to be able to move your controls.

What AhhhVC813 says is very interesting... If both engines fail due to fuel starvation, the engines will windmill, and a N1 of about 12-20% is sufficient to power the hydraulics.

And without fuel... there is no APU.


31st Mar 2003, 00:21
Complete hydraulic failure, interesting topic.
SV very nearly had one some years ago when a wheel burst at altitude, rupturing hydraulic lines, leaving only one half of system D available on a TriStar. In this case, only the First Officer can land the aeroplane.
They were very lucky a small amount of fluid remained, so the F/O could do the job he was trained for...and well done too.