If a 777 lost power to both engines, would the APU be capable of producing enough power to operate the flaps and other control surfaces ( at least minimally ) to aid the aircraft enough to land it safely?

Well, I guess you could use the APU to power flaps, via hydraulic (main) or electric (alternate) system, the landing gear could be lowered by gravity, and the control surfaces... maybe you could deploy the RAT or use the hydraulic power from the APU or both. Although, I'm not quite sure if there's some sort of overide that comes in if you have hydraulic power, then you cannot deploy the RAT. You can also run the trim if you have APU...I think you can manage to make a landing with those items functional.

(Oh, I hope I don't blow it like I did the last time with the freaking DC-9 trim)

If both your engines failed what fuel do you think would run the APU?

Unless you had another situation in mind that would result in total power loss...

Who said anything about engines failed due to lack of fuel?

And, yes...I know it is very unlikely that both engines fail for a different reason than lack of fuel

So you answered your own question...

According to Boeing, the RAT would be the first choice.

On most APU´s there is a max. altitude restriction for use. The two primary jobs for the APU is to provide electric and air. Through the electric it also provides hydraulic. The lower the altitude, the better the chance of the APU starting and supplying. There is no altitude restiction for the RAT (Ram Air Turbine) or ADG ( Air Driven Generator). They can provide hydraulic and / or electric. These emergency devices have a hard time providing several things at the same time so it is important to wisely select what you want the APU or RAT to do. If a RAT is used only the esential components are supplied. If all fails you have to rely on battery power, which doesn´t last much longer than 10- 20 minutes...depending on the load.

Lose both (all) engines on any big airplane and a SAFE landing is very much in doubt.

Yes that is very unlikely but if you were to fly through an ash cloud like speedbird 9 then it would happen. Here is what I am talking about: http://www.youtube.com/results?search_quer...m=0&spell=1


Yes I know there is a manual deployment switch on the overhead panel on the second column from the left, around the middle for the 777 overhead panel.


Yes that is right. The APU has a max altitude probably because of the air pressure at high altitudes.

Btw the airuser you are right regarding the trim on the 777, there is a system which works on pneumatic air as well as if you look at the pneumatics panel in the flt deck there are a couple of switches with "TRIM" below them..

Regards,
Chris

A question just popped in into my mind. How did the Air Transat A330 crew over the Atlantic to keep the cabin pressurized if there was no fuel to start the APU? Does the A330 (or any other airplane) have something that can keep the cabin pressurized? Or is it just because the pressurized air stays in the cabin no matter what? Oxygen masks deployed? They didn't make nor could have make an emergency descent...

Once the engines and packs stop supplying air due to switch off or shut down the cabin system trys to maintain cabin pressure by closing the air outflow valve. An aircraft however isn´t airtight and therefore the air will slowly seep out. I don´t know if the masks were deployed on the Transat or not...

The Air Transat A-330 did in fact lose cabin pressure. Some people who were on that flight were interviewed and described their experience as " very uncomfortable." During a situation like that one, cabin pressure increases because as the plane descends, the atmosphere becomes denser. If there is no fuel to power the APU and maintain a constant atmosheric pressure in the cabin, its pressure increases as the plane loses altitude.

You've got that a little bit gooned up, Saltman.

As Tri indicated, the first thing that's going to happen after a failure of all engines is that there will be no pack air flow. That means there is no air supplied to pressurize the aircraft cabin. The pressurization system senses this condition and the outflow valve cycles to fully closed in an attempt to trap as much air as possible. Again, as Tri indicated, no airplane is air tight. Depending on how old the airframe is, how many cycles are on it and how tight the door seals are the cabin will begin to depressurize (climb). We have to remember that while all of this is going on the flight crew will have begun their "drift down" procedure. Yes, folks, the airplane is still flying. It's now just a big glider. As the aircraft drifts down the cabin continues to climb. Somewhere through that whole evolution the cabin altitude will reach the point where the emergency masks automatically deploy. (The crew would, in all likelihood, already have their masks on.) And at some point the cabin altitude would meet the airplane altitude. When that occurs the cabin will begin descending at the same rate as the airplane. That's when it would get pretty uncomfortable for everyone in the airplane. By the way, APU's don't pressurize airplanes.

This type of event is extremely rare. It has happened in the past and I would imagine that it'll happen again in the future. The most likely scenario is an inadvertant encounter with volcanic ash.

Yes that sounds accurate, The RAT only provides the electrical power, so the cabin pressure will decrease.


I didn't know APUs didnt pressurise the planes, they provide pneumatic air which pressurises the hydraulics and allows bleed gor engine start. They also provide the air for Air conditioning, they do on all airbuses and Boeings.

This is extrememl rare, just need someone who is told not to wait for a spare part, put on the wrong one and the problem has been created. You mentioned the volcano scenario. That has happened a few times before, as I mentioned earlier the Speedbird 9 incident.

Regards,
Chris

I just have a few image caps to share that might reiterate Ranger's point..

http://webstu.db.erau.edu/~blandab6/747-1.JPG I didn't feel like looking up the operating limitations of the APU, so I'm not sure if it's possible or not, but I climbed the aircraft to FL300 with the APU running.

http://webstu.db.erau.edu/~blandab6/747-2.JPG Pneumatics schematic with all engines running.

http://webstu.db.erau.edu/~blandab6/747-3.JPG All engines failed, APU appears to be supplying bleed air

http://webstu.db.erau.edu/~blandab6/747-4.JPG APU bleed air off (the likely situation, assuming the APU can't be run at this altitude)

http://webstu.db.erau.edu/~blandab6/747-5.JPG As you can see, the outflow valves have moved to the fully closed position, and the cabin altitude is rising

http://webstu.db.erau.edu/~blandab6/747-6.JPG Eventually the cabin altitude rises above the level where oxygen is required

It's a matter of volume. It takes a LOT of bleed air to pressurize an airplane. The APU simply can't provide that sort of volume. Again, the APU is primarily designed to provide electricity and air on the ground. Through those capabilities the air conditioning can be operated for pax comfort (and more importantly, captain comfort), the lights, coffee pots and toilet flush motors will work and, if the airplane has electric hydraulic pumps, you can operate the hydraulic system.

I'm getting into an area that I'm not very familiar with since I don't fly two engine airplanes, but I think that ETOP's requirements include an APU that is capable of operating at very high altitudes. But, ETOPs are a whole different set of problems since you're talking about twin engine jets operating pretty good distances from a possible landing after an engine failure.

It is amazing how far a plane the size of an A330/767 can fly for every 1,000 feet of altitude they can fly, a few Kms for every 1000VS lost.

Regards,
Chris

Correct. From FAA:

And... who's going to predict the future?

PM

Let's call it a 50-50?

When I read this the other day I just added a post, as above. But when the incident occured on thursday, I thought about this topic, isn't this really ironic?
I know I didn't post this just after it happened, but I am glad that I didn't. Because PM has summed it up better, with the word choice.

Regards,
Chris

Well, Mr. Ranger, SIR, ah KNOW, YOU could land YOUR aircraft - with NO engines, whilst peeling an orange in your back pocket, with boxing gloves on the wrong hands. And, I aint being funny and I would not be nervous if I sat right seat from you - busy, oh yea, but cool as a cuke.

One of the first things I did with the A320, once I had got going and learned the aircraft, is analyse the non-normal op:

" DUAL ENGINE FAILURE"

This exercise is really one of numbers, its a numbers game.

Until that day arrives ( and Lordy, Lordy I sure hope it does not ) I am, and always will be, the winner, in this gameplan.

I saw an article in Flight International once, about a South American or Mexican B737 which had to land due to . . .no engines and s/he landed it in a field, alongside an embankment and everbody got off the aircraft and went home - and that was the end of that.

In the x-box, I mean the A320 - it goes something like this:

REMEMBER: BASE TO FINALS IS 1/2 D + 2500 FOR THE TURN
-------------------------------------------------------------------------
CONDITION
No gennys
RAT out
Alt Law
Auto Re-Light
Blue Hyd if no windmill
>>Manouvre with care<<
Capt ND ok, (new a/c only)
======================
ACTIONS
---------------
trim for 280
nav rose 80 nm
apt overlay (which is fine if VMC and overhead the airfield)
GO FOR APT> "Mayday x 3, callsign, position, intentions.
IF APU THEN TRK FPA 5 deg.
OPEN FL 00100
SEL SPEED GREEN DOT if no start
APU IF POSS
MANOUVRE WITH CARE

F/O MONITOR CAPT > then
ECAM
RE-START
280 KTS
APU < FL250
BLEED < FL200
RE-START
GREEN DOT
QRH
"CABIN CREW FORCED LANDING"
CAB ALT 20K
ECAM ONE SCREEN
IF NO FUEL, NO APU
((SUBTRACT 2500FT)) AND DOUBLE ALT
DOUBLE ALT = HALF D!
GO FOR:- RADAR VECTORS FOR A 5 deg APP
e.g. 24 MILES 12,000
8 MILES 4,000 etc.
<<1/2 D >>
Remember: FPA 5 DEG and DOUBLE ALT !!
ALT SET ABOVE CURRENT ALT
MID-DOWN-WIND 5 MILES GREEN DOT / 2500 LOSS IN TURN TO FINAL
*GRAVITY GEAR*
EG., IF 16,500 MID-DOWN-WIND THEN FINAL WILL BE 14,000 = 28d FINAL APPROACH
GLIDESLOPE CONFIG 1
"S" SPEED 180
SPEEDBRAKE IF FAST (Aircraft will tend to be fast rather than slow)
5 deg APP.
WHEN SURE OF GETTING IN, RE SELECT TO OR FLY TO A 3 deg APP
F/O CALLS ALT AGAINST DME PLUS ELEV TDZ
1,000 ft "CABIN CREW TAKE YOUR SEATS"
200 "BRACE BRACE"
YOU MAY NOT HAVE AUTOBRAKE, IF SO USE ALT BRAKING BUT WATCH FOR 1,000 PSI SO BRAKE GENTLY SO AS NOT TO LOCK THE WHEELS.
IF NO NOSEWHEEL STRG THEN USE RUDDER AND SHOULD BE ABLE TO TAXI CLEAR OF THE RUNWAY, AND ASK FOR A TOW IN - BY WHICH TIME WHO GIVES A MONKEYS ANYWAY, YOU ARE DOWN, WELL DONE.
"PASSENGERS PLEASE REMAIN SEATED"
"DOORS MANUAL" (CHECK ALT)

====you will ALWAYS land the aircraft.

Speedbird 9 - thats Lon to Aus via Bangcock iinnit? (Or is it Speedcock to Bangbird. . ?, I can never get it right. . )

Ask Sully.

...................

Make no diff, the result would be the same - cool choice of Landing area though - he may have made the home of the Falcon - but only with few feet to spare and it would have been harder than squashy, guaranteed, water that was one lonnnnnnnnng runway (albeit wet and containing bridges) flipping over the bridge was cool.

I do know that on a 767, a small propeller comes down to give you a little control, though I don't know what it powers.

What you mean is called the RAT (Ram Air Turbine). It produces hydraulic power via a pump . The hydraulic power is used for the controle and to produce electric power for the necessary systems.

Thanks!