Engine Failure, alternate power source Options

[Saltman66]

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?

[The Airbuser]

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)

[rjb4000]

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?

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...

[The Airbuser]

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

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

[rjb4000]

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...

[glnflwrs]

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

[trijetflyermd11]

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.

[Ranger]

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?

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

[Aspiring Boeing ...]

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

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

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

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.

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.

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

[The Airbuser]

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...

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...

[trijetflyermd11]

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...

[Saltman66]

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...

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.

[Ranger]

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.

[Aspiring Boeing ...]

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...

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

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.

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

[rjb4000]

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

[Ranger]

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.

[Aspiring Boeing ...]

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

[The Airbuser]

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.

Correct. From FAA:

Another criterion is that a required auxiliary power unit (APU) can start after the airplane has been at high altitude for several hours (cold-soaked) and can run reliably for the remainder of the flight.

[Piltdown Man]

If a 777 lost power to both engines

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

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

PM

[The Airbuser]

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

And... whose going to predict the future?

Let's call it a 50-50?