Questions tagged [apu]

Auxiliary Power Unit. A device for providing alternate power to an aircraft, usually located in the aircraft's tail.

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What does the PBY Catalina's APU look like?

I found some specifications of the PBY Catalina that mention an APU, but I did not find any other references to this APU. It seems logical that such a plane has an APU, and that this APU is not like ...
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Does the Antonov An-225 have an Auxiliary Power Unit (APU)?

Most APUs are installed in the rear, see the above image of an Airbus A380 as an example. On the An-225, no APU exhaust is visible at the rear of the aircraft. So does the An-225 have an APU, and if ...
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In what conditions is the APU used in midair?

In flight, engines provide all the needed energy (bleed air, hydraulic and electrical power). So the APU can be shut down shortly after engines are running. But I imagine that starting the APU in ...
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What powers an aircraft prior to the APU being switched on?

I know that APUs are power plants for non-propulsion related purposes and that they are turned on before takeoff. What powers an airplane prior to the APU being turned on?
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What prevents aircraft with a tailcone APU from using tail-mounted airbrakes?

The BAe 146 and Fokker F-28, which are virtually alone among jetliners in lacking thrust reversers, compensate by using large, tail-mounted airbrakes to help slow the aircraft during descent and ...
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What is the loud noise of a helicopter when the rotors are not yet moving?

What is the loud noise when a helicopter is ready to start flying, but the rotor is not yet rotating? For example at Trump's "chopper talk", when he is intercepted by reporters on the way to Marine ...
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What is meant by a “cold soak" of an APU?

What is the exact meaning of "cold soak" of an Auxiliary Power Unit (APU)? Is it to do with long flights at high altitude and the fuel getting cold? Will it affect the ignition of the APU? Can anyone ...
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Why is the APU located in the tail for almost all commercial aircraft?

I know there are planes whose APU (Auxiliary Power Unit) is located elsewhere, but for the most common commercial jet aircraft (A320, B737, B747, A330,...), the APU is located in the tail. Is there a ...
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What role did the RAT (Ram Air Turbine) play on US Airways flight 1549?

An article in June 2018 Flying Magazine regarding the RAT by a Rob Mark explains that Capt. Sullunberger deployed the RAT for additional power to guide the plane down to the safe ditching on the ...
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What is the source of emergency power for a 727?

I've found a couple of sources that state the 727's APU cannot be started while flying, as it draws air from the wheel well. It drew air from inside the wheel well, so it was only for use on the ...
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F-15 APU or JFS

Can a portable GTCP-85 series be used on an F-15? Or is there no capability to use an external APU. As I understand, F-15's use the JFS-190?
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When are the engine bleed air, APU and packs turned on in the B737?

When do I have to turn on the engine bleed air and APU? In videos I have seen that they are always on, and sometimes they turn them off after take-off. I also have the same question about the packs.
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Where is the inlet for the APU on a Fokker 70/100?

I can see the exhaust for the APU on a Fokker jet, but where is the inlet?
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Was the miracle on the Hudson saved exclusively by the APU?

In the film Sully, (staring Tom Hanks) the APU is switched on straight after both engines rollback, why was this step necessary; Airbus said this was the "15th thing" to do on the checklist. How or ...
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In normal condition, is the Airbus A320 APU fuel supplied by the main engine boost pump only?

I have a question relating to APU fuel system. As said in material, there are 2 system supplying fuel for APU to operate. 1st one is primary and 2nd one is secondary. In the 1st system or low ...
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Where is the APU fuel pump on the A320?

I'm looking for APU fuel pump location for A320 aircraft series. I'll be much appreciated if you provide a link to some images, schemes.
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Where is the APU in the case of an S-duct (like the L-1011)?

This question asks about the S-duct of the L-1011 Tristar. Fooot's answer shows a cut-out of the L-1011. Looking at this cut-out, I'm wondering: If the engine is at the 'normal' location of the APU, ...
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Where does the “APU Auto Shutdown” message appear?

I'm trying to find out if and where the "APU Auto Shutdown" message appears on the ECAM.
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What is the fuel source for the APU on a B737?

Where does the fuel come from that powers the APU on a 737? My understanding is that it is from the left front main fuel tank, but I've also heard, hearsay, it can have it's own source. I know that ...
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In BGA or ATR's what are the major causes of ODOR in Cabin or Smoke in Cabin? [closed]

In BGA or ATR's what are the major causes of ODOR in Cabin or Smoke in Cabin? There are some of the maintenance activities that are related to removal of Engines or APU. Removal reason: Smoke in cabin ...
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Can the APU provide emergency thrust?

By David Monniaux (Own work) [GFDL, CC-BY-SA-3.0 or CC BY-SA 2.0 fr], via Wikimedia Commons Many larger airplanes have gas turbine APUs (auxiliary power units). It seems that their exhaust is ...
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What is an “all-electric APU”?

Understand that the APS5000 used in the B787 is the first all-electric APU for large commercial aircraft. Source: http://www.pwc.ca/en/engines/auxiliary-power-units Sorry if this sounds too ...
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Why isn't the APU a standard diesel generator?

Why isn't the APU a standard diesel generator? Jet-A and diesel are interchangeable (with the addition of a lubricant). So why not use a cheaper piston engine as opposed to a jet turbine? V.S.
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Why do we have to perform a normal APU shutdown if a fuel spillage occurs?

I was reading in the limitations chapter of the A320 which stated that if a fuel spillage occurs we have to perform a normal APU shutdown what is the reason behind this?
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What is the difference between an APU and an ATS?

Is there a big difference between what an Auxiliary Power Unit (APU) and an Air Turbine Starter (ATS) system actually does? My understanding is that an APU provides power for the electrical systems ...
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Why do the jet turbines spin while the engines are turned off?

Why do the jet turbines spin while the engines are turned off? Is this as a result of the wind? Or are the turbines deliberately spun using the APU? If so what is the reason behind this?
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How are the services kept running on a plane without an APU? [duplicate]

I have seen several aircraft that do not have an operative APU, so how are lights, air, and other systems kept running?
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What is the purpose of the fin at the Boeing 787 APU exhaust?

The fin is located under the Boeing 787 APU exhaust as shown in the picture below. Does anybody know the application of this thing or it is used for 'guiding' the APU exhaust? Thanks.
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Why is powering on the APU so low on the A320 emergency checklist?

In the movie Sully we have this section of dialogue He wasn't following proper procedure at all. And I know because I had the QRH in my hands. He switched on the APU immediately after engine ...
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Why is the 787 tail cone made out of titanium?

In this question there is a drawing of a 787 that shows that the tail cone is made of titanium. Why is such a heavy-duty material like titanium required for the tail cone? I do not see how there ...
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What is this device protruding from the rear of this 787?

While looking at the photos from this question I noticed a small protrusion from the side of the plane. You can see it in the photo: and in the diagram from l@aeroalias answer: In the diagram it ...
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How are APUs started?

How are jet engines started? says that engines must be started from bleed air, which can come from the APU, another engine, or a huffer cart, or from windmilling. As far as I understand, APUs are ...
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Why would smoke enter the cabin if the batteries are switched off before the APU flap closes?

In the A320 FCOM SOPs securing if the APU flap doesn't fully close smoke may occur in the cabin in the next flight In the NORMAL PROCEDURES SECURING THE AIRCRAFT. It states that before switching off ...
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On the A320, why is it not recommended to use the HP ground unit when the APU Bleed is on?

Can someone explain what the HP ground unit is used for? And what damage happens to the bleed system if it is used?
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Why can't we use APU bleed air for wing anti ice on the A320?

The question says it all. While reading I came across this that we can under no circumstances use APU bleed air for supplying wing anti ice? Any reason?
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What is the APU actually used for?

What are the actual uses of the APU? When is it used? When does it go off?
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Is the Auxiliary Power Unit used after landing when ground power is available?

Assuming the airport provides ground power at the gate, will the Auxiliary Power Unit (APU) be started and used after landing? If not, I guess the engines will only be shut down when the Ground Power ...
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Can an APU exhaust make a contrail in flight?

I saw this picture in a local newspaper. My thoughts were, silly artists, that's the APU exhaust, it won't ever produce a trail like that during takeoff (or ever). Of course, the picture is clearly ...
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Why is the A400M APU on the side of the fuselage instead of the back?

As you can see in this picture the APU of the A400M is on the side under the right wing, including the RAM-Air-Turbine. Why is the A400M APU on the side of the fuselage instead of the back? Why is ...
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How does an ETOPS APU start in-flight?

An ETOPS APU has to be on-demand, i.e. must be able to start at any altitude. If it can't, then it's not shut down for the entire flight. Compared to a normal APU, what are the design differences ...
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How much electrical power is available in a Gulfstream G550 and from which power sources?

I'd like to understand what electrical power sources are available (engines? APU? GPU? Other?) on a larger jet like the G550, and how much power they can provide, depending on whether the airplane is ...
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What is the function of the hole at the rear of the airplane? [duplicate]

What is the function of the hole at the rear of a plane? I searched online but didn't get a satisfying answer.
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When do commercial flights turn off the APU?

On commercial flights do the pilots ever turn off the APU? Is it needed when flying?
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What type of engine/motor is used in aircraft APU?

Is the APU a mini-jet engine, or some other type of motor? I know its purpose is to provide power when the engines are off, but what kind of motor/engine is used to generate the power? I assume this ...
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What is this open panel at the rear of this airplane?

I saw this photo at another interesting question: There's an open square panel. What is it? P.S. Any tag suggestions are welcome. All I could think of was "tail". EDIT: are there any other tags for ...
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Can airliners operate without an operating APU?

As the APU (Auxiliary Power Unit) can be turned off when the engines are running, a functional APU may not be needed given you are able to start at least one engine. This question is in two parts: Is ...
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Where does the APU draw its intake air?

In an airliner, where does the APU draw its intake air? Is it a similar location for all airliners, or do different options exist?
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What could cause the APU on a Boeing 777 to fail and also trip the GPU?

I am a cargo aircraft loader at Heathrow and while we were offloading cargo, pallets and baggage containers from a Pakistan Airlines B777, the aircraft's Auxiliary Power Unit (APU) failed. It made ...
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BLEED FAULT lamp illumination under various conditions [closed]

In lots of commercial and defence aircrafts, bleed fault is annunciated because of mainly the following reasons: Overpressure/Overheat shut-off valve disagreement (i.e. failed open, failed closed) ...