Questions tagged [apu]
Auxiliary Power Unit. A device for providing alternate power to an aircraft, usually located in the aircraft's tail.
60
questions
3
votes
2answers
219 views
Could you start both A320 engines with APU BLEED on?
I've seen some procedures where one engine is started with APU bleed, then APU Bleed is turned off to avoid ingestion of non-desired gases and then the second engine is started with ENG 1 Bleed on.
...
3
votes
3answers
2k views
What powers the air-conditioning on commercial planes?
How is the air conditioning system on airliners powered? I expect that the air conditioning is powered by the APU powers, but I wonder if there are other power sources used like the main engines?
1
vote
1answer
175 views
How is an A320 on the ground kept cool inside if the APU fails?
What happens to the air conditioner when the APU is not available due to damage or it just fails?
Also adding that the airport does not have an air conditioning unit. Since it is above average sea ...
5
votes
3answers
595 views
Is the APU classified as a component of Airframe or Powerplant?
In the classification of systems and components on the aircraft - is an APU classified under the Airframe or the Powerplant?
0
votes
0answers
57 views
JFS vs APU (for fighter jets) [duplicate]
I know that many fighter jets such as the F16 and F22 use a JFS to get compressed air into the engine. However, I was also reading that an APU does this. Im very confused on what does what. Thank you.
5
votes
1answer
180 views
Why can APU supply both bleed air and electrical power up to 10.000 feet but bleed air alone up to 17000?
I am reading my company's FCOM and I saw there the following information.
APU Bleed + Electrical Load: Max Alt 10000 ft.
APU Bleed: Max Alt 17000 ft.
APU Electrical Load: Max Alt 41000 ft.
If APU ...
5
votes
1answer
141 views
Can APU start in-flight using RAT or battery power?
Is it possible for a passenger jet to start its APU using power from the RAT? If so, are there plausible benefits to doing so (like supplying hydraulic pressure to the wheel brakes)? Do modern ...
0
votes
1answer
158 views
How do aircraft batteries power the engine/APU? [duplicate]
I fail to understand how do batteries power up the jet engines/APU. Are they responsible for starting up the Ignition that ignites the air-fuel mixture? Or is there some other function which I'm ...
0
votes
0answers
71 views
Was the redesigned version of the One-Eleven's APU ever reapproved for inflight use?
The BAC One-Eleven, like most jetliners, has a turboshaft APU mounted in the tail section of the aircraft, which is mainly used on the ground, but, originally, could also be used during flight at ...
1
vote
1answer
504 views
How much power does the APU generate in a Boeing 737-300?
I have just watched Mayday episode 11, season 11, "Nowhere to Land" about TACA Flight 110 incident and I was more than surprised to learn that:
APU must be turned on,
APU needs about 5-10 minutes to ...
2
votes
1answer
203 views
Why does the APU Master Switch flash during a normal APU shutdown?
Hi all and Happy New Year!!!
I have a question relating to APU shutdown procedures on Airbus A320. During normal APU shutdown sequences, I noticed that after around 1m20s, the FAULT legend on APU ...
9
votes
1answer
5k views
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 ...
14
votes
3answers
4k views
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?
16
votes
2answers
7k views
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 ...
5
votes
1answer
236 views
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 ...
2
votes
0answers
568 views
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?
4
votes
1answer
494 views
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 ...
7
votes
3answers
821 views
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 ...
4
votes
1answer
795 views
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 ...
2
votes
1answer
874 views
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.
4
votes
2answers
2k views
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.
8
votes
2answers
2k views
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 ...
19
votes
3answers
4k views
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 ...
16
votes
1answer
1k views
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 ...
5
votes
1answer
523 views
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?
-1
votes
1answer
245 views
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 ...
3
votes
1answer
555 views
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?
2
votes
2answers
1k views
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 ...
8
votes
2answers
5k views
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 ...
2
votes
2answers
8k views
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.
4
votes
1answer
2k views
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?
4
votes
3answers
998 views
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?
4
votes
1answer
1k views
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 ...
41
votes
1answer
8k views
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 ...
16
votes
1answer
2k views
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.
32
votes
4answers
7k views
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.
8
votes
1answer
913 views
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 ...
1
vote
1answer
3k views
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?
7
votes
1answer
4k views
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?
9
votes
3answers
7k views
What is the APU actually used for?
What are the actual uses of the APU? When is it used? When does it go off?
16
votes
4answers
4k views
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 ...
15
votes
6answers
6k views
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 ...
4
votes
3answers
1k views
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 ...
7
votes
1answer
1k views
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 ...
6
votes
1answer
2k views
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 ...
4
votes
1answer
1k views
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 ...
1
vote
1answer
832 views
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.
11
votes
2answers
3k views
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, ...
15
votes
1answer
5k views
When do commercial flights turn off the APU?
On commercial flights do the pilots ever turn off the APU? Is it needed when flying?
5
votes
1answer
2k views
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 ...
