APU fire during takeoff?
Posted by Positive-Mulberry122@reddit | aviation | View on Reddit | 14 comments
Question from a curious non-pilot here: On monday, an A321neo had to return to athens shortly after take-off due to an APU fire indication. The plane was evacuated via the emergency slides lightly injuring three passengers. The youtube channel "Aeronewsgermany" produced a very interesting video featuring known facts, technical insight and footage from inside the plane.
In it, it is stated, that the APU is primarily used for engine startup. I am almost sure though, it is also used during take-off for the supply of packs.
While I think I know why, doesn't it pose an unnecessary additional safety risk to have a running jet engine running at the back of the plane during an already dynamic flight phase for just the added benefit of having air conditioning running during take-off ?
Fitzefitzefatze@reddit
The APU can be used to supply Packs during Take Off. But actually it is very rarely used to do so. Normally Packs are either supplied by engines, or a packless Take Off is carried out. Packs on APU is mostly used when climb Performance is not sufficient and you need them extra few percent of Power for the climb vs supplying Packs with them. So in 99% of Fights the APU is switched off shortly after the second engine start. Source: I am a 320 Pilot for Lufthansa I think in like 8 years of flying 320s i did maybe 2 Take offs with packs on APU.
PilotBurner44@reddit
I think it's highly subjective of where you fly and what airline you operate for. I work for a big US airline flying the 319-321, and I see a handful or more of APU-on takeoffs every summer when were departing somewhere hot and/or high like Las Vegas, Salt Lake City, Albuquerque, and a few places on Florida. We also don't do "packs off" take-offs per company procedures unless the APU is on MEL, which is pretty rare in my experience. I've only ever done one takeoff with the APU still running because we forgot to turn it off though.
Independent-Reveal86@reddit
Agree. I work for Air New Zealand and our take offs are either packs on, or packs on APU (if performance limited, never just packs off unless for an MEL.
Fitzefitzefatze@reddit
Of course it depends on company procedures and the environment you are operating in. For Lufthansa the go-to Take Off is Packs Off due to company procedures. Of course the cpt can Always decide to leave them running for passnger comfort. Which might have been the case in Athens as it will get pretty hot pretty fast wothout Packs, especially in an 321neo with more than 200 souls on Board. However even then the Take Off was most likely perfomed with packs on engines.
Independent-Reveal86@reddit
Having the APU running for take off is not an unnecessary fire risk. They are incredibly reliable. The fact that there has been one (1) recent incident involving an APU fire doesn’t change that.
Positive-Mulberry122@reddit (OP)
It does almost certainly pose some risk, however small. And I am aware of how small. Not considering MEL-items, it only provides bleed air though. So why not not do it?
ILikeFlyingMachines@reddit
It was most likely not running. Even when it's hot you usually just take off with packs running from the engine bleeds.
Bon-Bon-Boo@reddit
Unless they had an MEL like an Engine Generator inop. Then they would need the APU for an electrical source.
Donleon57@reddit
APU is usually shut down as soon as both engines run
Positive-Mulberry122@reddit (OP)
It usually is, but not always:
https://www.reddit.com/r/flightsim/s/y9gzu9mEfq
As per my understanding it is often left on during take-offs with high thrust demand to provide bleed air without straining the main engines. Last year, mentour pilot also posted a video suggesting a serious safety risk by supplying bleed air from the main engines during take-off. The event of an engine failure could dump large amounts of engine oil into the bleed air, possibly leading to pilot incapacitation or serious bodily injury.
https://youtu.be/swlVkYVSlIE?is=gCpNzOU5tw7uT1xR
Donleon57@reddit
We probably have to wait for the imterim and final report to be released
Positive-Mulberry122@reddit (OP)
Yes we do, this is just speculation and i don't want to imply this is what really happened.
TheStalledAviator@reddit
I guarantee you it was not left on.
Potatis-skal@reddit
Incident Airbus A321-271NX D-AIEA, Monday 11 May 2026