JohnM62

Two BA flights today, one on an A319 the other on an A320 Neo, both had APUs not working. Coincidence or is there a general issue with Airbus APUs?

c1223

There's less incentive for the APU to be working as the aircraft can usually be dispatched with it INOP, unlike one of the engines! It isn't uncommon and part of the reason that air carts are available on the ground. From a maintenance point of view, APUs are a "minimum equipment list" (MEL) item - the aircraft can operate without it. So there's no urgency to pull the aicraft from the schedule as it'll just create a load of other problems from a scheduling point of view.

ETOPS comes into play if you're flying over large bodies of water, however for BA on their shorthaul/midhaul fleet, that isn't really an issue.

rapidex

Apu situation usually deteriorates over a busy summer season, then they gradually get fixed in the quieter winter. You having 2 out on consecutive flights is a bit like playing black or red on roulette. The chances of one or the other decrease the more times it comes up.

DeathSlam

That's not how it works. Once you have hit red 3 times, the chance of it coming up red next time is still 50:50 (ish).
But before anything had happened the chances of getting red four times in a row was only 1 in 16.
So OP has exactly the same chance of getting a faulty APU on their next flight as they did before they were unlucky enough to hit a statistical wibble.

Sigwx

As C1223 correctly states, an inop APU can usually be dispatched via the MEL/DDG. An ETOPS rated 320/321 would certainly need it, however even some long haul types can fly without and still comply with ETOPS dispatch requirements. It does generally cause a nuisance for getting away on time and making the cabin environment more pleasant temperature wise on warmer of very cold days pre engine start, on short haul it is true that the defect would be deferred to get a service away and keep a frame on the line prior to hanger input for repair/replacement as it is not vital.

JohnM62

The aircraft for my return flight was very late arriving at Aberdeen due partly to an unspecified issue with ground equipment at Heathrow. Then we were delayed further because the ground starter they were using in the absence of an APU wasn't powerful enough to start the engines. Which made me think the Heathrow problem could have been the same.

Incidentally I don't think Concorde had an APU at all.

Waterhorse

This is quite an interesting point, in that a lack of understanding of this affects our attitude to risk. NASA first really described the effect when they investigated the first shuttle disaster. The first time we undertake a risky activity we think about and make a judgement as to the risk (that judgment may or may not be correct). The next time we undertake the same activity we are less cautious as to the risk as we have already made our judgment, undertaken the risky activity and been successful. The third time, we make no risk assessment as we have “normalised” the risk - after all we have done this risky activity “loads of times” and it has been fine. However, the level of risk remains identical each and every time we undertake the activity - getting away with it does not change the risk.

To put it in gambling terms, if you toss a coin it’s a 50/50 chance it comes up heads - every time you toss that coin. Should you have already tossed that coin 19 times and it’s come up heads every time doesn’t change the chance it’ll be heads again away from 50/50. Before you started tossing the coin, the chances of 20 heads in a row is a tiny tiny chance but for each coin toss it’s a 50/50.

So with risk, it’s identical every time, unlike the coin toss, with risk we assume that there is no risk if we have gotten away with a few times ( and it really is only 3 times) before we normalise the risk to zero. NASA, in their own wonderful way came up with a phrase for this, it is called Normalising Deviance.

Waterhorse

Regarding APU issues, yes the aircraft can be dispatched with a unserviceable APU, though it is still up to the commander to accept the aircraft as fit for service. On a very hot day, in the summer, I was supposed to use an A319 with a U/S APU and rejected it for service. Pre-boarding the internal temperature was 38c, there was no ground air or air cart to cool the aircraft, nor could we start an engine to get some cooling air. We were going to Rome IIRC and I had just walked through the departure lounge. There were at least 6 babes in arms, so I decided it was not safe to put them into that environment - a straight safety issue. So it’s not a given that a broken APU is always okay

DeathSlam

A sad example of this was an interview with a young motorbike rider who, when justify his extreme riding said "Well I haven't died yet". Then it happened.

KARFA

G-TTNN has a broken APU today

Kruisler

This.
Recently flew from Dallas in an A380 with an inop APU... Flight delayed by 1hr, cabin very hot on boarding until the engines were on.

flarmip

G-NEOW making rather fewer "neow" noises than usual, as its APU was also U/S yesterday. I clocked it as soon as I saw the power cart on the ramp, having noted the curiously lengthy turnrounds over the past couple of days. The Captain apologised for the start-up delay and heat due to the "air conditioning unit in the back of the plane" being broken. Not quite accurate of course, but an entirely understandable simplification to get the point across.

JohnM62

TTNN Was the one I flew from Aberdeen on.

BWBriscoe

What’s the procedure here, start one engine before pushback?

KARFA

yes, start one engine on stand using the air cart, then push back, then start the other engine using bleed air from the first engine.