|>>|| No. 20410
>It stands to argue that airplane air filters don't just suddenly fail without a hint of a warning, but that they have a scheduled lifespan, so that they can be replaced at scheduled routine checks and you don't have to keep your passengers going back into the departure lounge and waiting nearly four hours there. Or maybe that's just me and a limited grasp on airplane maintenance logistics.
Yes and no, basically. A sudden failure of all air filters on a plane is next to impossible, but everything on a plane is a complex ecosystem that is much more sensitive than a car or anything else like that, and the standards of safety are so much higher that almost anything not working 'properly' is cause to ground the plane - and as much as it means you end up with people annoyed they had to wait a few hours, it's inarguably the Right Thing To Do.
With the caveat that you likely never got the full or accurate story of your particular engineering delay - it's quite common to play down or lie about the problem to the public, because despite everyone who works in aviation knowing how rigorous the standards are, telling passengers "your plane wasn't airworthy an hour ago, but it's fine now, off you pop" is not advised. If the problem was specifically about a filter, it's likely that one of the many filters was blocked or more likely damaged (smoke in the cabin from a previous, unrelated problem will wreck a filter pretty quick), and since these filters are a large part of the system keeping you breathing up there in the air, you can't just fly with one knackered or not in place.
As for why they didn't have a stock of filters at IBZ, well, that's a question I've had to ask many times - why don't we have a spare cargo net on site, when they're quite prone to breaking on a heavy landing? But in the grand scheme of things, it's entirely impossible to have a spare of every single replaceable part on a plane, particularly when not every airport in the world has a <insert airline here> engineering department operating within it. You can imagine how expensive plane parts are, you can imagine how expensive real estate is at an international airport, at some point you can't just have a stack of every single part at every single place you fly to, particularly if you have no planes based there, that stop there overnight. And as you rightly say, air filters aren't commonly expected to fail catastrophically, so if one ever does, you're not likely to be in the right place to have a stack of them ready to go. And as you say, it's not as simple as popping in a filter, you need to run tests, and to run tests you need to run your engines, and in many airports that means you need to be towed out of the way so you're not causing an obstruction, it's a whole thing.
I've noticed Jet2 do seem to be the worst for having parts available on site, I've had to wait quite a few times for stuff to be flown or even driven in from other parts of the country. Smaller airlines with smaller engineering teams often carry common replacement parts with them on every flight, interestingly enough - the Flybe Dash 8's fly with an 'engineering kit' on board so they can deal with many problems, even in the back water local airports they end up in. But that comes at a cost of fuel and space, which on a typical short haul 737 is at a premium, whereas in a little Dash 8 the extra weight is often actually useful, because the Dash 8 is a terribly designed aircraft, but that's another story.
The most surprising thing about your story though is that the delay lasted that long - they do indeed usually fly in a plane from somewhere else, or choose to work it so you delay two flights by an hour and a half rather than one by three hours, because the compensation they have to pay out after anything over three hours is crippling. That seems a mistake on Jet2 ops' part (not that surprising) or perhaps they genuinely had all planes in the air - if they'd already used their spare planes for other delays or problems that night, for example. But usually they'll bend over backwards to get another plane out there. Just yesterday TUI, rather than take a three hour delay, flew a Dreamliner out to Corfu with 70 people on it (capacity is about 320) because doing that was still cheaper than paying everyone the compo for a three hour delay.
Once a plane is delayed for one thing, you tend to snowball. Your pilots and crew go out of hours and you need a fresh crew, maybe you have to wait for them to get to the airport if the only crew available was a standby crew. Then you might run into air traffic restrictions since you're not flying at your allotted time, flight plans expire and need replotted, the storm you were going to miss is now in the way, the ground team you were assigned is now elsewhere and you won't be getting a new one until you're 100% ready. All of this and more might have been a factor in what actually happened with your flight.
The bottom line though is that once engineering gets involved, customer satisfaction falls to the bottom of the list. Nobody is EVER going to put pressure on anyone involved in fixing and making the plane safe to fly. As soon as it's a safety issue, then the attitude by all should be "it's ready when it's ready", and as a passenger you should be very worried if they're trying to rush at that point. I assume you got some money back from such a long delay? This gets so expensive for the airlines that all I can say is that if you were delayed for that long, there was truly no other option. It is the single most expensive thing you can do, is delay a plane over three hours. There's a poster in my office outlining that it's about half a million quid cheaper to drive a truck into the side of a plane than it is to delay an EU flight over the compensation threshold.
I realise this was a lot of rambling and guesswork, but TL;DR it was probably a lot more complicated than they made it out to be.