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I was speaking with a 787 pilot last Sunday, I told him that the week before when I was at an airport there were two pilots sitting next to me talking about how

I was speaking with a 787 pilot last Sunday, I told him that the week before when I was at an airport there were two pilots sitting next to me talking about how "This is the third bloody 787 rescue we've had this month... I can't believe we had full engine and <I think he said auxiliary?> failure at the same time" - I asked him if this is common and he said "I hear of it, but I haven't had that many major failures, but lots of little things - last time I flew in from <city> a few moments after we touched down we lost auxiliary power from the rear engine, all the cabin lighting went black along with a number of other things, thankfully we'd already significantly reduced speed and were straight and already lost most of the speed we were carrying, so we were fine and taxied to the disembark location, they had it up and flying again within the day - but it certainly was disconcerting to say the least". I will be slightly paraphrasing from memory there, but certainly was quite surprised how calm he was about the whole thing, there's no way I'd board one of those things.

Filligree 2y ago
APU failure maybe? That would be troublesome indeed; with no engines and no APU you'd lose most instrumentation and a lot of the hydraulics.
- smcleod 2y ago
  I thought the guy I was speaking mentioned something about instrumentation but I wasn't 100% sure and that sounded more serious so didn't mention it - but if the aux engine failing would do that - I guess that lines up!
- n_ary 2y ago
  There is also a RAT at the back that can be deployed to generate some power(~5-10 minutes max) in case of severe emergency in Air. It is what you hear sometimes, when the aircraft is making a very shrill noise flying over your head. However, if it is not a test flight, a RAT deployment should make you very uncomfortable and worried…
  - deleted 2y ago
    [deleted]
  - ortusdux 2y ago
    https://en.wikipedia.org/wiki/Ram_air_turbine https://en.wikipedia.org/wiki/Ram_air_turbine
  - iwontberude 2y ago
    I find it hard to believe that anyone reading this was within earshot of a plane in a severe emergency and heard this particular sound and since turbine engines are already quite shrill I am basically just sorta confused who your audience is for this suggestion.
    - rolandog 2y ago
      Username does not check out. Jokes aside... I'm certainly part of the intended audience: point me at an interesting rabbit hole, and there I gooo.
      - iwontberude 2y ago
        Haha I didn’t parse it that way but I can see how you thought that upon rereading. I just want to understand why we would hear the RAT when there wasn’t an emergency overhead. I supposed planes regularly test them?
        rogerrogerr 2y ago
        They don’t.
        inferiorhuman 2y ago
        I'm not going to bother slogging through everything to be able to speak in specifics for every airplane ever built, but: A RAT provides backup electrical and/or hydraulic power for control surfaces (and other goodies). A RAT would certainly be inspected during a heavy check and likely even during line checks (e.g. an "A" check or equivalent). How often is gonna depend on the airplane. But to suggest that a critical piece of equipment isn't checked regularly is just silly. Additionally, it's pretty much guaranteed that if an airplane comes with a RAT the RAT is required to be functional for ETOPS flights. That alone means you're gonna be inspecting it pretty frequently. ETOPS certification has three parts: airplane, airline, and humans. You'd want to look at the ETOPS Maintenance Document at whatever airline to be sure. Outside of Asia (where domestic widebody flights are still common) I'd guess many if not most 787 flights are ETOPS flights.
jiggawatts 2y ago
Modern two-engine planes like the 787 have an auxiliary power unit (APU) in the tail. This is a small turbine that runs a generator and a pump for the hydraulics. It’s typically only turned on when the plane is on the ground, or if there’s an emergency in mid-air. It is also needed to start the main engines so if the APU is faulty the plane will probably be stuck where it is. In theory a 787 can take off with just one engine but this is not very safe and wouldn’t be done in all but the most exceptional circumstances. There are variations on this depending on the plane model, of course. Some older planes can use an external starter for their engines, but I think that’s very rare now.
- thecosmicfrog 2y ago
  Aircraft with INOP APUs can generally be "air started" with a ground-based high-pressure air system. It's relatively common and I've been on a plane that had to do the procedure. It was entirely undramatic other than engines being started before the pushback, but I doubt most passengers even noticed. Now, interestingly, the 787 is a "bleedless" aircraft, so it doesn't use high-pressure air from the APU to spool up the engines. I believe it can use its hefty bank of lithium-ion batteries to start its engines if the APU (and associated electrical generator) is INOP. Not a pilot/engineer - just an enthusiast. Someone more au fait with the 787 might be able to correct me on the above.
  - hinkley 2y ago
    My understanding is that there was a push to modify the U shaped tow trucks they use to position planes to have a battery powered system to start the engines. The idea being that the APU isn't particularly clean burning, not compared to power plant emissions. It's been a long while since I've heard anything about that plan, for or against.
    - thecosmicfrog 2y ago
      Interesting! Although it'd (presumably) only be useful for the 787, short of heavy modification to existing aircraft. Even the Airbus A350, an aircraft from the same era, uses a traditional bleed system. If planes continue down the bleedless route I can see it happening.

Filligree 2y ago

APU failure maybe? That would be troublesome indeed; with no engines and no APU you'd lose most instrumentation and a lot of the hydraulics.

smcleod 2y ago
I thought the guy I was speaking mentioned something about instrumentation but I wasn't 100% sure and that sounded more serious so didn't mention it - but if the aux engine failing would do that - I guess that lines up!
n_ary 2y ago
There is also a RAT at the back that can be deployed to generate some power(~5-10 minutes max) in case of severe emergency in Air. It is what you hear sometimes, when the aircraft is making a very shrill noise flying over your head. However, if it is not a test flight, a RAT deployment should make you very uncomfortable and worried…
- deleted 2y ago
  [deleted]
- ortusdux 2y ago
  https://en.wikipedia.org/wiki/Ram_air_turbine https://en.wikipedia.org/wiki/Ram_air_turbine
- iwontberude 2y ago
  I find it hard to believe that anyone reading this was within earshot of a plane in a severe emergency and heard this particular sound and since turbine engines are already quite shrill I am basically just sorta confused who your audience is for this suggestion.
  - rolandog 2y ago
    Username does not check out. Jokes aside... I'm certainly part of the intended audience: point me at an interesting rabbit hole, and there I gooo.
    - iwontberude 2y ago
      Haha I didn’t parse it that way but I can see how you thought that upon rereading. I just want to understand why we would hear the RAT when there wasn’t an emergency overhead. I supposed planes regularly test them?
      - rogerrogerr 2y ago
        They don’t.
        inferiorhuman 2y ago
        I'm not going to bother slogging through everything to be able to speak in specifics for every airplane ever built, but: A RAT provides backup electrical and/or hydraulic power for control surfaces (and other goodies). A RAT would certainly be inspected during a heavy check and likely even during line checks (e.g. an "A" check or equivalent). How often is gonna depend on the airplane. But to suggest that a critical piece of equipment isn't checked regularly is just silly. Additionally, it's pretty much guaranteed that if an airplane comes with a RAT the RAT is required to be functional for ETOPS flights. That alone means you're gonna be inspecting it pretty frequently. ETOPS certification has three parts: airplane, airline, and humans. You'd want to look at the ETOPS Maintenance Document at whatever airline to be sure. Outside of Asia (where domestic widebody flights are still common) I'd guess many if not most 787 flights are ETOPS flights.

jiggawatts 2y ago

Modern two-engine planes like the 787 have an auxiliary power unit (APU) in the tail. This is a small turbine that runs a generator and a pump for the hydraulics. It’s typically only turned on when the plane is on the ground, or if there’s an emergency in mid-air. It is also needed to start the main engines so if the APU is faulty the plane will probably be stuck where it is. In theory a 787 can take off with just one engine but this is not very safe and wouldn’t be done in all but the most exceptional circumstances. There are variations on this depending on the plane model, of course. Some older planes can use an external starter for their engines, but I think that’s very rare now.

thecosmicfrog 2y ago
Aircraft with INOP APUs can generally be "air started" with a ground-based high-pressure air system. It's relatively common and I've been on a plane that had to do the procedure. It was entirely undramatic other than engines being started before the pushback, but I doubt most passengers even noticed. Now, interestingly, the 787 is a "bleedless" aircraft, so it doesn't use high-pressure air from the APU to spool up the engines. I believe it can use its hefty bank of lithium-ion batteries to start its engines if the APU (and associated electrical generator) is INOP. Not a pilot/engineer - just an enthusiast. Someone more au fait with the 787 might be able to correct me on the above.
- hinkley 2y ago
  My understanding is that there was a push to modify the U shaped tow trucks they use to position planes to have a battery powered system to start the engines. The idea being that the APU isn't particularly clean burning, not compared to power plant emissions. It's been a long while since I've heard anything about that plan, for or against.
  - thecosmicfrog 2y ago
    Interesting! Although it'd (presumably) only be useful for the 787, short of heavy modification to existing aircraft. Even the Airbus A350, an aircraft from the same era, uses a traditional bleed system. If planes continue down the bleedless route I can see it happening.