5 ms·

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

by 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.
        skissane 2y ago
        > 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. I remember a decade or more ago I was on a US domestic flight - I forget exactly what, I think it was American from SFO to LAX - so I doubt it needed ETOPS. But the captain announced - while we were still at the gate - that he was getting an error in the cockpit saying the RAT was faulty. And he called maintenance, and they told him to try resetting something (a computer or circuit breaker or whatever) to see if that cleared the error - and when it didn’t, he announced we could not take off and would all have to go back into the terminal. Thankfully they had a spare plane a few gates over and they put us all on that (same crew, same passengers) so we only lost an hour or two.
        inferiorhuman 2y ago
        Right. In the context of this discussion ETOPS buys you significantly increased inspection and maintenance requirements. That's why I don't playing this game of telephone. Someone told someone else that something else did something else. Were everything to have unfolded as transcribed here there almost certainly would've been a high profile investigation. Back to your flight, both the FAA and EASA require airliners to have a minimum equipment list (MEL). It's entirely unrelated to ETOPS (overwater flights). This list describes what equipment is required to be functional, what you can fly without and when. What's on the list is all going to come down to what kind of plane we're talking about. Could be you're not allowed to fly without a functional RAT ever. Could be that you can fly without a RAT as long as something else (e.g. APU) is functional. Could be you can only make a certain number of flights with a non-op RAT. A real world example is that ATR 72 crash in Brazil recently. One of the PACKs (air conditioning / cabin pressurization) was not functioning on the accident plane. Per the MEL you can dispatch an ATR in that condition, but you're limited to a service ceiling of 17,000 ft. Unfortunately that put the flight in direct conflict with the weather.
- inferiorhuman 2y ago
  The RAT makes an extremely distinctive sound. You'd recognize it nearly instantly. However the RAT will not power everything. https://www.youtube.com/watch?v=KzejbxNj1hY https://www.youtube.com/watch?v=KzejbxNj1hY
  - wildzzz 2y ago
    That's cute, it sounds like a little Cessna
- fshbbdssbbgdd 2y ago
  Would you hear it from inside the plane? Even if it’s not as loud as the main engine, if it’s audible at all a lot of people would notice a change in pitch/tone. At least, I notice when the sounds the plane is making change even though I don’t know anything about the reason.
  - fphhotchips 2y ago
    I feel like it's not the RAT you'll notice from inside the plane, it will be the silence from the engines. That combined with at least a momentary flicker of the lighting (I'm not sure if a RAT on a 787 will run cabin lighting but I doubt it), and you'll know.
  - jszymborski 2y ago
    It's apparently quite loud > After starting the descent, the flight crew made an announcement to the passengers; however, unbeknownst to the flight crew, the noise generated by the RAT (because of its high rotation speed) prevented the passengers and the cabin crew from hearing the announcement. https://asn.flightsafety.org/wikibase/187755 https://asn.flightsafety.org/wikibase/187755
    - Filligree 2y ago
      Oww. Seems they got lucky. It always surprised me that there aren’t small, local lithium batteries to provide backup power for critical components like the smoke detectors. Is the risk of those catching fire considered too high?
      - jszymborski 2y ago
        I know next to nothing about planes, but I think another comment here suggested some newer planes do have a large Li-ion battery banks. That said, a household smoke detector runs on next to no power. Obviously not the same device but surely it can operate on the same principle.
      - mrguyorama 2y ago
        >It always surprised me that there aren’t small, local lithium batteries to provide backup power for critical components like the smoke detectors There is, well, only lithium on the 787. If all power generation is dead, then the most critical flight instruments and gauges get about 20-30 minutes of power from the plane's batteries, things like your backup old fashioned gauges, the engine computers, and maybe some basic flight computer on newer planes. The RAT is intended to keep flight surfaces operational when everything else is utterly fucked, so it usually produces the same kind of energy as whatever the primary flight control system uses, which until recently was hydraulic power. On civilian airliners they generate tens of kilowatts. Airliners do not want to carry around an EV sized battery for the extremely rare occasions when you lose all systems, because that's a waste of gas. The RAT provides the same functionality for lower weight. When the RAT is deployed, you do not care much whether a smoke detector is powered, you are already vectoring towards an attempted landing.
- happosai 2y ago
  Indeed unlikely to hear RAT deployed due to emergency. But they do deploy it sometimes on test flights after maintenance.
- rob74 2y ago
  Usually, when the RAT is really deployed because of an emergency, the jet engines will be a lot more silent (because they're not producing any power). Although I'm not really sure how loud a windmilling jet engine really is, and I somehow doubt there is a YouTube video of a plane landing with both engines disabled - but you never know...
mulmen 2y ago
Why would the Ran Air Turbine be time restricted? As long as the plane is moving there’s power.
- logifail 2y ago
  > Why would the Ran Air Turbine be time restricted? Gravity?
  - mulmen 2y ago
    But the turbine generates power to keep the plane flying. Why would it only work for 10 minutes? Certainly the flight time is a product of fuel level and altitude. Even if both engines fail the flight time would be a function of altitude. I don’t see how deployment of the RAT informs flight time.
    - chillel 2y ago
      It does not generate power to provide thrust; it generates power - using the airstream as the aircraft moves through the air - for the avionics and/or hydraulics.
      - mulmen 2y ago
        Yes, exactly.
- reportgunner 2y ago
  If the RAT could keep the plane flying indefinitely we would just be using RAT instead of fuel I suppose.
  - DiggyJohnson 2y ago
    /s? A generator or alternator powered directly by the engines is more efficient than towing a wind vane (still indirectly powered by the engines and/or the potential energy of the airplane) every single time. This discussion has nothing to do with engine out failure modes.
kashunstva 2y ago
> RAT … It is what you hear sometimes, when the aircraft is making a very shrill noise flying over your head. I’ve been around a lot of airplanes and I can’t say I’ve seen or heard a ram air turbine deployed in flight. There was a recent incident involving a Frontier Airlines flight in which the RAT was deployed when the aircraft was put in emergency electrical configuration. The deployment of the RAT would be quite rare.
DiggyJohnson 2y ago
The chances of you being on multiple commercial flights where the Ram Air Turbine are deployed is infinitesimal, no? Also, RAT can power limited systems indefinitely on most models, not all or limited systems for a limited amount of time.

by n_ary 2y ago

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.
      - skissane 2y ago
        > 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. I remember a decade or more ago I was on a US domestic flight - I forget exactly what, I think it was American from SFO to LAX - so I doubt it needed ETOPS. But the captain announced - while we were still at the gate - that he was getting an error in the cockpit saying the RAT was faulty. And he called maintenance, and they told him to try resetting something (a computer or circuit breaker or whatever) to see if that cleared the error - and when it didn’t, he announced we could not take off and would all have to go back into the terminal. Thankfully they had a spare plane a few gates over and they put us all on that (same crew, same passengers) so we only lost an hour or two.
        inferiorhuman 2y ago
        Right. In the context of this discussion ETOPS buys you significantly increased inspection and maintenance requirements. That's why I don't playing this game of telephone. Someone told someone else that something else did something else. Were everything to have unfolded as transcribed here there almost certainly would've been a high profile investigation. Back to your flight, both the FAA and EASA require airliners to have a minimum equipment list (MEL). It's entirely unrelated to ETOPS (overwater flights). This list describes what equipment is required to be functional, what you can fly without and when. What's on the list is all going to come down to what kind of plane we're talking about. Could be you're not allowed to fly without a functional RAT ever. Could be that you can fly without a RAT as long as something else (e.g. APU) is functional. Could be you can only make a certain number of flights with a non-op RAT. A real world example is that ATR 72 crash in Brazil recently. One of the PACKs (air conditioning / cabin pressurization) was not functioning on the accident plane. Per the MEL you can dispatch an ATR in that condition, but you're limited to a service ceiling of 17,000 ft. Unfortunately that put the flight in direct conflict with the weather.
inferiorhuman 2y ago
The RAT makes an extremely distinctive sound. You'd recognize it nearly instantly. However the RAT will not power everything. https://www.youtube.com/watch?v=KzejbxNj1hY https://www.youtube.com/watch?v=KzejbxNj1hY
- wildzzz 2y ago
  That's cute, it sounds like a little Cessna
fshbbdssbbgdd 2y ago
Would you hear it from inside the plane? Even if it’s not as loud as the main engine, if it’s audible at all a lot of people would notice a change in pitch/tone. At least, I notice when the sounds the plane is making change even though I don’t know anything about the reason.
- fphhotchips 2y ago
  I feel like it's not the RAT you'll notice from inside the plane, it will be the silence from the engines. That combined with at least a momentary flicker of the lighting (I'm not sure if a RAT on a 787 will run cabin lighting but I doubt it), and you'll know.
- jszymborski 2y ago
  It's apparently quite loud > After starting the descent, the flight crew made an announcement to the passengers; however, unbeknownst to the flight crew, the noise generated by the RAT (because of its high rotation speed) prevented the passengers and the cabin crew from hearing the announcement. https://asn.flightsafety.org/wikibase/187755 https://asn.flightsafety.org/wikibase/187755
  - Filligree 2y ago
    Oww. Seems they got lucky. It always surprised me that there aren’t small, local lithium batteries to provide backup power for critical components like the smoke detectors. Is the risk of those catching fire considered too high?
    - jszymborski 2y ago
      I know next to nothing about planes, but I think another comment here suggested some newer planes do have a large Li-ion battery banks. That said, a household smoke detector runs on next to no power. Obviously not the same device but surely it can operate on the same principle.
    - mrguyorama 2y ago
      >It always surprised me that there aren’t small, local lithium batteries to provide backup power for critical components like the smoke detectors There is, well, only lithium on the 787. If all power generation is dead, then the most critical flight instruments and gauges get about 20-30 minutes of power from the plane's batteries, things like your backup old fashioned gauges, the engine computers, and maybe some basic flight computer on newer planes. The RAT is intended to keep flight surfaces operational when everything else is utterly fucked, so it usually produces the same kind of energy as whatever the primary flight control system uses, which until recently was hydraulic power. On civilian airliners they generate tens of kilowatts. Airliners do not want to carry around an EV sized battery for the extremely rare occasions when you lose all systems, because that's a waste of gas. The RAT provides the same functionality for lower weight. When the RAT is deployed, you do not care much whether a smoke detector is powered, you are already vectoring towards an attempted landing.
happosai 2y ago
Indeed unlikely to hear RAT deployed due to emergency. But they do deploy it sometimes on test flights after maintenance.
rob74 2y ago
Usually, when the RAT is really deployed because of an emergency, the jet engines will be a lot more silent (because they're not producing any power). Although I'm not really sure how loud a windmilling jet engine really is, and I somehow doubt there is a YouTube video of a plane landing with both engines disabled - but you never know...

mulmen 2y ago

Why would the Ran Air Turbine be time restricted? As long as the plane is moving there’s power.

logifail 2y ago
> Why would the Ran Air Turbine be time restricted? Gravity?
- mulmen 2y ago
  But the turbine generates power to keep the plane flying. Why would it only work for 10 minutes? Certainly the flight time is a product of fuel level and altitude. Even if both engines fail the flight time would be a function of altitude. I don’t see how deployment of the RAT informs flight time.
  - chillel 2y ago
    It does not generate power to provide thrust; it generates power - using the airstream as the aircraft moves through the air - for the avionics and/or hydraulics.
    - mulmen 2y ago
      Yes, exactly.
reportgunner 2y ago
If the RAT could keep the plane flying indefinitely we would just be using RAT instead of fuel I suppose.
- DiggyJohnson 2y ago
  /s? A generator or alternator powered directly by the engines is more efficient than towing a wind vane (still indirectly powered by the engines and/or the potential energy of the airplane) every single time. This discussion has nothing to do with engine out failure modes.

kashunstva 2y ago

> RAT … It is what you hear sometimes, when the aircraft is making a very shrill noise flying over your head. I’ve been around a lot of airplanes and I can’t say I’ve seen or heard a ram air turbine deployed in flight. There was a recent incident involving a Frontier Airlines flight in which the RAT was deployed when the aircraft was put in emergency electrical configuration. The deployment of the RAT would be quite rare.

DiggyJohnson 2y ago

The chances of you being on multiple commercial flights where the Ram Air Turbine are deployed is infinitesimal, no? Also, RAT can power limited systems indefinitely on most models, not all or limited systems for a limited amount of time.