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Considering that airplanes are very noisy, could one routinely land them with the engines turned off, gliding onto the runway? Could the engines be started fast enough for an emergency situation?

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They could but the engine at idle you can't even hear it probably. Even an airliner isn't all that loud on approach. Anyway it's not really all that safe since most approaches start from further out than a power-off glide so the whole way pilots approach the airport would have to be changed to a "Baghdad" type approach like a glider pilot would use circling in from above. –  p1l0t Feb 25 at 0:39

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Not feasible. A start of each engine can take 30-60 seconds or longer and would require the APU (noisy). In some airplanes you lose the packs during start so you would impact pressurization. Additionally many engines have a required time at idle after start before significant thrust is applied. Lastly, with all engines offline, the airplane will be in some sort of essential power mode and many systems will be offline or unavailable.

You might then ask that we land at idle but that can present issues with spool up time before thrust is available.

One of the primary reason we land with a high flap setting is so that we have the drag to maintain approach speeds with the engines spooled up. This gives us near immediate power if we need it to go around.

I'm sure someone else can provide historical data from when idle approaches in jets were normal and specifics into why we don't do this today.

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Also many aircraft use thrust reversers to reduce the ground roll, no power means no thrust reverse and longer ground roll on landing. Next time you're out driving and approaching a set of traffic lights turn your engine off before you're stationary. How much harder is it to stop? Obviously don't try it for real, it's not safe, but hopefully you get the idea. –  Adrian Feb 25 at 15:12
@Adrian I didnt mention that since landing performance data assumes no reverser use. More problematic with all engines out in the EMB-145 is that you lose flaps and pressurization, and lots of instrumentation. We needed 3 generators online for full electronics and the APU only had one. –  casey Feb 25 at 15:16

Is it possible to land them with the engines off routinely?

Yes. Depending on the glide ratio of the aircraft, you most certainly can land them. And in flight training, we do practice this routinely, although we don't actually turn the engine off for safety reasons, merely reducing the power to idle. Technically, this is not the same thing, as the propeller is still turning and producing thrust, and of course the engine is on, producing noise, but it is certainly good to know how to land without an engine.

But I suspect you really were asking about the more important part of the question - should you, and is it safe?

Well, no, not really. You can check out this list of flights that required gliding. You'll notice that several incidents that required gliding were very succesful, and they glided for quite a long way. However, most notably for your question is the first flight on the list - a DC-3 on approach lost its engines and attempted to glide in. They failed to clear a mountain, and crashed, killing everyone aboard. If you were gliding into an airport, and suddenly needed power, it would take too long to restart.

Additionally, if weather conditions caused your first approach to be off, it would be definitely better to 'go around' than attempt to save a bad landing. Just watch the first landing of this video. It would not be possible to restart and engine before touchdown in that situation. Maybe it could be done earlier in the approach, but as the landing is a task-saturated phase of flight, you do not want to attempt it in those situations (in my training, we do not attempt to restart an engine under 800' AGL).

So in summary, yes it could be done, but no, you absolutely wouldn't want to do it because of the potential for needing instant power.

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Could you possibly clarify what "800' AGL" means? –  Audrius Meškauskas Feb 25 at 13:13
Sure. 800 feet above ground layer. So 800 feet above the ground, as opposed to 800 feet above sea level –  SSumner Feb 25 at 13:13

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