Why do light aircraft stop their engines in mid-flight?

[RobM77]

I often hear light aircraft flying over our house, stopping their engine, then restarting it about 20 seconds later. Why is this? Is it an exercise that pilots perform routinely?

[Eric Mc]

Practising engine out?

I always assumed they were just throttling back to idle rather than turning them off completely.

[ndtman]

Probably so that they don't disturb your big boobed neighbour when she's sunbathing topless

[Dr Jekyll]

No, it certainly isn't routine. Even when practising the procedure for an engine failure the engine is usually left on idle.

It could be they are throttling back to idle to descend, or more likely such a small throttle opening it's inaudible from a distance. Light aircraft tend to climb on full throttle so if they are practicing climbing and descending it can sound as though the engine is starting and stopping.

[eharding]

RobM77 said:

I often hear light aircraft flying over our house, stopping their engine, then restarting it about 20 seconds later. Why is this? Is it an exercise that pilots perform routinely?

Unless in some form of motor glider, you wouldn't deliberately stop the engine (as there is always the outside chance it might not restart, and hence cause much vexation and embarrassment), but just bring it to idle - for stall/spin training or aerobatics.

[RobM77]

Eric Mc said:

Practising engine out?

This is what I was wondering. You usually hear the engine throttle back first, and then it goes completely silent for a period. Then, the engine comes back to life again at idle and they throttle up. I just heard a biplane do it over our house and it's something I've noticed all sorts of small aircraft doing in the past.

Eric Mc said:

I always assumed they were just throttling back to idle rather than turning them off completely.

I guess that's possible, but you can hear them very clearly at idle, and then it goes completely silent, so I think this is unlikely.

[CAPP0]

It will almost certainly be to do with pilot training, and as above it's probably a throttle back to idle not a shutdown. Stall recovery training, for example.

[this is my username]

It is almost unheard of for light aircraft to deliberately stop their engines in flight. What you are hearing is probably the throttle being brought back to idle - either to initiate a descent or as part of a "practice engine failure" drill being carried out in training.

[Ayahuasca]

I have heard them do that too, over a dry-ish lake bed. Always makes me look up. Once one - a micro lite - didn’t start again and it came swooping down and landed on the beach. Pilot turned out to be an Israeli F15 pilot so we had a good chat about that as I arranged for his ‘rescue’. He insisted on buying me and my mate beers afterwards and told the most appalling Jewish jokes. [/annecdote].

(He claimed to have come down due to contaminated fuel)

[this is my username]

CAPP0 said:

It will almost certainly be to do with pilot training, and as above it's probably a throttle back to idle not a shutdown. Stall recovery training, for example.

Standard stall recovery requires an increase in power rather than a decrease - I guess that you are referring to the setup when the aircraft might be flown at low power (to simulate an approach to land) and a stall induced which would then require an increase in power as part of the recovery?

Standard spin recovery involves power reduced to idle - but spin training is relatively unusual and generally undertaken at fairly high altitude.

[anonymous-user]

this is my username said:

It is almost unheard of for light aircraft to deliberately stop their engines in flight. What you are hearing is probably the throttle being brought back to idle - either to initiate a descent or as part of a "practice engine failure" drill being carried out in training.

Exactly, you just aren't hearing the engine when it's running on idle.

For PFLs (practiced forced landings) they will cut to idle, get the aircraft into the glide, find a nice looking field and get set for a false landing, then power up again and climb.

Alternatively, they could be practicing stalls, where they will cut to idle, keep pulling the stick back till the aircraft stalls, then recover by pushing the stick forward and getting the power on again.

I'm guessing you live in a relatively open area with lots of big, flat fields and have an airfield with a flying school nearby. Both of the above are part of the PPL syllabus.

[jjones]

Instructors love to set it to idle and say "looks like it's gone again", was always at least once per lesson sometimes more.

[RobM77]

Maybe that's it; aircraft engines are just a lot quieter at idle compared to slightly above idle?

What I'm hearing is a steady throttle back and the engine volume drops steadily (imagine the volume as 10, 9, 8, 7) and then it'll pause for a few seconds at what sounds like an idle speed (7, 7, 7), and then suddenly it'll go totally silent (0, 0, 0).

[Bill]

I grew up near Middle Wallop and they'd regularly practise over our house. I guess it was just because it was the edge of the village and there were plenty of large fields just in case.

We used to pretend we'd shot them down.

[anonymous-user]

RobM77 said:

What I'm hearing is a steady throttle back and the engine volume drops steadily (imagine the volume as 10, 9, 8, 7) and then it'll pause for a few seconds at what sounds like an idle speed (7, 7, 7), and then suddenly it'll go totally silent (0, 0, 0).

Possibly the sound of them climbing up to safe altitude, throttling back to cruise, then practicing stalling or PFLs.

[CAPP0]

this is my username said:

CAPP0 said:

It will almost certainly be to do with pilot training, and as above it's probably a throttle back to idle not a shutdown. Stall recovery training, for example.

Standard stall recovery requires an increase in power

Indeed, but you've got to initiate the stall first!

[Eric Mc]

Yep - I remember "chopping the throttle" when doing stall recovery practice.

[normalbloke]

Because hybrid, innit...

[JuniorD]

Small changes in wind speed and direction can also make the sound appear to intermittently drop off

[2fast748]

I hear apparent engine stops quite frequently as we get a lot of flight training over our village. They go quiet and then suddenly give it a big handful of throttle. I did hear an odd one a while ago were it went quiet and stayed quiet, so much so that I could hear the prop spinning (it was low!) and I thought it must be coming down but there were no reports of an accident so it must have come back on out my sight.