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Recently I watched a fascinating video of Cathay flight 780.

What interested me about the end of this incident is that the pilots opted to land the aircraft with the engine 1 still at 80%, over speeding with the flap setting (and not even setting full flaps for landing configuration), which was also covered in this question: Why didn’t the Captain of Cathay Pacific flight 780 shut down engine 1 and land with a more reasonable speed?

If it was me, (and I speak as someone who has roughly 1% of the flying time of the captain of this flight and 0% in that type :) ) - I would have got to a high altitude over the airport (maybe FL100) and then cut both engines, so that I could set up a full landing configuration before performing a glide approach.

The benefit of this would be landing at a normal speed. The downside is obvious - you only get one shot.

What is the 'correct' course of action if your throttle gets stuck on full (or close to it) power?

Bianfable
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Cloud
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    Also note: Flying a huge airliner without engines isn't exactly easy. You lose most electrical power and hydraulic pressure in most systems. There was another incident with an A330 (Air Transat 236, Mentour Video) that lost both engines and ended up with a landing that was very similar to the Cathay one. – Bianfable Oct 30 '23 at 15:10
  • After viewing MentourPilot's breakdown of the situation, I imagine the captain did not want to risk the unpredictable engine cutting out partway through a go-around; he figured he had brakes and could throw the functioning engine into reverse thrust upon touchdown, which he did. And he might not have trusted himself with a second Gimli Glider. – S. G. Nov 01 '23 at 19:40

3 Answers3

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Some WWI pilots had to deal with exactly that as normal operation, because the La Rhone rotary engine didn't have a throttle and you controlled the engine with ignition to taxi, descend, and land etc. Whenever the ignition was on, you were balls-to-the-wall.

So just shut the engine down with the mags, keep the mixture on, and glide to where you need to go. If you need power, switch on the mags on and off as required like you were in a Sopwith Camel. That's exactly what I would do.

You are likely to get nasty backfires when you put ignition on after being off a while, with all the unburnt fuel in the exhaust, depending on how leaky the engine's exhaust valves are, and might even blow out a muffler, but you're saving yourself, so who cares about that.

You could avoid the backfires by using the mixture to do the same thing instead of switching mags off and on, if you can live with the small lag in the input/result. I might use mixture when higher, then use the ignition to manage the engine on approach and cut the mixture for good when the runway is assured.

John K
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  • that's what's been advised at some point to the student pilot in this audio – user721108 Oct 31 '23 at 06:46
  • I presume that technique couldn't be replicated with a turbine engine? – MikeB Oct 31 '23 at 07:34
  • @MikeB No, the ignition is normally off for a turbine engine since you have a continuous flame. The only way to shut it down is to cut the fuel supply. Restarting it also takes significantly longer than a piston engine, plus you typically need a pneumatic source or high enough speed for windmilling. – Bianfable Oct 31 '23 at 08:08
  • @Bianfable would a turboprop shut down or be damaged if feathered at (stuck) full power? – user721108 Oct 31 '23 at 09:43
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    @jkztd Most turboprops have a free turbine for the propeller gearbox, which would slow down when feathered, but the gas generator would still run at full fuel flow. My guess is you'd overheat and damage the turbine pretty quickly and possibly create an engine fire. – Bianfable Oct 31 '23 at 09:58
  • The Vickers FB5 ('Gunbus') was controlled by blipping the mags on the Gnome monosoupape engine. – Michael Harvey Oct 31 '23 at 12:18
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    @Bianfable you would have to leave the power levers above Beta mode (somewhere above flight idle) and feather the prop and the prop load might keep the NG in check (or not). Also, as soon as you retard the power lever to flight idle, you normally enter Beta mode (Flight Beta) where fuel control switches to automatic governing of propeller RPM (Np governing) as the power lever takes over control of blade angle. So possibly a fuel control runaway in flight mode my be resolved by going into Beta, if the Np governing mode still works. – John K Oct 31 '23 at 16:12
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There is no single right answer to this, it depends on the airplane, the number of engines, and the power level of the stuck throttle. Most light singles have no hydraulics to power and your electrical system can run off the battery, if you're in an airliner it's a different story. In a light single with steam gauges half your instruments are usually powered by the engine, if you are in IMC you'd want to keep your engine on as long as possible, in visual conditions you may be more comfortable in a glide approach.

How draggy is your airplane? If I'm in a Cessna 172 with a throttle stuck at cruise power I'd be very comfortable keeping the engine on until I'm on short final because I know I can dirty it up by setting flaps 20 and side-slipping. A Diamond DA-40 is a much cleaner beast as it's design roots are in gliders, energy management becomes much more critical in that situation, I would have to kill the engine much further out in the approach.

GdD
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The "correct" course of action in any emergency situation is whichever course of action you deem to be most likely to result in the lowest chance of damage to people and property.

If I were flying a light single, which is where I have more or less the only real world experience, and the throttle stuck open I would have almost no option but to line up for a glide approach and cut the engine with by setting the mixture to lean. The reason for this is that I would have no way to land safely with full power - that aircraft cannot produce enough drag to overcome the power of the engine.

In an airliner the situation may be different. A single engine stuck at 80% with the other at or near idle may well be able to excerpt enough drag with flaps/slats/airbrakes to overcome the lift and land without too much chance of killing everyone on board. Ultimately it seems this is the option that has been taken in the example given.

Jamiec
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    Similar to yourself I have SEP real-world experience and would follow the same approach you detail above, but I'm wondering if there is any possibility of attempting to abuse the mixture control as a poor-man's throttle rather than fully cut the power. The possible advantage being that you get a little bit of comfort knowing that the engine is not fully cut off, meaning it might be easier to abort and go-around if you think necessary. I might give it a try in a flight-sim.... – Mick Waites Oct 31 '23 at 14:22
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    @MickWaites bear in mind some aircraft (including the one I fly) don't have a mixture – Cloud Nov 01 '23 at 10:06