I'm completely ignorant about this matter, but why is it even possible to cut off fuel while taking off? Shouldn't there be a control that completely disables this? Is there actually a situation where cutting off both engines could be necessary and wouldn't lead to a catastrophe?
The general principle of aircraft control is that the pilot has the final say on how it is operated, not the designer, because you never know when you will need to take extraordinary measures. And the pilot generally prefers to return to the ground safely.
This is true for boing, but not true dor Airbus design philosophy. Airbus tends to limit the pilot control inout pushing the plane out of safe operation conditions. I'm not sure of it's possible/not possible to cut the engine fuel supply during take-off in any Airbus though.
I'm assuming fuel being cut off is salvageable if not in the middle of a densely populated city, especially if above a plain or water. So it could be the favorable option in case of an engine fire.
Also, such complexity would introduce additional points of failure - as a sister comment mentions, a faulty altimeter (or whatever sensor) could prevent you from cutting off fuel when you need to.
> if not in the middle of a densely populated city, especially if above a plain or water
What is on the ground below does not matter at that point - how far above that ground you are is what is important. More altitude is more time.
This flight was less than 200 meters up in the air. Sully's flight that you probably remember, that made a successful emergency landing on the river, was about 860 meters high, giving them much more time - about 3.5 minutes of glide time, vs. 32 seconds in the air, total, for the Air India flight.
Okay, maybe there is little hope of making an ideal landing. But the likelihood of it being a fatal accident is significantly reduced without the building in the equation, no?
Pretty sure nearly all runbooks have you first move the thrust lever to idle before cutting off fuel. That suggests you shouldn't be able to cut fuel independently of the throttle.
Sometimes? If you have enough altitude to trade for speed then after the cutoff you could glide to a hypothetical miraculously-placed runway right in front of you, vs. having fire quickly consume the entire plane if you don't cutoff..
You can physically cut off fuel without pulling the thrust lever to idle, because the two are separate controls.
However, it’s against procedure to do so - even dangerous. Throttle should always be at idle before pulling the cutoff switch, because otherwise excessive pressure can be created in the fuel system.
Essentially this is just a best practice, but there is no interlock between throttle and fuel cut off.
Then I got intrigued by your comment in case the throttle encoder fails. Turns out there is double redundancy on the throttle encoder (if one computer fails, the next one takes over), and if both fail the airplane will run on the last known setting at which point the only possible action that can be taken is to cut off the fuel (or keep it running with the last known throttle level).
In this regard both Boeing and Airbus follow the same implementation and there is no difference whatsoever between them.
Perhaps something they I have learned is that cutting off fuel during max throttle position (take off) may have damaged the fuel system of the Air India airplane because of big pressure in the lines and that may have interfered with the restart of the engines when the fuel valve was opened again.
