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Comment by VBprogrammer | Hacker News Reader

The fact that they where around 80 knots faster than they should have been probably helped a lot. That's a heck of a lot of excess energy.

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Pilot here, for anyone confused about the comment... some aircraft reach a speed where it is near a stall and cannot create a positive climb gradient when it touches down. Generally increasing angle of attack (angle the wings are with respect to the airflow) produces more lift. This works until a point is reached where the aircraft stalls (slow speed or high AOA, there is a curve). Many aircraft land near this airspeed, it produces a nice landing. But if you are faster than this airspeed, you can still pull up and create more angle of attack, create more lift, and take back off. So if you are landing fast you can easily pull up. This is exaggerated in fighter aircraft where we land at speeds that are faster than the stall threshold and a drastic pull up at landing can almost always cause a climb.

From what I can find the Airbus also requires the weight on wheels and the wheels speed sensors to have spun up before it will apply reverse thrust. Obviously the brakes also only work when the wheels are down. Auto-spoilers wouldn't deploy automatically also.

If I understand correctly does that mean they tried reversers, but they didn’t work so that’s why they initiated a go round?

The initial report indicates they did try to, but many planes won't allow reverse power unless some other indicator (landing gear down an in contact with the ground) says they're on the ground.

So maybe they'll go to idle but won't reverse, because reverse while in the air would be bad.

Fun fact, the Shuttle Training Aircraft actually used reverse thrust in the air to simulate the (probably terrifying) rate of descent of the real thing: https://en.wikipedia.org/wiki/Shuttle_Training_Aircraft

The excessive speed helped? Can you explain, I would imagine that going faster would cause more engine damage while being dragged.

But would also mean there was more energy to be converted to lift when the plane increased its attitude to take off again :)

Helped is probably the wrong word. I mean't that the aircraft had a lot of excess speed to get back into the air again, had it been at a normal approach speed you would probably have slowed down enough that it wouldn't have been possible to get it flying again.

More engine damage, probably.

But the excessive speed is what allowed the plane to lift off again.

There's a decision point past which your option to abort is no longer viable. Think of an overloaded plane attempting to take off. It may need 400 meters to brake. If the pilot continues to attempt to take off until only 200 meters of runway are left, braking is no longer an option.

In the case of the landing attempt above, reverse thrust and the very sketchy (ahem) landing configuration would typically bleed off too much speed to make a successful takeoff possible. Depending on the runway the implicit decision point might have been behind them virtually upon touchdown. With so much excess airspeed, though, while a safe stop was not possible they were still able to fly. It would have been a hell of a ride, though, and just thinking about abusing an airplane like that kind of blows my mind.

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