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1970-01-01

Yes that makes sense at a high level, but there must be a point of transition between calm air and a jet stream that makes the wings useless to the airplane for at least a few seconds.

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These sudden changes do indeed happen in stormy weather, as adjacent layers of air can move with different velocities relative to the ground (the technical term is “wind shear”). If an airplane climbs or descends through those it will look like your speed (relative to air) is suddenly increased or decreased by some amount and you would have to compensate. It’s also a bigger problem for large, heavy airplanes as you have more work to do to accelerate for a given amount of speed loss.

Jet stream boundary is usually not this sharp, and the airplane would fly much faster than the difference anyway.

It's relevant in practice when landing against head wind. You need to have extra speed to not stall when you enter the slower air near ground.

Do you mean landing with a tailwind? A headwind should allow the plane to create the same amount of lift it needs to avoid stalling at lower ground speeds.

Yes, that’s correct, but the headwind stops being so headwind-y near the ground, so your plane needs to go a bit faster to compensate for the loss of headwind-ness in the seconds before touchdown.

On the flip side you also get ground-effect when you are low to the ground where the high-pressure underneath the wing gets trapped against the ground creating a cushion of pressure increasing lift.

Which can be a bit of a challenge when trying to land, especially for aerodynamically efficient aircraft.

If you took a plane flying in still air and magically, instantaneously replaced all the air around it with a tail wind equal to its velocity then yes the plane would stall and fall out of the sky.

Fortunately that kind of instantaneous change doesn't happen in real life.

GO AROUND, WINDSHEAR AHEAD!

Indeed it does, that's effectively what turbulence is.

Presumably the plane would accelerate as it climbed through the velocity gradient, never falling to a point of negative air-relative airspeed.

Yes, the wings are useless once the air is moving close to the speed of the plane. Thankfully, we have jet engines that help planes move a lot faster than the 100-200 knots that jet streams can reach. They'll still affect the flight but only temporarily.

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