Because, what could possibly go wrong?
I think this is being misinterpreted. This method is already being utilized in 60 of the busiest airports in the US. The engines are never shut off. The airplane just makes a gradual long arc descent at minimum throttle in a holding pattern until its turn to land. The throttle is always available instantly in an emergency situation.
Can’t wait to see what happens
Watching autorotation practice at an air station was amazing. The pilots would have to shut their engine off at about 2000' and land those big helicopters with the pitch control alone. (control of the angle of the blades) They would drop like a rock and a few hundred feet off the ground would have to yank back on the stick making the blades look like a cup. A lot of them bounced pretty hard off the tarmac, but I never saw one pop a tire.
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