To put the engines into reverse thrust on most aircraft you have to pull them all the way back, and then up and over a hump. But beyond that for the vast majority of jets, in order to put the engines into reverse thrust the weight on wheels switch needs to be active. In other words, the plane has to be on the ground.…

Autopilot is required to fly in RVSM airspace. If you can’t fly in RVSM then you’re flying low, and burning much more fuel than usual. Or for longer routes, you can’t make it all. There’s a reason why the pilots want the autopilot fixed.