> "coffin corner" I watched a TV programme a couple of years ago talking about this on the U2 as the speeds were only a few knots apart and also varied with al

> "coffin corner" I watched a TV programme a couple of years ago talking about this on the U2 as the speeds were only a few knots apart and also varied with altitude and other factors. The image at https://i.stack.imgur.com/Lu2Xt.jpg https://i.stack.imgur.com/Lu2Xt.jpg shows the airspeed corridor the pilots have to fly through. It's constantly flying on a knife edge.