No, "Cruising at altitude is not that hard." isn't correct. That is the coffin corner: https://en.wikipedia.org/wiki/Coffin_corner_(aerodynamics) https://en.wi

No, "Cruising at altitude is not that hard." isn't correct. That is the coffin corner: https://en.wikipedia.org/wiki/Coffin_corner_(aerodynamics) https://en.wikipedia.org/wiki/Coffin_corner_(aerodynamics) Being near the coffin corner is often desirable for performance reasons, but it sure isn't easy.