Since a wing always stalls at the same incidence, and the aeroplane is only interested in EAS, the stall will occur at a fairly constant EAS. However at the very high altitudes of which a jet is capable, the indicated stall speed increases. This is due to two things. Firstly, the compressibility correction, which forms part of the difference between ASIR (airspeed indicator reading; the uncorrected reading on an airspeed indicator) and EAS (the other parts being instrument error and position error), is larger in the EAS to ASIR direction due to the effect of Mach number. Secondly, the actual stall EAS speed increases due to Mach number effect on the wing. At very high altitude the EAS stall speed occurs at a significant Mach number (180 knots = 0.61 Mach number, for example); the pressure pattern is disturbed and a higher stall speed results. Courtesy D. P. Davies
