Originally Posted by dream747
Which leads me to the question, say for example, our aircraft has a stalling speed of 200kts. Suppose we're flying at FL350 and should the PFD display IAS/CAS and is reading 220kts (for example), the error due to compressibility is not corrected for and EAS is actually 200kts. Wouldn't this be a danger as the pilot would think that he's 20kts away from stalling the airplane without knowing that he's closer to the stall than he actually thinks?
The pilot normally doesn't have to consider the "stalling speed". He operates on the basis of minimum speeds recommended for operation such as V1; VR; V2; VREF; VFTO; VLS. These speeds provide a safe margin above the stall speed and are given to him in CAS for electronic displays driven by an Air Data Computer which corrects for errors in the pressure sensing system, or IAS for pneumatic indicators.
The stall speed at FL350 differs considerably from that at sealevel due to Mach effects other than CAS/EAS difference, see discussion on other threads.
regards,
HN39
EDIT:: Quote from FAR/JAR 25.103(a): The reference stall speed VSR is a calibrated airspeed ...