Originally Posted by
Pilot DAR
As my colleague mentioned, unless otherwise specified, stall speeds will be presented in calibrated airpseed, rather than indicated. Some flight manuals offer the courtesy of presenting it in both. Otherwise, this is a common error, a pilot believing that a stall is immanent based upon knowing Vso, but not as a CAS value, and watching the airpseed indicator to see it.
If anything it is the other way round. The IAS must be specified. You might see CAS or simply 'airpseed' in preamble such as specifications but in the part of the AFM where it counts the airspeeds must be indcated airspeed (even though one may see CAS alongside). I refer below to CS 23 as it appears to be identical to the old Part 23.
CS 23.1545 Airspeed indicator.
(a) Each airspeed indicator must be marked as specified in paragraph (b) of this section, with the marks located at the corresponding indicated airspeeds...
...a white arc with the lower limit at VS0 at the maximum weight,
CS 23.1581
(c) The units used in the Airplane Flight Manual must be the same as those marked on the appropriate instruments and placards.
(d) All Airplane Flight Manual operational airspeeds, unless otherwise specified, must be presented as indicated airspeeds.
