Thanks. Is the normal Vref of 1.3 x Vs0 based on IAS or CAS?
One thought that crossed my mind was that if the air speed indicator was to suffer from large errors at the lower end of the speed range then the 33 KIAS Vs0 may be well below the Calibrated stalling speed.
If this is the case then the 61 KIAS approach speed may actually be 1.3 x the Calibrated Vs0.