Had my recurrent sim session recently, something strange happened during one of the approaches. Flap 30, pressurisation problem, so standard approach. Passing approximately 1200ft the AT controls the speed in MCP SPD, the AP flies in VOR/LOC and GS. Selected speed in Vref30+5, engine anti ice on. Underspeed (A) starts blinking in the speed window, no thrust change from the A/T. Instructor freezes the sim. Wants to know why the minium speed reversion is active. His answer: "Engine anti ice is on, the stall warning logic is set for icing. Our approach speed is too low". Riiiiight.
Yeah, use of TAI at present or WAI at any time during the flight will raise the minimum speeds to account for icing on the aircraft, but unless flying with flaps 15 (where Vref Ice exists for that purpose) that shouldn't be an issue? Was it maybe just the sim becoming desyncronized / the simulated FMC computing a wrong Vref? If this would be possible one should have seen it on the real aircraft, no? All sounds fishy to me.
