ok you're in the cruise and the pitots ice up. airspeed/mach will stay at current values. Crew decides to reduce to turbulence speed., thrust reduces to achieve this. As actual a/c speed reduces autopilot starts to slowly pitch the nose up to maintain altitude and whilst doing so applies nose up trim. Maybe the thrust even reduced to idle at this point.
This continues until ths is at aft limit (remember the indicated speed/mach are still at original cruise values but the actual aircraft speed is much lower. Autopilot and autothrust disengage and a/c reverts to Direct law giving immediate pitch up due trim and a/c gains circa 3,000 ft and then enters dynamic stall. Presumably this zoom would give a slight reduction in static pressure, therefore the indicated speeds would increase.
The aspect that really interests me is that neither crew member noticed the increasing pitch attitude as the speed was reducing. What would the flight director be commanding throughout all this? If during the zoom upwards it's showing fly down to regain the selected flight level this might explain the initial side stick forward to regain.
If neither pilot wasn't paying any attention to the attitude then where were they looking?
Coming back to the issue of pitots getting iced up I still don't understand with modern design why this is a problem. There are plenty of other jet transports flying around the world where, as far as am aware, this has never happened. What is intrinsically different in the design of the system on this a/c?
Last edited by fireflybob; 30th May 2011 at 19:09.