Kindly refer to the
slide presentation of the Bombardier representative, (especially slides # 7 & 8) describing the function of the Q400's ice protection system.
Also to the Bombardier slides describing the
stall protection system.
Do I understand the following three concepts correctly?:
- Both the Low Speed Cue (red bricks on the airspeed tape) and the Stick Shaker are driven by AOA -- not indicated airspeed.
- During icing conditions, the "REF SPEEDS" switch re-indexes the AOA stall-warning thresholds for Stick Shaker activation as well as for the Low Speed Cue. In other words, both the LSC and the Stick Shaker become more conservative when the "REF SPEEDS" switch is activated as the warning threshold is set to a lower AOA reference.
- The airspeed additives specified in the QRH are selected/entered manually by the pilots.
The above would appear to explain why the
QRH contains the following procedure and caution note:
Thus, it would appear that a failure to bug the "additive" speeds would result in the bugged speeds appearing
within the red-bricked band on the airspeed tape and the stick-shaker firing prior to the airspeed decreasing to the non-icing references.
This description of a Colgan Q400 stick-shaker incident in Vermont (during a line-check no less) appears to confirm the above thoughts.
Am I missing anything?