Roll upset recovery
Roll upset: uncommanded, possibly uncontrollable rolling moment from ice-disrupted airflow ahead of the ailerons.
- Cause (see
icing-effects-on-stall): ice ridges behind protected surfaces and asymmetric separation. Can auto-deflect an aileron with no pilot input. - Ridges: water droplets flow back before freezing. De-icing equipment cannot remove them.
Warning sign: abnormal or sloppy aileron control forces after the autopilot is disconnected in icing conditions.
- Can develop well before normal ice accretion symptoms are visible.
- Control forces can exceed pilot's ability to overcome.
Avoidance/recovery sequence (TC AIM AIR 2.12.3.3):
| Step | Action | Detail |
|---|---|---|
| (a) | Disengage autopilot | Can mask warning clues. Can self-disconnect once control forces exceed its limits, causing abrupt unusual attitude. |
| (b) | Reduce angle of attack by increasing speed | If turning, roll wings level. |
| (c) | Leave the flaps | Do not retract unless upper wing surface confirmed clear of ice. Retracting raises angle of attack at any given airspeed, can trigger upset. |
| (d) | Set appropriate power | Monitor airspeed and angle of attack. |
| (e) | Verify wing ice protection works symmetrically | Visually if possible, else follow aircraft flight manual. |
Flap contrast: tailplane stall (tailplane-stall) retracts flaps one setting. Roll upset leaves flaps.
Trap: applying tailplane-stall flap action (retract one setting) to roll upset instead of leaving flaps alone.
References
- TC AIM AIR 2.12.3.3