Icing effects on stall
Ice changes how the wing stalls, not just how it flies. Cuts lift at given angle of attack, adds drag and weight (AC 700-031 App. 5 s.1.1(a)).
| Effect | Detail | Cite |
|---|---|---|
| Stall speed up, critical AoA down | Ice alters airfoil shape, disrupts airflow. Stalls at higher speed, lower AoA than clean wing | App. 5 s.1.1(d) |
| No warning | Abrupt stall without normal aerodynamic warnings. Can occur before stall-warning systems (e.g. stick shakers) activate | App. 5 s.1.1(e) |
| Amount does not predict danger | Small rough ice can hurt more than large smooth ice. Drag can jump dramatically on some wings even when ice looks insignificant | App. 5 s.1.1(4) |
| Escalates fast | Large airspeed loss possible within minutes of entering icing. Buffet, vibration, sluggish or oversensitive controls signal worsening | App. 5 s.1.1(3) |
Roll upset (uncommanded, possibly uncontrollable rolling moment; TC AIM AIR 2.12.3.3):
- Asymmetric stall: ice-disrupted airflow separates unevenly. One wing can stall first and roll aircraft into upset, instead of clean-wing nose-down break (App. 5 s.2.0(2)).
- Control forces: may exceed pilot's physical ability to overcome (TC AIM AIR 2.12.3.3).
- Ice ridge: ridge ahead of ailerons, more likely with supercooled large droplets (SLD), can deflect an aileron with no pilot input, causing roll upset (App. 5 s.2.0(3)).
- Conditions: linked to SLD. Theoretically also possible in conventional icing just slightly below 0°C (TC AIM AIR 2.12.3.3).
Trap: expecting usual buffet-then-break stall warning. Iced wing can stall abruptly, no warning, and roll one way instead of pitching straight down.
References
- AC 700-031 App. 5 s.1.1, s.2.0
- TC AIM AIR 2.12.3.3