Tailplane stall mechanism and recovery

Tailplane stall: nose-down pitch upset from ice on the horizontal stabilizer, not the wing. Ice-disrupted airflow separates over it. It stops producing the download that balances the aircraft, so the nose drops (AC 700-031 App.B s.4.0(1), s.4.1(1)).

Recovery vs wing stall:

Warning and speed (App.B s.4.0(3), (4)):

• No warning: no stick shaker, stall horn, or buffet.
• Pitch-down can be fast and uncontrollable.
• Occurs well above 1G stall speed, typically near flap limit speed.

Most likely (App.B s.4.0(5)): flaps extended to landing position, combined with any of:

• Nose-down pitching manoeuvre
• Airspeed changes
• Power changes
• Turbulence

Aggravating factors:

• Forward CG (App.B s.4.1(3); mechanism in cg-load-distribution-limits).
• Unpowered elevators (more prone): nose-down motion can trigger aerodynamic overbalance, self-deflecting the elevator further nose-down, hard to overcome (App.B s.4.0(1), s.4.1(5)).
• Any flap setting: airspeed above manufacturer's recommendation plus uncleared tailplane ice may cause stall and uncontrollable nose-down pitch (TC AIM AIR 2.12.3.4 WARNING (a)).

Ice hides there first: thin tailplane airfoil can ice before wing ice is visible (App.B s.4.1(2)).

Impending-stall clues:

• Sudden elevator force change (moves nose-down if not restrained)
• Elevator pulsing or oscillation
• Abnormal nose-down trim change or reduced elevator effectiveness (autopilot can mask this)
• Forward control-column movement when power changes (App.B s.4.2(1))
• Any other abnormal pitch anomaly, possibly leading to pilot-induced oscillations (TC AIM AIR 2.12.3.4(c))

Recovery (App.B s.4.4(1); TC AIM AIR 2.12.3.4(b)):

1. Disengage autopilot.
2. Resist or restrain nose-down elevator motion.
3. Onset after flap extension: retract flaps one setting, increase airspeed as appropriate to the reduced setting.
4. Onset after power change: restore previous power.

Trap: treating it like a wing stall and pushing forward deepens the upset.

Practice