FAA Airline Transport Pilot (ATM)Transport Aerodynamics and High-Altitude OperationsMedium
A T-tail transport airplane is inadvertently allowed to reach a very high angle of attack near the stall. The turbulent, separated wake from the wing and fuselage blankets the elevated horizontal stabilizer, drastically reducing elevator authority needed to lower the nose. This hazardous, potentially unrecoverable condition is known as:
- AMach tuck
- BDeep stall
- CSpiral instability
- DDutch roll
Show answer & explanationAnswer & explanation
Correct answer: B. Deep stall
On T-tail airplanes, at very high AOA the wing/fuselage wake can blanket the high-mounted horizontal stabilizer, robbing the elevator of effectiveness right when nose-down authority is most needed. This is called deep stall (or 'locked-in' stall) and can be aggravated by a nose-up pitching moment from wing wake immersion of the tail.
Why the other options are wrong
- A. Mach tuck is a high-speed nose-down tendency from aft CP shift, unrelated to low-speed stall.
- C. Spiral instability is a slow divergent turn, unrelated to stall/tail blanketing.
- D. Dutch roll is a coupled roll-yaw oscillation, not a stall condition.
Deep Stall (T-Tail)
A dangerous stalled condition on T-tail aircraft where the wing/fuselage wake blankets the horizontal stabilizer at high AOA, greatly reducing elevator effectiveness needed for recovery.
- Occurs primarily on T-tail configurations
- Wing wake blankets the elevated stabilizer
- Elevator loses authority to lower the nose
- Can become a stable, unrecoverable stall
Memory trick: Deep stall = tail 'stuck in the shadow' of the wing wake