FAA Airline Transport Pilot (ATM)Transport Aerodynamics and High-Altitude OperationsMedium
During cruise at high altitude, a transport aircraft's yaw damper automatically deflects the rudder in small, rapid corrections in response to sensed yaw rate, without any pilot rudder input. What is the primary purpose of this automatic function?
- ATo trim the aircraft for asymmetric thrust after an engine failure
- BTo maintain a constant cabin pressurization schedule during turns
- CTo reduce Mach tuck by adjusting elevator trim automatically
- DTo damp dutch roll oscillations that are lightly damped at high altitude
Show answer & explanationAnswer & explanation
Correct answer: D. To damp dutch roll oscillations that are lightly damped at high altitude
Swept-wing transports have naturally low directional (yaw) damping at high altitude, making dutch roll oscillations persistent. The yaw damper senses yaw rate and commands small rudder inputs that oppose the oscillation, damping it out and improving ride quality and control.
Why the other options are wrong
- A. Rudder trim, not the yaw damper, is used for sustained asymmetric thrust trim.
- B. Cabin pressurization is unrelated to rudder or yaw damper function.
- C. Mach tuck is countered by the Mach trim system acting on the horizontal stabilizer, not the yaw damper.
Yaw Damper
An automatic flight control system that senses yaw rate and commands small rudder deflections to damp dutch roll oscillations, especially prevalent at high altitude in swept-wing transports.
- Uses a rate gyro to sense yaw motion.
- Commands proportional rudder deflection opposing the yaw rate.
- Essential for passenger comfort and controllability since dutch roll is lightly damped at altitude.
Memory trick: Yaw damper dances the rudder to squash the wiggle before you feel it