This IFALPA Briefing Leaflet, produced with Boeing, addresses proper rudder use on all Boeing and McDonnell Douglas transport aircraft models. It was prompted by the NTSB’s investigation into the American Airlines Flight 587 crash, which found that sequential full opposite rudder inputs can generate structural loads beyond certification requirements. Boeing’s primary intended uses for the rudder are crosswind operations, directional control during takeoff or rollout, and engine failure — not aggressive maneuvering for roll control.
The leaflet explains the aerodynamics behind this risk: rudder deflection causes yaw, which generates sideslip, which in turn produces a secondary roll response. Because there’s a time lag between rudder input and the resulting roll, pilots can be surprised by an unexpected roll and mistakenly counter with another large opposite rudder input. This cyclic pattern can create rapidly growing “sequential over yaw” sideslip angles, and if the rudder is reversed at the peak of one of these oscillations, the combined aerodynamic and rudder-induced loads on the vertical stabilizer can exceed limit loads and even ultimate loads, risking structural failure — the mechanism believed responsible for the AA587 accident.
The document details Boeing’s structural certification standards, including the concept of design maneuvering speed (Va), the 1.5 safety factor built into rudder-related load cases, and how rudder-limiting systems reduce available deflection as airspeed increases (with pedal force and travel data given for common Boeing and Douglas models). It responds point-by-point to the NTSB’s four recommendations and includes an extensive Boeing FAQ addressing scenarios such as engine failure, jammed controls, wake turbulence, windshear recovery, and upset recovery — consistently emphasizing that full rudder is safe when used as designed (single-direction inputs for its primary purposes), but that rudder should generally not be used for roll control, especially during stalls, wake vortex encounters, or windshear recovery, where ailerons and spoilers should handle roll instead.
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