The TSB asked Boeing if, when using the engineering simulation, it would have been possible for the PF to keep the aircraft on the runway using only the rudder pedals.
Additional simulations completed by Boeing consisted of modifying the rudder pedal inputs to attempt to keep the aircraft on the runway. Boeing ran 2 scenarios with the engineering simulations.
The first scenario consisted of an increase of right rudder pedal input (up to full rudder deflection) starting from a neutral position at 1953:13 (i.e., 3 seconds after the start of the uncommanded left veer). This time was chosen as it was the time at which right control-wheel input was applied instead of right rudder pedal. During the simulation, from 1953:13, an increase of right rudder pedal input was applied, reaching full rudder deflection at 1953:17; therefore a gradual application of rudder pedal was involved, with maximum pedal reached after 4 seconds. Rudder pedal was not released until the simulation was terminated. The jam is assumed to have released at 1953:18
Note 39 (
Appendix E).
The second scenario consisted of applying and holding full rudder pedal from 1953:19,
Note 40 exceeding the amount of rudder pedal input that was recorded on the FDR at that time, when the aircraft heading started to return to the runway heading. This rudder pedal input was held for approximately 3 seconds, until the aircraft was recovering back toward the runway centerline (
Appendix E).
These simulations showed, in both scenarios, that there would have been sufficient control available to prevent significant deviation from centerline. Rudder pedal only was used during the simulations. Additional directional control would have been available from differential braking or differential reverse thrust. Boeing simulations suggest that there was enough control power from the rudder pedals to keep the aircraft on the runway, assuming that the rate jam cleared at 1953:18, as explained above.