What happened
On April 23, 2019, an Embraer ERJ 170-200 STD, registration JA11FJ, was performing a scheduled takeoff from Yamagata Airport, bound for Prefectural Nagoya Airfield. The flight was carrying 60 passengers and four crew members.
As the aircraft began its takeoff roll, it started to veer toward the left side of the runway centerline. The pilot in command attempted to correct the direction by applying maximum right rudder input; however, the aircraft failed to respond to the pedals. Believing the deviation was due to a weathercock effect from a left tailwind, the pilot eventually decided to abort the takeoff approximately eight seconds into the roll.
During the aborted takeoff, the aircraft continued to deviate from the centerline and eventually ran off the side of the runway. The aircraft struck a Precision Approach Path Indicator (PAPI) light before coming to a stop in a nearby grass field. There were no injuries among the 64 people on board, though the aircraft sustained damage to its lower fuselage and nose tires.
The investigation
Investigators from the JTSB examined the aircraft's onboard maintenance computer and Quick Access Recorder (QAR) data. The investigation focused on the nosewheel steering system, which features two modes: a "Handle mode" for low-speed maneuvering and a "Pedal mode" for high-speed directional control.
Technical analysis revealed that the steering system was stuck in the Handle mode, even though the pilot was not pressing the steering handle down. This prevented the rudder pedals from controlling the nosewheel. Further inspection of the steering handle's microswitch showed that while it appeared mechanically normal, it was sending an electrical signal that kept the system engaged in Handle mode. Microscopic examination of the microswitch uncovered tiny metal particles and fibrous material near the contact points, though the exact origin of this debris could not be determined.
Findings
- The primary cause of the excursion was the aircraft's inability to maintain directional control via the rudder pedals during the takeoff roll.
- The steering system remained stuck in the Handle mode due to a microswitch malfunction, which prevented the transition to the Pedal mode.
- The pilot's decision to abort the takeoff was prompted by the loss of directional control, and the decision not to apply brakes was based on a judgment that running off the runway was already unavoidable.
- The aircraft's systems and pre-flight inspection procedures did not provide a clear way for the crew to detect that the steering mode was incorrectly set during the takeoff roll.