What happened
On September 12, 2020, a Learjet 35, registration LV-IYQ, was performing a non-scheduled medical transport flight from San Fernando International Airport to Formosa. During the takeoff roll on runway 05, the aircraft experienced a sudden loss of directional control. The crew, attempting to manage the deviation, aborted the takeoff. During the aborted procedure, the aircraft veered left, briefly crossing the safety strip before returning to the runway, and eventually came to a stop approximately 448 meters from the start of the takeoff roll within the left safety strip.
The incident resulted in no injuries to the crew, but the aircraft sustained minor damage, specifically deformations to the outer cover of the right main landing gear.
The investigation
The investigation focused on the aircraft's nose wheel steering system. Technical examinations conducted at a certified workshop revealed that the nose wheel steering control computer (P/N 800717-02) failed to properly limit the steering angle based on ground speed. Under normal operating conditions, the steering angle should be limited to approximately 8 degrees when speeds exceed 45 knots. However, the investigation established that the computer failed to restrict the movement of the nose wheel even as speed increased.
Investigators also reviewed air traffic control communications. While the tower notified the crew of an impending fire service alert, the crew initially indicated that the presence of the Rescue and Firefighting Service (SSEI) was unnecessary. The SSEI was eventually dispatched after airport personnel requested their presence as a precaution.
Findings
- The aircraft lost directional control during the initial phase of the takeoff roll.
- The nose wheel steering control computer failed to limit the steering angle relative to the aircraft's ground speed.
- This mechanical failure likely caused excessive steering corrections, leading to an uncontrolled zigzag motion and the subsequent runway excursion.
- There was a delay in the activation of the airport's fire services because the tower waited for crew confirmation after the crew initially declined assistance.