What happened
On April 26, 2005, a Robin DR 400 - 140 B, registration F-GKQY, was performing a solo cross-country flight from Revel to Albi. During the landing roll on runway 09, the pilot experienced a sudden onset of nosewheel shimmy. The resulting oscillations caused the aircraft to become uncontrollable, leading the pilot to veer left and exit the runway onto the grass.
While taxiing through the grass, the pilot attempted to steer the aircraft back toward the runway. During this maneuver, the left wing of the aircraft struck the PAPI (Precision Approach Path Indicator) installation, causing damage to the wing structure.
The investigation
The investigation focused on the pilot's response to the nosewheel instability and the mechanical nature of the shimmy phenomenon. The pilot, a student with 36 total flight hours, noted that he had previously encountered this issue during training with an instructor. He reported that he attempted to mitigate the vibrations by applying symmetrical braking while simultaneously pulling the control column back to relieve pressure on the nosewheel.
Investigators examined the mechanics of the shimmy, noting that such unstable oscillations are often triggered by runway surface irregularities or uneven tire wear. The investigation also looked at how braking forces contribute to the instability, as heavy braking increases compression on the nosewheel, potentially exacerbating the effect.
Findings
- The primary cause of the excursion was the inadequate action taken to stop the shimmy phenomenon.
- The pilot's attempt to use heavy, symmetrical braking likely increased the compression forces on the nosewheel, thereby sustaining or worsening the oscillations.
- The sudden onset and physical discomfort caused by the shimmy contributed to the pilot's loss of effective directional control.