What happened
On May 26, 2002, a Grumman G 21A/JRF Goose (registration N4575C) was performing a landing at Knock International Airport following a flight from Weston, Ireland. During the landing rollout on Runway 27, the aircraft began to veer toward the right side of the runway. As the aircraft drifted, the left main undercarriage collapsed, causing the left wheel to separate from the airframe. The aircraft then departed the paved surface, with the left wingtip float making contact with the runway, before performing a ground loop back toward the runway edge. There were no injuries to the two crew members or the four passengers on board.
The investigation
The AAIU investigation examined the aircraft's maintenance records, wind conditions, and the flightcrew's decision-making process. Investigators analyzed anemograph data, which confirmed that the actual prevailing wind at the time of landing was approximately 350 degrees at 16 to 17 knots. The investigation also reviewed the mechanical state of the landing gear, identifying two specific defects in the left shock-strut: a surface defect on the sliding cylinder and a reduced thickness in the support housing of the center-point folding bolt. Furthermore, the investigation looked into the operational limitations set by the aircraft's private operator and the flightcrew's adherence to established crosswind limits.
Findings
- The primary cause of the accident was the use of a landing and rollout technique that was unsuitable for maintaining directional control given the prevailing crosswind conditions.
- The flightcrew failed to comply with verbal crosswind limitations previously established by both the private operator and an FAA instructor.
- The aircraft's undercarriage stability was compromised by the over-inflation of the shock-struts, which increased the aircraft's nose height and reduced the effective track width.
- The failure of the left undercarriage assembly was a direct consequence of the lateral forces generated when directional control was lost during the rollout.
- While the aircraft was generally well-maintained, the identified defects in the left shock-strut should have been repaired or replaced.