What happened
On 29 July 2004, a DH82A Tiger Moth, registration G-APAO, was performing a training flight at Duxford Aerodrome when it struck a runway edge marker during a baulked landing. The aircraft was operating on a temporary grass runway, which had been established to accommodate an upcoming event at the airfield.
During the landing attempt, a gust of wind caused the aircraft to drift toward the left edge of the runway. The pilot applied power to initiate a go-around; however, while maintaining a three-point attitude to gain altitude, the right main landing gear collided with a 'Tribox' marker. The impact caused the aircraft to decelerate abruptly, forcing the pilot to abandon the go-around attempt. The aircraft subsequently ground-looped and came to rest on its right wing tip, left landing gear, and tail. There were no injuries to the pilot or the passenger on board.
The investigation
The AAIB investigation focused on the nature of the runway markings and the circumstances of the collision. It was noted that the temporary runway was narrower than the permanent grass runway. To mark the boundaries, the aerodrome operator used proprietary 'Tribox' markers. To prevent these markers from being moved by wind or propwash, the aerodrome fire service had partially filled the hollow plastic units with water.
The investigation examined the specifications of the 'Tribox' system against the requirements set out in Civil Aviation Publication (CAP) 168. The investigation also looked into the standards for frangibility and the adequacy of the guidance provided by the CAA regarding the use of such markers in cleared and graded areas.
Findings
- The collision with the runway marker caused the damage to the DH82A Tiger Moth and prevented a successful go-around.
- The 'Tribox' markers used did not satisfy CAP 168 requirements regarding maximum height or frangibility.
- The markers were significantly heavier than their empty weight because they had been partially filled with water for stability.
- The structural design of the markers, made of dense, thick-walled plastic, made them unlikely to yield or break upon impact.
Safety action
Following the investigation, the manufacturer of the 'Tribox' system updated its guidance, advising customers that while small amounts of water can prevent markers from blowing away, users must consider the impact on frangibility when placing products in cleared and graded areas.