What happened
On 6 August 2006, a Letov LK-2M Sluka, registration G-MZOT, was conducting a private flight from Bucknall to North Coates. The pilot had previously completed a return flight to his home airfield and was flying in company with another microlight. As the aircraft approached North Coates, the pilot transmitted a radio message reporting a partial elevator failure and difficulty maintaining control.
During the approach, the aircraft performed a descending orbit at approximately 150 feet. Witnesses observed the aircraft appear to climb briefly before the nose pitched down into a near-vertical dive. The aircraft struck the ground near the airfield boundary, resulting in one fatality and the destruction of the aircraft. The impact was primarily borne by the engine and cockpit area.
The investigation
The AAIB investigation focused on the structural integrity of the aircraft's tail surfaces. Examination of the wreckage revealed that the bracing wires securing the left and right tailplanes to the vertical fin had become detached from the upper part of the fin.
Investigators found that the bolt used to secure the upper bracing-wire tangs was still in place, but the associated stiff nut had disappeared. The investigation noted that the right tailplane was significantly drooping, which had caused the elevator mechanism to disengage. While the aircraft's maintenance logs showed no recent work on these specific components, the investigation looked into the possibility of the nut loosening due to vibration or improper installation.
Findings
- The accident was caused by the loss of the nut on the tailplane upper bracing wire attachment to the fin.
- The loss of this nut led to a structural failure of the horizontal stabiliser.
- The detachment of the wires caused the right tailplane to drop, which disconnected the elevators and removed the aerodynamic downforce required for stability.
- The pilot likely did not realize the severity of the structural failure during the initial approach, as the attachment point was located at eye level and might have been obscured during a standard walk-round inspection if the tangs were flush with the fin.
- The loss of the nut could have been due to the use of an incorrect nut type or the nut becoming worn through excessive re-use.