What happened
On the evening of May 30, 1998, a RANS S-12 microlight, registration D-MLAB, was participating in the Sligo Treasure Hunt, an event held as part of the annual Sligo Airport "Fly In" weekend. The aircraft was flying a planned route near Sligo, passing over local landmarks such as Coney Island and Rosses Point.
Shortly after 18:00 hours, the aircraft's flight path took it over the tidal estuary of Sligo Bay. Witnesses observed the aircraft flying at a low altitude, noting unusual engine sounds and a puff of smoke. The pilot attempted to communicate with Air Traffic Control, stating there was trouble with the wind, but the transmission was cut short. The aircraft then entered a steep, near-vertical nose-dive, impacting the firm sand of the estuary approximately one kilometer west of Gibraltar Point. The impact was severe, and both the pilot and the passenger sustained fatal injuries. The wreckage was submerged by the incoming tide shortly after the accident, which delayed the technical investigation until the following morning.
The investigation
Investigators examined the wreckage of D-MLCT and interviewed several eyewitnesses, including local residents and fishermen. The investigation focused on the mechanical state of the Rotax 582 engine and the propeller assembly.
Technical analysis revealed that the aircraft was equipped with incorrect propeller blades; specifically, ground-adjustable blades had been installed on a hub designed for in-flight pitch adjustment. This mismatch could lead to a loss of pitch control and increased vibration. Furthermore, investigators noted that a fuel cap from the left wing tank was missing from the wreckage. The investigation also looked into the functionality of the Ballistic Recovery System (BRS), finding that the safety pin had not been removed prior to the crash, though evidence suggested a late attempt to deploy the parachute.
Findings
- The aircraft was operating with incorrect propeller blades that were not designed for the aircraft's in-flight adjustment system.
- It is highly probable that a fuel cap became detached during flight and struck the pusher propeller, causing a portion of a propeller blade to break off.
- The resulting loss of thrust and intense vibrations likely forced the pilot to reduce engine RPM, further reducing power.
- The pilot's attempt to report wind issues to ATC may have diverted concentration away from managing the emergency.
- The aircraft's pusher configuration meant that any sudden power changes could contribute to a nose-down pitching tendency.
Safety action
- The manufacturer of the RANS S-12 was advised to issue a Service Bulletin requiring the installation of positive-lock fuel tank caps to prevent detachment.
- A recommendation was made to the Irish Aviation Authority to ensure that airport recording facilities remain operational during organized flying events like "fly-ins."