What happened
On August 13, 2007, at 13:38 UTC, an L 60 S aircraft, registration OK-NNH, operated by Aeroklub České republiky, attempted to tow a VSO-10 glider from runway 31 at the Hořice v Podkrkonoší airport (LKHC). During the initial takeoff roll, the glider's wing struck the ground, prompting the pilot to disconnect the towline after approximately ten meters. The towing aircraft continued its takeoff roll and became airborne after a very short run.
Following takeoff, the aircraft entered a steep climb during a right-hand turn, reaching an altitude of approximately 50 meters. During this maneuver, the aircraft lost airspeed and entered a right-hand spin. The aircraft struck the ground at a very steep angle, resulting in a post-crash fire. The pilot sustained fatal injuries.
The investigation
The ÚZPLN investigation focused on the aircraft's longitudinal trim settings and the pilot's pre-flight procedures. Investigators examined the trim mechanism and compared the measured distance of the trim chain to known values from a similar aircraft (OK-MTH). The investigation established that the trim was set to the extreme "tail heavy" position.
Testing on a comparable aircraft demonstrated that when the trim is set between the neutral and extreme "tail heavy" positions, the control forces required to operate the elevator become too heavy for a pilot to manage effectively during the takeoff phase. The investigation also noted that the pilot had only 5 hours of flight time on the L 60 S type, having performed only two previous towing flights earlier that month.
Findings
- The primary cause of the accident was the omission of a critical pre-flight task, specifically the failure to set the elevator trim to the neutral position.
- The aircraft was configured in an extreme "tail heavy" longitudinal trim setting, which caused an unusually short takeoff roll and a steep, unstable climb.
- The heavy control forces caused by the improper trim setting likely prevented the pilot from effectively managing the aircraft's pitch during the climb.
- The pilot failed to abort the takeoff after the initial difficulties during the takeoff roll.
- The aircraft entered a right-hand spin after losing airspeed during the climb, and the low altitude prevented successful recovery.
- The pilot's limited experience on the L 60 S type contributed to the inability to manage the developing emergency.