What aircraft was involved and where did it happen?

The accident on 2014-06-19 involved a WT-9 Dynamic, at LKPL, CZ.

What was the probable cause of the accident?

The accident was caused by a loss of control during a low-altitude approach, resulting from a partially open cockpit canopy that disrupted aerodynamic flow over the tail surfaces, compounded by turbulent air near the runway threshold.

WT-9 Dynamic crashes during approach at Plzeň-Letkov airport

A WT-9 Dynamic aircraft crashed during its final approach to runway 08 at LKPL, resulting in serious injuries to the pilot and the destruction of the aircraft.

What happened

On June 19, 2014, at approximately 16:47 UTC, a WT-9 Dynamic aircraft, registration OM-PPL, crashed while performing a landing approach at Plzeň-Letkov Airport (LKPL). The aircraft was engaged in glider towing operations, having recently released a glider approximately 2 km north of the aerodrome.

During the final stages of the approach to runway 08, the pilot was flying with extended flaps and the engine at or near idle power. To correct for being off-center and to manage altitude, the pilot executed a left slip maneuver. At an altitude of approximately 30 meters, the cockpit canopy partially opened. This event significantly disrupted the airflow over the tail surfaces, leading to a marked degradation in elevator control and an increased rate of descent of approximately 5 m/s. The aircraft's left wing struck a field of tall crops, causing the aircraft to impact the ground and flip onto its back. The pilot sustained serious injuries but was able to exit the wreckage independently.

The investigation

The ÚZPLN investigation utilized FlightTrack data, pilot testimony, and technical inspections of the aircraft. The investigation focused on the flight control systems and the canopy locking mechanism. Technical examinations confirmed that the canopy locking pin and the overall control systems were functional and that the design of the locking mechanism prevented accidental unlatching under normal conditions. The investigation also examined the meteorological conditions and the impact of local terrain features on the approach.

Findings

The primary cause of the accident was the aircraft's descent at a low altitude during approach, driven by several contributing factors.
The cockpit canopy was not fully secured prior to the maneuver.
The execution of a slip maneuver caused the unsecured canopy to partially open.
The partially open canopy disrupted the aerodynamic flow over the empennage, resulting in degraded elevator effectiveness and an increased sink rate.
The presence of turbulent airflow, likely caused by an earth berm located near the threshold of runway 08, likely disturbed the aircraft's approach path.
Due to the low altitude at which these events occurred, the pilot was unable to implement an effective recovery.