What happened
On April 20, 2016, at approximately 15:50 UTC, an L 200D aircraft, registration OK-RMA, was performing a visual flight rules (VFR) flight originating from Panenský Týnec (LKPC). After performing several 360-degree turns near Litoměřice at approximately 2,000 ft AMSL, the pilot attempted to conduct a low-level reconnaissance flight of the non-public landing area at Litoměřice (LKLMER) to practice approach procedures.
While flying along the Labe River, the aircraft descended to an altitude of approximately 30 m AGL. During this low-level maneuver, the aircraft in a slight right bank struck the upper phase conductors of a 2x22 kV overhead power line. The impact caused the wires to snap and fall into the river, triggering phase protections and a subsequent power outage in the local distribution system. The pilot, unaware of the strike at the moment of impact, continued the flight and landed safely at LKPC, where the damage to the right propeller and fuselage was discovered.
The investigation
The ÚZPLN investigation examined the aircraft's flight path, the physical evidence at the site, and witness testimonies. Investigators recovered blue paint traces from the aircraft's propeller and fuselage that matched the coating on the broken power lines. Radar analysis confirmed the aircraft's presence in the area, though the lack of an SSR transponder on the aircraft prevented precise altitude reconstruction. Witnesses near the river reported seeing the aircraft tilt to the right and strike the wires, followed by loud bangs and visible electrical arcing.
Findings
- The pilot was flying at an altitude of approximately 30 m AGL, which is significantly below the minimum permitted altitude of 150 m (500 ft) AGL for non-essential flight operations.
- The descending below the minimum allowable altitude into a flight path that was in collision with the overhead power lines was the primary cause of the incident.
- The overhead power lines were not marked with aviation warning spheres, as they did not meet the specific criteria for mandatory marking under current regulations.
- The aircraft was not equipped with an SSR transponder, which hindered the ability to precisely determine the exact altitude during the collision.
- While the pilot was unaware of the specific location of the wires, the transmission towers significantly exceeded the height of surrounding vegetation, suggesting the hazard could have been identified.