What happened
On July 27, 2023, a near-collision occurred at Slaglille Aerodrome (EKSL) involving two aircraft: a Schleicher ASK 21 (registration OY-XPL) and a Diamond HK-36R Super Dimona (registration OY-MXB).
The pilot of OY-XPL had just completed an aerobatic program in the nearby Slaglille Acro zone. Following the maneuvers, the pilot decided to perform a low-altitude pass across the threshold of runway 27, flying from north to south. The pilot of OY-XPL did not observe any aircraft on final approach and did not transmit any intentions over the radio.
Simultaneously, the pilot of OY-MXB was on final approach to runway 27. While the pilot of OY-MXB had previously noted aerobatic activity in the area, they did not expect a low-level crossing of the runway. As OY-XPL descended to an altitude of approximately 15–20 feet, the pilot of OY-MSB observed the glider diving toward them at high speed. The two aircraft passed over the runway threshold only about three seconds apart, with a vertical separation of roughly 10–15 meters. No injuries or aircraft damage were reported.
The investigation
The Danish Accident Investigation Board examined video footage of the event, FLARM data from OY-MXB, and radio communications. The investigation established that the Slaglille Radio frequency was unmanned at the time of the incident. While the pilot of OY-MXB had broadcast their position, the pilot of OY-XPL did not register these transmissions, partly due to cockpit noise experienced during the aerobatic maneuvers.
Investigators also looked into the decision-making process of the pilot in OY-XPL. It was noted that low-altitude crossings were a previously utilized practice by some local pilots, though no formal written procedures existed within the local gliding club's regulations for such maneuvers.
Findings
- The near-collision was caused by an impulsive decision by the pilot of OY-XPL to execute a low-altitude crossing across the active runway.
- The pilot's decision-making was likely influenced by a reduced level of focus following the physical strain of high-G aerobatic maneuvers.
- A sense of expectation pressure—a desire to demonstrate piloting skill, potentially exacerbated by the presence of a video camera—may have contributed to the risk-taking behavior.
- The pilot of OY-XPL failed to monitor radio communications effectively and did not announce the intended crossing.
- There was a discrepancy between established local club practices and standard safety procedures regarding low-level crossings.
Safety action
Following the incident, the local gliding club implemented several preventive measures, including:
- Requiring a ground-based traffic controller to monitor Slaglille Radio during aerobatic sessions.
- Mandating specific radio callouts at the start and completion of aerobatic programs.
- Implementing mandatory rest periods for instructors after a set number of aerobatic sessions.
- Improving coordination with local air traffic services to inform motorized aircraft of ongoing aerobatic activity.