Incident Narrative
On April 16, 2016, at 8:58 UTC, a glider pilot launched via winch in a SZD-41A Jantar Std. glider for a thermal flight in the vicinity of the airport (CTR EPLL). After launch, the pilot encountered thermal lift. Approximately fifteen minutes into the flight, due to a wind direction of 180°, the pilot requested and received permission from TWR at 9:17 UTC to transition to the north side of the airport for 10 minutes.
At 9:24 UTC, radio contact with the glider was lost. The TWR controller attempted to re-establish communication on the tower frequency without success. The regional aeroclub instructor supervising glider flights that day also made attempts. The glider's position was visually identified and reported to TWR. Further efforts included telephone calls to the pilot, use of a signal pistol, and display of landing signals on the grass runway, all without response.
Continuous visual contact was maintained from the tower; the glider was the only aircraft airborne at that time, located northeast of the airport. To ensure geographic separation, a scheduled flight (RYR87FK, B738) departed westward at 9:39 UTC.
At 9:43 UTC, the pilot increased the radio volume and established communication with TWR, reporting a transition to the south side of the airport. Upon regaining contact, the supervising instructor ordered an immediate landing. The pilot complied and landed at 9:53 UTC. No further communication issues occurred. Post-landing radio checks revealed no faults.
During a telephone conversation after the incident, the pilot explained that he had not heard the calls; the radio was tuned to the TWR frequency but he believed he could continue flying while north of the airport, and later contacted TWR to report the transition.
The pilot held a valid glider license and medical certificate, with recent flight experience. In the 14 days prior, he had flown 4 flights totaling 44 minutes, including 3 flights (36 minutes) in the same glider without communication issues. The glider had accumulated 5 hours 21 minutes in the current season with no reported defects.
Probable Cause
The investigation determined the cause was lack of monitoring of radio communication in CTR EPLL (excessive quieting of the radio) and insufficient observation of the airport, caused by the pilot's concentration on thermal flight.
Preventive Actions
The glider operator decided to remind pilots before flights about the need for continuous radio monitoring, strict adherence to granted clearances, and observation of airport traffic.