Accident to the Sportine Aviacija Lak17 registered F-CHNF on 08/12/2022 at Salon-Eyguières

This is a courtesy translation by the BEA of the Final Report on the Safety Investigation. As accurate as the translation may be, the original text in French is the work of reference.

Note: the following information is principally based on statements. This information has not been independently validated by the BEA.

1. History of the flight

The pilot carried out a towed take-off from runway 33, with the flaps retracted and the trim set to a small nose-down attitude. He was the second pilot to carry out a towed take-off. The first pilot had reported strong, even severe crosswind turbulence on the radio during the climb. The wind (Mistral), from the north-north-east at 25 kt[1], was gusty, and the Alpilles hills, located north of the aerodrome, created strong turbulence at low height. After the end of the runway, the tug plane turned left to the west onto the  crosswind leg. At a height of approximately 165 m, during the climb, strong turbulence destabilized the glider. The towing cable lost its tension and came off the glider’s hook.

The tug pilot turned left onto the left-hand downwind leg to land on runway 33. The glider pilot announced on the radio that he was carrying out a reciprocal QFU landing on runway 15. He turned left onto a heading of 140° and joined the right-hand base leg. At the end of the turn onto final, he was at a height of approximately 150 m and at a distance of 2,100 m from the threshold. The glider then quickly lost height. The pilot extended the flaps to the second flap detent. He landed hard with the landing gear extended on a path covered with rocks, approximately 25 m before the runway 15 threshold. The glider made a ground loop during which the rear section of the fuselage broke and the landing gear collapsed. The glider came to a stop five meters before the runway. 

2. Additional information

2.1 Pilot’s experience

The 78-year-old pilot had owned the glider for three years. He held a glider pilot licence (SPL) issued in 2003. He indicated he had logged 2,200 glider flight hours of which 700 hours were on the LAK17 and 46 hours in the previous three months. He added that he had flown at Eyguières since 1989[2] and that he had carried out several hundreds of glider flight hours during the previous years.

2.2 Glider information

According to the manufacturer’s flight manual, the LAK17A glide ratio is 48. It has flaps with five positions that can be set, depending on the speed to: “L” (Landing), +2, +1, 0 and -1. With the flaps at +2, the glide ratio decreases to 42.

For the approach and landing, it is recommended to set the flaps to “L”, and, with light wind and when the ballast tanks are empty, the optimal approach airspeed is approximately 90 km/h. Stronger winds require a higher airspeed. It is recommended not to carry out an approach at too slow a speed with the brakes fully out, or the glider might drop during the flare.

According to the manufacturer’s flight manual, two tow hooks can be found on the LAK17. One near the main landing gear, to be used solely for winch take-off or auto-tow; and/or another one on the front part of the cockpit, next to the bulkhead and to be used solely for towed take-off with a tug plane. The pilot indicated that his glider only had one hook in front of the landing gear and that it had a back-up safety[3].

2.3 Statements

According to the witnesses who arrived on the site shortly after the accident, the speed brakes were retracted and locked. In the minutes after the accident, the pilot told them he had unlocked and slightly extended the speed brakes during the towing in order to make the cable taut again and remain in position behind the tug plane.

The runway assistant, who put the tow cable on the glider’s hook, indicated that he had tested it and that everything was normal.

The tug pilot (glider instructor and in charge of the operations on that day) explained that the air mass was laminar from 600 m up with a vertical speed of +7 to +8 m/s but that at around 300 m, there was rotors. After the accident he checked the cable and the hook and found no anomaly.

The pilot indicated that only two pilots wanted to take-off that day (including himself) and that they had had to collect the weather information by themselves. He had consulted the  https://meteo-parapente.com and Météo-France websites which forecasted a fairly strong wind. He explained that he was used to unstable air conditions but was surprised by the strength of the turbulence he encountered.

During the U-turn after the release of the cable, he thought that the glider’s descent rate was normal. Then the glider suddenly lost height on final when the wind was pushing it. He was stressed and focused on the vertical speed indicator which indicated – 5 m/s (needle to the stop) and kept sounding[4]. He did not remember visually checking the speed brake position. He could not think of anything else but getting back to the airfield on seeing the trees coming up. He did not exclude the possibility that the speed might have been low at the end because as he saw the trees coming up ahead of him, he might have reduced the rate of descent of the glider to pass over them. He did not look at the airspeed indicator again but thought he landed at 130 km/h. He added that he checked the speed brake position after the accident and said that they were retracted and locked.

2.4 Correction of vertical position with respect to tug plane and uncommanded cable release, during towed flight.

The Glider pilot manual[5] explains that if the cable loses its tension, the pilot must make it taut again by briefly extending the speed brakes.

If the cable unhooks or breaks during towing, the decision to be taken closely depends on the topography of the aerodrome and its immediate surroundings and on the height at which the incident happens.

• If it happens shortly after the take-off but there is enough runway length available, the pilot should land as soon as possible and brake.
• If it happens at a height over 80 m and if the wind allows it, the pilot should maintain the optimum approach speed and carry out a 180° turn and then a reciprocal runway landing.
• If it happens when it is no longer possible to reach the runway and when the glider is too low to attempt a U-turn, the pilot should carry out a forced landing in a field.

It is recommended that the pilot know the fields bordering the aerodrome and to have planned, at least once, a manoeuvre to land in one of them.

2.5 Measures taken by the gliding club

The pilots were reminded of the procedure to follow in case of unexpected release or rupture of the cable during towing (in accordance with the recommendations of the Glider pilot manual).

June 2023