What happened
On 8 June 2018, a Pierre Robin DR400/180R Remorqueur, registration G-LGCC, was performing a recovery to Dunstable Airfield after completing an aero-tow launch. While descending southbound at approximately 100 kt, the pilot's attention was momentarily diverted by an airliner approaching Luton Airport. Upon refocusing, the pilot identified a Schleicher ASK 21 glider, registration G-CFYF, at very close range directly ahead and slightly below.
In an attempt to avoid the aircraft, the pilot of G-LGCC performed a bunt maneuver to pass beneath the glider. However, the maneuver provided insufficient clearance, and the top of the tug's fin struck the outboard leading edge of the glider's right wing. The impact was severe enough to slice through the glider's structure and cause the top of the tug's fin and its rudder to detach. Despite the significant damage, both the no fatalities and no injuries were recorded as both aircraft remained controllable and were able to land safely.
The investigation
The investigation examined the flight paths of both aircraft, the visibility conditions, and the cockpit environments. It was established that the glider was tracking north-easterly at approximately 900 ft agl when the collision occurred. The crew of the glider had not seen the tug aircraft prior to the impact. The investigation also looked into the impact of the airfield's location within Class D airspace, which restricts maneuverability, and the effectiveness of various electronic collision avoidance systems like FLARM.
Findings
- The primary cause of the collision was that the pilots did not see each other's aircraft in sufficient time to take effective avoiding action.
- The pilot of the tug was distracted by observing an airliner on approach to Luton Airport.
- Environmental factors, including a slight haze and the sun's position, likely hindered the pilot's ability to spot the glider at a distance.
- Reflections in the glider's canopy compromised the instructor's ability to maintain an effective lookout.
- The high traffic density caused by restricted airspace at Dunstable increases the difficulty of maintaining visual separation.
Safety action
To mitigate the risk of future mid-air collisions, the gliding club implemented several measures:
- Enforcement of the policy to use landing lights on all aero-tow tugs during operations.
- Addressing radio interference issues caused by LED landing lights on tug aircraft.
- A review of the policy regarding FLARM fitment for club-owned aircraft.
- Investigating the installation of extended-life batteries to support better radio use and electronic conspicuity.