Glaser-Dirks DG-100 glider, G-DDFN, 4 August 2012

21� Crown copyright 2013 AAIB Bulletin: 7/2013 G-DDFN EW/C2012/08/01 ACCIDENT Aircraft Type and Registration: Glaser-Dirks DG-100 glider, G-DDFN No & Type of Engines: None Year of Manufacture: 1975 (Serial no: 30) Date & Time (UTC): 4 August 2012 at 1131 hrs Location: Pluckerston Farm, Kirriemuir, Angus Type of Flight: Private Persons on Board: Crew - 1 Passengers - None Injuries: Crew - 1 (Fatal) Passengers - N/A Nature of Damage: Aircraft destroyed Commander’s Licence: Bronze gliding certificate Commander’s Age: 59 years Commander’s Flying Experience: 28 hours (of which 5 were on type) Last 90 days - 2 hours Last 28 days - 1 hour Information Source: AAIB Field Investigation Synopsis Whilst turning to the right, the glider was seen to enter a spin from which it recovered after about two turns. The glider was seen to fly normally for about a minute and it then entered a second spin, from which it did not recover. The pilot was fatally injured. History of the flight The pilot had joined the gliding club at Drumshade in April 2010 and followed a structured period of training, gaining his Bronze gliding certificate in July 2011. He purchased G-DDFN in August 2011 and kept it, rigged, in a hangar at the gliding site. On the day of the accident, the pilot was the first to arrive at the gliding site and was seen by another member at about 0900 hrs, working on the club tractor. He was intending to carry out a 100 km cross-country flight, which included a 50 km leg, as part of a requirement for a Silver gliding cerificate. Club members assisted him to move his glider to the launch point, where he carried out the daily inspection and control checks. The airbrake stowage boxes in the wings had a significant amount of water in them due to recent rain, which was removed using a sponge and the boxes dried. The weather was good, with visibility in excess of 10 km and cloud generally ‘broken’ at 1,500 to 3,000 ft, with some showers forecast. At the time of the accident the visibility was good and the cloud base above 2,500 ft. 22� Crown copyright 2013 AAIB Bulletin: 7/2013 G-DDFN EW/C2012/08/01 At about 1115 hrs the glider was positioned for a winch launch on the easterly runway. The launch appeared normal, with the glider releasing at the top of the climb. Club members did not continue to watch the glider but concentrated on preparing the other gliders for flight. Recorded information was available from an electronic flight logger recovered from the aircraft. The recorder contained a track log of the entire accident flight, with GPS-derived position, groundspeed, altitude and pressure altitude. The data is illustrated in Figure 1, showing the track over the ground. The launch and subsequent manoeuvres including the accident were observed by a witness who was at the eastern end of the strip. He saw the glider flying in right‑hand orbits to the northeast before appearing to enter a steep nose-down spin. The glider recovered after what he estimated to be about two turns and headed away from the field, to the north, before making another orbit to the right. The witness described the orbits as having a “gentle bank angle”. The glider then appeared to enter another spin, from which it did not recover, and was seen to impact the surface of a crop field. The witness alerted the club members to the accident and they contacted the emergency services before attending the scene. The pilot had been fatally injured in the impact. Figure 1 G-DDFN – Flight recorder GPS track 23� Crown copyright 2013 AAIB Bulletin: 7/2013 G-DDFN EW/C2012/08/01 Medical and pathological information A post-mortem examination was carried out by a forensic pathologist. The pathologist established that the pilot had died as the result of injuries received in the accident, which the pathologist considered non-survivable. While there was some evidence of hypertensive heart disease, which could have produced an incapacitating episode, the circumstances of the accident, including the aircraft recovering from one spin, suggested this was unlikely to have been a factor. The toxicological analysis confirmed the presence of the pilot’s prescription medication and there was no evidence of other drugs or alcohol. Video of previous flights The pilot had been in the habit of wearing a head‑m of the accident flight but on-board video recordings of five previous flights were on the memory card. These showed that the pilot, when orbiting to the left or right to gain height in thermals, maintained his airspeed between about 40 kt to 45 kt and used approximately 30° angle of bank. Entry into a turn was typically smooth with some adverse yaw initially 1 but when established in the turn it was correctly balanced with rudder. Flight Handbook for DG-100 The Flight Handbook does not promulgate a stalling speed but an independent flight test document stated: ‘Level flight stall occurred at about 36 kts. Very little buffeting preceded the stall.’ Footnote 1 The tendency for the aircraft to yaw in the opposite direction to the turn. Deliberate spin entry and the procedure for spin recovery are set out in the Flight Handbook: ‘1. Spins: Entry: Start a slow pull-up. When the aircraft starts to buffet apply full back stick with rudder in the desired direction of rotation. Recovery: Rudder in the direction opposite to rotation, pause, then ease the stick forward. When rotation stops, neutralize rudder and gently recover from dive.’ From discussion with pilots who had flown the DG‑100, its handling qualities were described as benign and docile. Recorded information Introduction As noted above, recorded information was available from a flight recorder 2 recovered from the aircraft. The recorder contained a track log of the entire accident flight, with GPS-derived position, groundspeed, altitude and pressure altitude recorded once every two seconds. A portable data assistant device 3 (PDA) operating a navigation application 4 was also recovered. The pilot had entered a triangular route of approximately 63 nm (116 km) into the PDA, with the first leg to Alyth, second leg to Fordoun and return leg to Drumshade. The data is illustrated in Figure 1, showing the track over the ground, and Figures 2 and 3, showing time-history plots of track, groundspeed and altitude parameters. Footnote 2 EW Gliding Commission (IGC). 3 Hewlett from the EW manufactured microRecorder. 4 XCSoar 24� Crown copyright 2013 AAIB Bulletin: 7/2013 G-DDFN EW/C2012/08/01 Figure 2 G-DDFN –Altitude, track and groundspeed (Takeoff to ground impact) 25� Crown copyright 2013 AAIB Bulletin: 7/2013 G-DDFN EW/C2012/08/01 Figure 3 G-DDFN – altitude with track, groundspeed and bank angle (calculated) (Final minutes of flight) 26� Crown copyright 2013 AAIB Bulletin: 7/2013 G-DDFN EW/C2012/08/01 Interpretation The track log commenced at 1119:35 hrs, with the glider at the threshold of the easterly grass runway. The glider was then launched to an altitude of 1,080 ft (about 850 ft gl) in Figures 1 and 2). Having descended, after launch, to an altitude of about 825 ft (600 ft agl), the pilot then flew a continuous series of clockwise thermalling turns, climbing at an average rate of 150 ft/min, carried to the west by the wind. Analysis of this period of thermalling flight indicated an average bank angle 5 of about 21° and an average airspeed of about 39 kt. At 1129:05 hrs the glider was at ‘Point B’, about 220 m to the east of the airfield’s western boundary at an altitude of 1,640 ft (1,400 ft agl). It then flew north, still climbing and made a turn to the right; at ‘Point C’ the aircraft reached its maximum altitude of 1,750 ft (1,540 ft agl), with airspeed calculated as about 36 kt, and a bank angle of about 18°. The glider then started to descend rapidly, reaching a rate of about 4,000 ft/min (~66 ft/sec). After six seconds, and at an altitude of 1,180 ft (970 ft agl), the descent was arrested and the glider recovered to about 1

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Glaser-Dirks DG-100 glider, G-DDFN, 4 August 2012

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