Background
The DHC-1 Chipmunk 22 (Lycoming), registration G-BCSB, was manufactured in 1952 and powered by a single Lycoming O-360-A4A piston engine. On 4 March 2000, the aircraft was engaged in private glider aero tows at a gliding club based at Royal Air Force (RAF) Cosford, Shropshire. The club is part of the RAF Gliding and Soaring Association (RAFGSA). At weekends, powered light aircraft use the single asphalt runway for basic flying training, while glider operations are confined to a parallel grass runway designated 24L, adjacent to the southern edge of the main runway. On such days, winch launching is prohibited and all glider flights commence with an aero tow.
History of the Flight
At approximately 0915 hrs, the pilot completed a daily inspection and pre-flight check of the aircraft. The first aero tow of the day occurred at 1100 hrs, flown by another pilot; it lasted about 15 minutes and was uneventful. The accident pilot then flew the Chipmunk for the next aero tow, commencing at 1158 hrs. After towing a glider to 5,000 feet and releasing, the Chipmunk landed and taxied to tow a single-seat glider. The glider pilot requested a tow to 3,000 feet, which was acknowledged. The glider was attached, the Chipmunk moved forward to take up slack, and ATC granted take-off clearance. Witnesses noted normal acceleration along the left side of the grass runway.
The glider became airborne slightly before the Chipmunk, settling at an estimated 6 to 10 feet. Two witnesses observed from the northern side of the asphalt runway, about 500 metres away. They noted that, after becoming airborne, the glider briefly contacted the ground and bounced back into the air. One witness believed this caused the Chipmunk to pitch nose down before rising to a high nose attitude of approximately 5 to 10°. The Chipmunk was then airborne at heights between 6 and 20 feet and began a slow, steady left turn to a maximum bank angle of about 5°. The glider pilot, sensing something amiss, released the glider, turned right, and landed straight ahead 625 metres from the start. The Chipmunk continued turning left; its nose rose steeply before the left wing struck a telegraph pole. The wing detached, and the aircraft rolled, descended, and struck the ground inverted. A witness who saw only events after glider separation believed the Chipmunk was still on the ground while veering left, becoming airborne just before the pole. The pole was struck at an estimated height of 25 feet. Two witnesses instructed a colleague to inform ATC and drove to the site with a crash vehicle. Foam was sprayed on leaking fuel to inhibit fire. The airfield fire and rescue services arrived, followed by the air ambulance at 1240 hrs. Although the pilot had received only minor injuries in the impact, he was found dead, having suffered a heart attack.
Operating Area and Conditions
Runway 24/06 at RAF Cosford is 1,149 metres long with asphalt. The grass Runway 24L, approximately 1,100 metres long and level, was in use. The grass was short and the surface firm and dry. Normal practice was to use the side farthest from the main runway. To the left of Runway 24L, an area of longer grass and weeds extended along the first 400 metres, restricting runway width to about 50 metres. Beyond this scrub, there was flat grass leading to the airfield boundary. A windsock was located 380 metres from the start, 30 metres left of the runway edge, near a 30-foot high telegraph pole. The windsock, fully deployed leftward under prevailing wind, was visible; its supporting pole was painted white. To the left were trees up to 30 feet high with sparse foliage, surrounded by bushes, and touring caravans. The struck telegraph pole was not easily visible against this background.
Take-off Performance
Post-accident tests by the RAFGSA measured take-off distance for a similar tug-glider combination. Three take-offs under broadly similar conditions showed an average ground run of 160 metres, with less than 10 metres variation.
Meteorological Conditions
Local conditions recorded hourly from 0850 hrs showed surface wind from the northwest, increasing from 8 kt to 15 kt. Visibility was generally more than 20 km with occasional light snow showers. Cloud was scattered at 2,500 feet and broken at 21,000 feet. A special observation at 1238 hrs recorded surface wind 310°/15 kt, visibility 26 km, few clouds at 2,000 feet, broken at 3,000 feet, temperature +6°C, dew point +2°C. These conditions were benign for glider towing. The crosswind from the right was calculated at 14 kt; the published crosswind limit was 15 kt.
Pilot Experience and Medical History
The pilot held a valid Private Pilot's Licence issued in 1987. He was an experienced glider pilot and qualified gliding instructor, serving as the club's 'Tug Master'. He had completed 1,288 aero tows in the Chipmunk and had been a club member for 15 years. His last medical examination on 28 August 1999 found no abnormalities. In 1995 his blood pressure was raised but not considered significant; no treatment was prescribed. At the time of the accident he was not receiving medical treatment. On the evening prior, after heavy gardening, he looked pale and complained of tiredness. He made no complaints of illness on the morning of the accident.
Pathological Findings
Post mortem examination revealed evidence of a myocardial infarction (heart attack). The pathological evidence suggests the sequence was initiated by this infarction, which probably occurred in the early morning of the accident day. Although not fatal at that time, it is believed the infarction extended while the pilot was initiating his second take-off, causing incapacitation. This led to deviation left and the crash. The pilot utilized the full shoulder harness and suffered only minor injuries from impact. No alcohol or drugs were found; carbon monoxide saturation was 1%, within normal range.
Aircraft Handling Characteristics
The Chipmunk, fitted with a Lycoming engine, has a propeller that rotates clockwise (as viewed from the cockpit), causing a tendency to yaw left during take-off until wings lift the main wheels. This yaw tendency would have been reduced slightly because the aircraft would naturally turn into the prevailing wind (to the right). However, with full engine power, slipstream over the rudder would provide adequate control authority to maintain direction.
Ground Marks
Two parallel tyre tracks were found in the area of scrub on the left side of Runway 24L.