Summary
On 16 September 2005, a Robinson R44 Astro, registration G-TATY, crashed near Amersham, Buckinghamshire during a solo cross-country training flight. The student pilot sustained serious injuries. The helicopter was severely damaged. Investigation found no technical fault; rotor blade rotational speed was below power-on limits at impact.
History of the Flight
The student pilot and an instructor had completed ten minutes of circuits at Denham Airfield. The instructor then disembarked with rotors running and authorized the student for his first solo navigation exercise. The planned route was from Denham northwest to Westcott disused airfield and back, a distance of 23 nm. The pilot annotated his chart with a heading of 312° (M) and a time of 14 minutes, indicating a groundspeed of 100 kt. G-TATY took off from Runway 06 at 0849 hrs and turned left for a standard departure via the Maple Cross NDB. The flight information service officer observed no anomalies. The helicopter then turned further left towards Westcott, heading in the direction of Amersham. About five minutes after takeoff, it was seen flying at low height south of Amersham. Seven witnesses observed the helicopter perform energetic maneuvers before it struck the ground in a nose-down attitude and came to rest upright. The pilot was removed from the helicopter by emergency services, conscious, and airlifted to hospital.
Witness Accounts
Seven members of the public witnessed the accident. One witness, walking her dogs, became aware of a noisy helicopter approaching from the east at low height. She noted the main rotor blades appeared to turn more slowly than normal. The helicopter flew past, turned left, pitched nose down, and swung through 360°. It then flew away up a sloping field, seeming to recover energy, before she lost sight. She then heard a crash and called emergency services at 0855:29. She approached the helicopter and found the pilot with a visible throat injury, unable to speak, and trying to release his seatbelt. She assisted him until emergency services arrived. Six other witnesses heard unusual engine noises described as two loud choking sounds, a dull pop, or phuts. Two stated the engine sounded as if it was going to cut out, with oscillations. Two witnesses saw a steeply banked left turn, and all agreed the helicopter adopted a very steep nose-down attitude, descended rapidly, briefly leveled, then pitched nose down again and turned right. One witness saw G-TATY strike the ground nose first and fall back to an upright attitude. The aircraft came to rest a few meters from the northern edge of Rodger's Wood. No fire occurred.
Pilot Information
The 59-year-old pilot held a Private Pilot’s Licence for aeroplanes (obtained January 2002) and a student pilot certificate for helicopters. He had 224 total flying hours, of which 31 were on helicopters, including 2 hours 30 minutes solo. The accident occurred on his first solo cross-country flight. Due to head injuries sustained in the accident, he could not recall the flight. A cognitive interview did not yield additional information. His primary instructor described him as a slow learner who handled the helicopter well with the cyclic trim on, but had a tendency to treat it like a fixed-wing aircraft. He was good at controlling rotor rpm with the governor off and at autorotations, but hovering was not a strong point. He was sometimes slow to react and occasionally overrode the governor by gripping the twist-grip throttle too tightly. He received little instruction on downwind landings and was unfamiliar with the increased power required during transitions through zero airspeed and the potential for vortex-ring state. His radiotelephony skills were not considered good.
Aircraft Information
The Robinson R44 Astro is a four-seat single-engine helicopter with a maximum gross weight of 1,089 kg. The primary fuselage is constructed of welded steel tubing covered with riveted aluminum skin, with skid landing gear. It is powered by a Lycoming O-540-F1B5 piston engine with a carburetor and carburetor heat system. Engine power is transmitted via belts to the main rotor and tail rotor driveshafts. Flying controls are mechanical without hydraulic assistance; the cyclic has an automatic electric trim system. The helicopter is equipped with a carburetor heat assist device that correlates heat application with collective setting. G-TATY was manufactured in July 1999 and had accumulated 421.2 hours at the time of the accident. Its last STAR annual inspection was completed on 6 September 2005 at 418.9 hours, with no recorded defects.
Meteorological Conditions
The weather was reported as fine, but the surface wind at the time of the accident exceeded both the manufacturer's and operator's limitations. A meteorological aftercast described high pressure over the central Atlantic.
Probable Cause
The evidence indicated that the rotational speed of the rotor blades was below the 'power on' limits at the moment G-TATY struck the ground.