Introduction
On 6 July 2004 at approximately 1154 UTC, a Robinson R22 Beta helicopter (registration G-LIDS) and a Hybred 44XLR microlight (registration G-MTJP) collided mid-air at about 1,200 feet overhead Welham Green, Hertfordshire. The helicopter was conducting a training flight under visual flight rules (VFR) in good visual meteorological conditions (VMC). The microlight was on a private flight returning from Hunsdon to Plaistow Farm near St Albans.
History of the Flight
Background
The microlight pilot and his passenger departed Plaistow Farm at about 1000 hrs and arrived at Hunsdon at about 1100 hrs. After a short stop, they departed Hunsdon at about 1130 hrs, climbing to circuit height before heading south. The helicopter instructor, who held an Airline Transport Pilot's Licence and had 13,940 total flying hours (580 on type), arrived at Elstree Aerodrome at about 0930 hrs. He met his student at 1015 hrs for a trial lesson consisting of a one-hour ground briefing and a one-hour flight. The flight was conducted with the student in the right seat. After engine start, the instructor booked out and departed Elstree at 1114 hrs to the north-west, climbing to 1,000 feet. During the next 40 minutes, the instructor demonstrated exercises including turns, speed changes, climbs, and descents.
The Collision
Both aircraft were operating at about 1,200 feet QNH. Radar data from Stansted showed the microlight tracking approximately 245° true at a ground speed of 65 kt. Witnesses saw the microlight holding a constant heading and level attitude. The helicopter had just completed a high hover at 1,800–2,000 feet and transitioned into forward flight. To demonstrate the effect of increasing airspeed on rotor RPM, the instructor turned right onto a track of 100° true and switched off the engine governor. He descended slightly, increasing airspeed from 55 to 85 KIAS. After levelling at about 1,200 feet, the student, looking left, noticed the microlight in his right peripheral vision. Simultaneously, the instructor saw the microlight through the left front transparency, slightly below and filling approximately 60% of his windscreen. Perceiving it moving left to right, he applied full left cyclic, but the aircraft collided.
Aftermath
The helicopter pitched nose down, the instructor felt an impact to his left foot, and the windshield disintegrated. The instructor transmitted a MAYDAY call to Elstree, reversed his left turn, and entered autorotation. He landed safely in a crop field. The student was uninjured. The microlight suffered severe structural damage, descended out of control into a wooded area, and both occupants were fatally injured.
Engineering Information
Accident Site Details
The microlight struck the ground nose-first at the base of trees, bringing down light branches. The trike separated from its wing due to failure of the mono-pole structural member. Debris from the helicopter—fragments of transparency and door frame—and three pieces of microlight wing tubing were scattered east of the collision site. The outermost portion of the right wing, about 1 metre long, was found lodged in tree branches approximately 100 metres east of the main wreckage. Pieces of wooden propeller blade were found at the western extremity; one had fibres from the sailcloth-covered wing. The helicopter landed about 1 km east of the collision area.
Detailed Examination
Helicopter: The left side of the cockpit transparency was missing, along with the left door except a small frame section. The chin area of the fuselage was distorted and imprinted with dark purple dye from the microlight sailcloth. Impact damage extended from the nose landing light bezel around to the left door cut-out, centred at the 10 o'clock position. The mid-section of the front doorframe was deflected rearwards, limiting left yaw pedal travel—this accounted for the instructor's foot injury. Main rotor blades had minor damage near the tips, with leading-edge distortion on one blade and a chord-wise smear approximately 1 metre inboard. Fibres from the microlight wing fabric were found on a blade tip.
Microlight: All damage to the trike occurred during tree and ground impacts. The mid-air collision involved only the wing upper surface. An inboard left wing leading-edge tube, about 1.4 metres long, had broken off and exhibited bending overload failures at each end. An indentation in the tube about 0.5 metres from the nose was probably made by a helicopter skid during the collision. The wing fabric had sustained a chord-wise cut consistent with helicopter main rotor blade contact. No evidence of pre-existing defects was found.