Incident Overview
On 4 August 2012 at 1330 UTC, a privately operated Hiller UH-12 B helicopter, registration N38763, was involved in an accident at Elstree Aerodrome in Hertfordshire. The helicopter was manufactured in 1953 (serial number 497) and powered by a single Franklin 6V4-200-C33 piston engine. The flight was a private visual circuit with one pilot and one passenger on board. The commander, aged 70, held an Airline Transport Pilot's Licence and had accumulated 2,400 total flying hours, of which 57 were on type. Weather conditions were fine with a surface wind from the south-west at 15 knots and an air temperature of 15°C.
Sequence of Events
The pilot had conducted hovering practice on the airfield for approximately 15 minutes before transitioning to a visual circuit. While on the downwind leg, the pilot noticed a high engine oil temperature and low oil pressure, both of which had been normal during the earlier hover. The pilot immediately turned towards a grass area north of the runway for an emergency landing. As the helicopter lost translational lift, the pilot observed main rotor rpm decreasing and applied power to correct. However, rotor rpm did not recover, leading the pilot to lower the collective control. The helicopter descended in a slightly tail-low attitude, and the tail struck the ground.
Damage and Injuries
The accident resulted in damage to the tail rotor assembly, tail rotor gearbox, and tail boom. Neither the pilot nor the passenger sustained any injuries.
Pilot's Assessment
According to the pilot's report, the helicopter experienced a loss of power. The pilot further assessed that this situation was compounded by the carburettor heat control not having been returned to the 'cold' position before the approach and landing.