What happened
On 4 August 2012, a Hiller UH-12 B, registration N38763, was conducting private flight operations at Elstree Aerodrome. The pilot was performing hovering practice on the airfield approximately 15 minutes before intending to transition into a visual circuit. During the hover, the pilot observed a high engine oil temperature and low oil pressure, despite these parameters having been normal earlier in the flight.
In response to these readings, the pilot steered the aircraft toward a grass area north of the runway to perform an immediate landing. As the helicopter began to lose translational lift, the pilot noted a reduction in main rotor RPM. An attempt to apply power to stabilize the aircraft was unsuccessful, and as the RPM continued to drop, the pilot lowered the collective control. This resulted in the helicopter descending in a slight tail-low attitude, causing the tail to strike the ground. The impact caused damage to the tail rotor, the tail rotor gearbox, and the tail boom.
The investigation
The investigation examined the engine parameters and the pilot's configuration of the aircraft's systems. It was established that while the engine oil temperature and pressure had fluctuated, the pilot's assessment of a power loss was accurate. The investigation also looked into the settings of the engine's heating controls during the approach and landing phase.