What happened
On 8 September 2019, a Hurricane 3 15, registration G-OHUR, was conducting flight tests near Stoke Airfield, Kent. The pilot was performing a series of maneuvers to determine the ideal propeller pitch setting. After successfully completing a circuit at a 9° pitch, the pilot adjusted the setting to 6° and performed engine power and magneto checks.
During the subsequent takeoff, the engine reached 5,600 rpm, but at an altitude of approximately 50 ft, the engine began to vibrate significantly and the engine note changed. Adjusting the throttle did not mitigate the vibration. While attempting to avoid nearby marinas and paddocks, the pilot noted a loss of power and a decaying airspeed, signaling an imminent stall. To avoid a more dangerous situation, the pilot executed a forced landing on the salt marshes adjacent to the River Medway.
Upon contact with the ground, the main landing gear dug into the earth, causing the aircraft to pitch forward and come to rest in an inverted position. The pilot was briefly trapped due to a distorted canopy but was helped from the cockpit by a bystander. There were no injuries to the pilot.
The investigation
The investigation focused on the mechanical state of the engine and the cause of the sudden vibration. As a Single Seat Deregulated Aircraft (SSDR), the aircraft was a private build. The pilot examined the Rotax 503 DCDI engine following the event. While no specific component failures were identified in the engine or the reduction gearbox, investigators noted an unusual amount of oil residue beneath both pistons in the crankcase.
Although one spark plug was found to be wet with fuel, the overall condition of the spark plugs suggested the engine had been operating with the correct mixture prior to the incident. The propeller blades remained set at the 6° angle used during the flight, despite the propeller detaching during the impact.
Findings
- The aircraft sustained damage to the fuselage, left wing, and landing gear, and the propeller became detached.
- The engine experienced a sudden onset of heavy vibration and a subsequent loss of power.
- Carburettor flooding is considered the most likely cause of the engine's rough running and vibration, although the specific trigger for the flooding could not be confirmed.