What happened
On 16 July 2003, a Montgomerie-Bensen B8MR, registration G-BTFW, was conducting a private flight near North Coates, Lincolnshire. Prior to the flight, the pilot had performed maintenance on the aircraft, which involved draining and refilling the engine coolant with a new anti-freeze mixture.
Following a routine takeoff, the pilot observed that the engine coolant temperature had exceeded the standard operating range of 60 to 80°C. Suspecting an air-lock within the cooling system, the pilot reduced power and attempted an abbreviated circuit to return to the airfield. During the downwind leg of the flight, the engine lost power, causing the aircraft to descend. As the pilot attempted the final turn onto Runway 05, the rate of descent increased. The aircraft subsequently made a heavy landing into a cross-wind, which caused the helicopter to roll over.
There were no injuries to the pilot, though the aircraft sustained significant damage, including the destruction of the propeller and main rotor blades, as well as bent control rods, the rotor mast, and two support stays.
The investigation
The investigation was based on an accident report submitted by the pilot. An examination of the aircraft revealed that the bottom hose of the engine cooling system had detached from its connection at the radiator. The pilot noted that during the recent maintenance, his primary focus had been ensuring the hose would not chafe against the propeller gearbox, which led to the inadequate tightening of the jubilee clip securing the hose to the radiator.