Engine cooling fan fracture - VH-IDU, Rolleston, Queensland, on 3 May 2009

On 3 May 2009 at approximately 0620 Eastern Standard Time, a Bell Helicopter Company model 47G-2A-1 helicopter departed Rolleston aircraft landing area, Queensland, on a private flight. At an altitude of approximately 200 ft above ground level during the climbout, the pilot reported hearing a very loud bang and feeling a jolt through the airframe. The helicopter immediately started descending and the pilot noted that the forward/aft cyclic control was unresponsive. The helicopter subsequently landed heavily, resulting in the main rotor blades severing the tail boom and causing some structural damage to the airframe. The pilot reported suffering a minor back injury as a result of the heavy landing.

The Australian Transport Safety Bureau's (ATSB) examination of the helicopter revealed that two blades had separated from the engine cooling fan as a result of fatigue fracture. The fan cowling had fractured and separated from the engine and there was impact damage to the flight control linkages.

The ATSB examination determined that the fan unit had not been correctly assembled in accordance the Bell 47 aircraft maintenance manual, and that this probably had an effect on the vibration and resonance characteristics of the fan, which in turn may have increased the susceptibility of the fan to fatigue failure.

As a result of this occurrence, the Civil Aviation Safety Authority released Airworthiness Bulletin AWB 63-007, reminding operators and maintainers of the importance of adhering to all current manufacturer's approved data for sheet metal cooling fans and their drive assemblies.