Aviation safety investigations & reports

Bell 47G-3B1, VH-KSL, 20 km E Narbarlec NT, 10 July 1988

Investigation number:
Status: Completed
Investigation completed


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The pilot had shut down the helicopter to kill and load meat for a stock camp. After starting and completing the after-start checks, the pilot first entered a low hover. The aircraft was then put into a high hover about 10 ft above the tree tops before a climb was initiated into a wind of 15-20 kts. The pilot reported that as he accelerated through about 40 kts, he noticed a substantial reduction in the manifold pressure reading with the engine RPM at about 3000. The aircraft then began to sink into the tree tops. Some 100 metres further on, the main rotor blades struck a large tree trunk and the aircraft fell to the ground on its right side. The pilot was rendered unconscious at impact, but after regaining consciousness he assisted the surviving passenger from the wreckage and freed the other passenger's leg from under the cabin before dragging him clear. A strip inspection of the engine and turbocharger revealed significant defects. These included the density controller was set below tolerance; a cracked and warped wastegate butterfly; and a sticking wastegate actuator. Physical damage to the engine was attributed to poor engine handling. The cumulative effects of these defects would have reduced the available power output from the engine, but do not in themselves explain the symptoms reported by the pilot. In addition, the power available was sufficient for the pilot to execute a towering take-off. A turbocharger failure would have produced the loss of power experienced by the pilot, but no possible cause or result of such a failure was discovered. The pilot reportedly did not make a significant reduction in power after the high hover, so that it is unlikely that a sticking wastegate caused the problem. The cause of the reported loss of power was not determined.

Download Final Report
[Download  PDF: 23KB]
General details
Date: 10 July 1988   Investigation status: Completed  
Time: 1752    
Location: 20 km E Narbarlec    
State: Northern Territory    
Release date: 20 December 1988   Occurrence category: Accident  
Report status: Final   Highest injury level: Fatal  

Aircraft details

Aircraft details
Aircraft manufacturer Bell Helicopter Co  
Aircraft model 47  
Aircraft registration VH-KSL  
Serial number 6642  
Type of operation Business  
Sector Helicopter  
Damage to aircraft Substantial  
Departure point Goomadeer Mission NT  
Departure time 1750  
Destination Goomadeer Mission NT