Aviation safety investigations & reports

Partial power loss involving a Bell 47, VH-RTO, 9 km SE of Essendon Airport, Vic., 15 August 2013

Investigation number:
Status: Completed
Investigation completed


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On 15 August 2013, at about 1130 Eastern Standard Time, the pilot of a Bell 47G helicopter, registered VH-RTO, was returning to Essendon, Victoria. The pilot was instructed by air traffic control (ATC) to conduct one orbit due to traffic in the area. After completing the orbit, ATC further instructed the pilot to conduct a second orbit.

While maintaining 1,400 ft above mean sea level (AMSL), the second orbit was commenced. Shortly after, the helicopter began to vibrate severely, yaw from side to side in an oscillating motion, and the rotor revolutions per minute (RRPM) decreased. In response, the pilot lowered the collective in attempt to increase the RRPM, rolled on throttle, and manipulated the anti-torque pedals to counteract the yaw. However, the intensity of the vibrations increased and the oscillating yaw continued.

The pilot continued to manipulate the controls; however, as the helicopter was unable to maintain altitude and RRPM, he elected to conduct an autorotation. The pilot observed a park to his left and broadcast a ‘MAYDAY’ call.

With some power remaining, the helicopter landed in the park with nil injuries or damage sustained.

An engineering inspection identified that a spring in the distributor block of the left magneto was missing, which resulted in cross firing in the distributor and an associated loss of power.

A partial engine power loss presents a more complex situation to the pilot than a complete power loss. This incident highlights the importance of making timely decisions when a situation develops and the benefits of landing as soon as possible, before the situation deteriorates further.

Aviation Short Investigation Bulletin - Issue 24

Download Final Report
[Download  PDF: 215KB]
General details
Date: 15 August 2013   Investigation status: Completed  
Time: 1139 EST   Investigation level: Short - click for an explanation of investigation levels  
Location   (show map): 9 km SE of Essendon Airport    
State: Victoria   Occurrence type: Engine failure or malfunction  
Release date: 10 December 2013   Occurrence category: Serious Incident  
Report status: Final   Highest injury level: None  

Aircraft details

Aircraft details
Aircraft manufacturer Bell Helicopter Co  
Aircraft model 47  
Aircraft registration VH-RTO  
Serial number 25052  
Type of operation Private  
Sector Helicopter  
Damage to aircraft Nil  
Departure point Essendon, Vic  
Destination Essendon, Vic  
Last update 14 November 2018