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The pilot of a BK117 helicopter reported that while in a gentle climb at about 4,600 feet during a post maintenance test flight, the helicopter suddenly pitched nose-up. The indicated airspeed decreased to zero and the helicopter then pitched nose-down to a slightly inverted attitude. After descending about 2,000 feet, the pilot regained control and landed safely.

Inspection of the helicopter systems by the company maintenance personnel could not find any reason for the sudden loss of control.

A Bureau of Meteorology area forecast, issued on the day of the incident, indicated severe turbulence below 10,000 feet. The forecast also included increasing westerly wind speeds ranging from 30 knots at 2,000 feet to 45 knots at 10,000 feet. The actual weather report for the area that the helicopter was operating in, indicated westerly wind speeds increasing from 35 knots at 2,000 feet to 50 knots at 7,000 feet. These conditions are conducive to mountain wave and rotor activity.

A rotor is a large air mass rotating about a substantially horizontal axis. It is generated in the lee of a mountain or sharp ridge in strong wind conditions.

The helicopter was operating on the lee side of a mountain range when the pilot experienced the rapid loss of control. It is probable that the helicopter encountered a rotor.

 
General details
Date: 17 July 2000 Investigation status: Completed 
Time: 1430 hours EST Investigation type: Occurrence Investigation 
Location   (show map):9 km E Warragamba Dam, (VTC Check Point) Occurrence type:Loss of control 
State: New South Wales Occurrence class: Operational 
Release date: 03 May 2001 Occurrence category: Accident 
Report status: Final Highest injury level: None 
 
Aircraft details
Aircraft manufacturer: Messerschmitt-Bolkow-Blohm 
Aircraft model: BK117 
Aircraft registration: VH-BKZ 
Serial number: 7213 
Type of operation: Aerial Work 
Damage to aircraft: Substantial 
Departure point:Bankstown, NSW
Departure time:1345 hours EST
Destination:Bankstown, NSW
Crew details
RoleClass of licenceHours on typeHours total
Pilot-in-CommandCommercial346.05080
 
 
 
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Last update 13 May 2014