The Transport Accident Investigation Commission in New Zealand yesterday added two new significant items to its Watchlist of most pressing concerns. One involves Robinson helicopter and the other safety issues for pedestrians and vehicles using railway level crossings. The detail provided on Robinson helicopters is as follows:-
There are around 300 Robinson helicopters registered in New Zealand comprising around 40% of the total helicopter fleet.
Since 1996, the Commission and the Civil Aviation Authority (CAA) have investigated 14 “mast bumping” accidents involving Robinson helicopters, costing the lives of 18 people.
Mast bump is contact between an inner part of a main rotor blade or a rotor hub and the main rotor drive shaft or “mast”. The outcome is usually catastrophic.
“We understand what mast bumping is, but it is often difficult to determine exactly what happened to cause the mast bump,” said Commissioner and spokesperson Stephen Davies Howard.
“We know the condition results when Low-G occurs – a bit like when you leave your stomach behind when going over a hump on a country road – or from an inappropriate control input. Low-G can be caused by turbulence, but it is not normally a condition that causes concern beyond discomfort,” said Commissioner Davies Howard.
“However, it can lead to mast bumping which too often has fatal consequences in Robinson helicopters with their rotor head design.”
The Commission had also identified that the rate of Robinson helicopter in-flight break-ups accidents in New Zealand had not been significantly reduced by the adoption of US Federal Aviation Administration measures intended to help prevent such accidents.
“We also found that the format of the Robinson flight manuals and terminology did not draw enough attention to safety critical instructions and conditions that could result in serious injury or death.
“Four of our earlier recommendations made as a result of Robinson mast bump accidents have yet to be actioned. We therefore remain concerned that there is a real risk that we will see more of this type of accident.”