The lives of all helicopter operators in Northern Australia are at risk because a key engine component is wearing out much faster than it should — possibly because of a change to aviation gas composition — and it may cause a mid-air failure.

Key points: Helicopter engine cylinders are degrading after only a few hundred hours in the air

Helicopter engine cylinders are degrading after only a few hundred hours in the air CASA has warned pilots about the risks, which include mid-air failure

CASA has warned pilots about the risks, which include mid-air failure A stakeholder group has been formed to investigate the cause of the problem

The Civil Aviation Safety Authority (CASA) has warned pilots operating R-22 or R-44 helicopters in the northern regions of Australia about the risks, particularly those using them for mustering.

It is not yet clear if other operators of piston aircraft should take precautions.

Many in the aviation community have been privately expressing concerns for the past 12 months about the large number of helicopter engines with cylinders that have eroded or become damaged after only a few hundred hours in the air.

CASA has now declared it a problem, and stated it is seeing "increasing evidence of premature exhaust valve and valve guide wear, due to elevated combustion temperatures that will lead to degraded engine performance".

It is widely theorised the problem may be linked to the reduction of lead in aviation gas supplied to northern Australia a few years ago, from 0.86 to 0.56 per gram.

In 2017 there was a dramatic spike in sniffing of aviation fuel, particularly in one Indigenous community where children were breaking into the airport to steal AVGAS from aircraft.

The lowering of the lead content in AVGAS is now a main line of inquiry for a stakeholder group — made up of fuel manufactures, engine manufacturers, pilots, engineers, and CASA — that has been formed to investigate the engine problem.

CASA spokesperson Peter Gibson said they were looking into it as a matter of urgency.

"Clearly the change in the fuel specification has to be looked at and a number of people are pretty convinced that's causing the problem, although there are a range of variables so we don't want to rush into it until we've got the evidence," Mr Gibson said.

"A clear understanding of all potential causative factors need to be established before any solution can be recommended."

"It's also having an economic impact with helicopter companies now having to ground aircraft for longer durations and replacing cylinders more frequently."

The premature wearing of a helicopter engine component is putting musterers in particular at risk. ( ABC )

'It could cause someone to fall out of the sky'

John Armstrong, who has been a pilot for more than 30 years, said he knew of at least three incidents in the last 12 months where a helicopter had failed mid-air due to this particular issue.

"We have heard that there is some problems with this type of fuel 100, low lead they call it in America, but we have only heard that on the by and by," he said.

"But we are unique in the world with our R-22 population, in that we've got several hundred of these gadgets operating across a fairly hot temperature profile year round."

Andrew Lumsden, who is the chief engineer at North Australia Helicopters in the Northern Territory, said he had seen a huge spike in problems with cylinders in the past 18 months, most with very little hours on them.

"We've changed cylinders here that have as low as 98 hours from brand new," he said.

"It's a worrying trend on how quickly the valves are degrading and decaying due to the heat, or whatever it is, and ultimately it could cause someone to fall out of the sky and get injured."

Katherine Aircraft Maintenance Services owner Campbell Elliott, who has been a helicopter engineer for the past 20 years, said valves were breaking up in flight without warning.

"The only reason we pick it is because we are aware of the issue and we are doing these inspections more intensely then we have ever done," he said.

He and many others are concerned that it is only a matter of time before someone falls out of the sky.

"It has an effect on morale — you worry about it and sometimes you're lying at night there trying to figure out what the issue is," he said.