The Civil Aviation Safety Authority (CASA) has issued a serious warning to helicopter pilots.

CASA says a key engine component is wearing out faster than it should in R-22 or R-44 helicopters, and may cause a mid-air failure.

Reports say a large number of helicopter engines are turning up with eroded cylinders after just a few hundred hours in the air.

CASA has now officially declared it a problem, stating there is “increasing evidence of premature exhaust valve and valve guide wear, due to elevated combustion temperatures that will lead to degraded engine performance”.

Some believe the problem is linked to recent standards that have reduced lead in aviation gas supplied to northern Australia from 0.86 to 0.56 per gram.

Lead levels were lowered after a dramatic spike in the sniffing of aviation fuel (AVGAS).

The new AVAGS lead content is a central point of inquiry for a stakeholder group comprising fuel manufacturers, engine manufacturers, pilots, engineers, and CASA, which has come together to investigate the engine problem.

CASA spokesperson Peter Gibson says it is 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.”