Warning after fatal Tas helicopter crash

Operators of Huey helicopters are being urged to inspect their aircrafts' drive shaft after a fatal crash during bushfire fighting efforts in northern Tasmania.

The Australian Transport Safety Bureau (ATSB) has issued the safety advisory notice recommendation for UH-1H (Huey) helicopters.

It comes amid an investigation into an accident involving a Huey during firebombing operations near Launceston in February that killed an experienced 41-year-old pilot.

A preliminary report released in April noted the helicopter was spotted encountering mid-air problems moments before the crash.

The ATSB says further examination of the wreckage determined the main drive shaft failed, with evidence of severe frictional and wear damage to one portion.

ATSB director of transport safety, Stuart Macleod, said formal findings were yet to be made and inspections of the KAflex shaft was ongoing.

"The drive shaft's manufacturer has advised the ATSB that the presence of frictional damage is evidence that the shaft had entered fail-safe mode during operation," he said.

The KAflex drive shaft was manufactured by Kamatics Corporation in the early 1980s as part of a US Army UH-1H retrofit program.

Several KAflex drive shaft failures prompted America's Federal Aviation Administration to issue an airworthiness directive to UH-1H operators, which from February 25 required them to replace the shaft before further flight.

"While the specific circumstances of this accident are still under investigation, the ATSB advises UH-1H operators to note the preliminary details of this accident (and) the (American) airworthiness directive," Mr Mcleod said.

"(Operators should) look for the presence of corrosion, fretting, frame cracking and missing or damaged flex-frame attaching hardware during all inspections of the KAflex drive shaft."

The ATSB has advised UH-1H operators to familiarise themselves with a Civil Aviation Safety Authority bulletin which recommends closer inspection of the drive shaft.

The bulletin was re-issued in June last year after a separate accident in which a UH-1H conducted a forced landing after a drive shaft failure.