operators of Sikorsky S-76 helicopters have been instructed to inspect the main rotor shaft repetitively for cracks after a cracked shaft was discovered during routine maintenance.

All models of the S-76 are affected by the US Federal Aviation Administration emergency airworthiness directive (AD). The cracked shaft was discovered during an inspection of the main transmission oil seal. The affected shaft had accumulated 477h.

Operators are required to conduct in situ dye-penetrant inspection of the shaft before further flights and after every 10 flights. They must inspect it visually daily. Any cracked shafts have to be replaced immediately, the AD says.

Sikorsky says a team has been formed to investigate the cause of the cracking. "This is not a grounding. There was no accident involved," the company stresses.

• Operators of up to 84 Raytheon Beech Barons and Queen Airs fitted with replacement elevator skins produced last year, and which did not receive the correct heat treatment during manufacture, have to replace the components under an AD issued by the FAA.

Source: Flight International