Crack Was Detected On The Lower Hub-Shaft Flange Of A Main Rotor Hub (MRH) Shaft

EASA has issued an emergency AD applicable to some Eurocopter EC 135 and EC 635 model helicopters.

During a periodical inspection of an EC 135 helicopter (pictured in file image), a crack was detected on the lower hub-shaft flange of a main rotor hub (MRH) shaft. The investigation is on-going and the cause of the cracking has not been determined yet. It has been established, however, that deformed safety pins, used to secure main rotor blade bolts, can indicate that bolts may have rotated, indicating possible cracking in one of the hub-shaft flanges.

This condition, if not detected and corrected, could lead to further crack propagation, possibly resulting in main rotor hub failure and consequent loss of the helicopter.

For the reason described above, the Emergency AD requires repetitive pre-flight checks of the main rotor blade attachment bolts and safety pins to detect rotated bolts. In addition, the AD requires a one-time visual inspection of the upper and lower hub-shaft flange for cracks and, if cracks are detected, replacement of the main rotor hub. The AD also requires reporting of any findings to ECD. EASA said in its notice that the AD is considered to be an interim action and further AD action may follow.

The AD is effective immediately.

FMI: www.easa.europa.eu