The European Aviation Safety Agency has issued an emergency airworthiness directive (AD) after a crack was detected on the lower hub-shaft flange of a Eurocopter EC135 main rotor during a routine inspection.
EASA says it requires checks to be carried out "before the first flight of the day, after the effective date of this AD and, thereafter, before each first flight of the day".
These checks should be "as specified in the applicable Rotorcraft Flight Manual, taking into account the instructions specified in section 1.E.2.(a) of Eurocontrol Deutschland's Alert Service Bulletin No.EC135-62A-029", the AD states.
EASA says the cause of cracking has yet to be determined but it has been established 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".
EASA's AD warns: "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."
This leads to a requirement for "repetitive flightchecks of the main rotor blade attachment bolts and safety pins to detect rotated bolts", says EASA.
"This 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 states, adding that if any abnormality is found it must be reported to EASA.