The EASA has issued an emergency Airworthiness Directive (AD) calling for inspections of all Eurocopter EC135s after a crack was discovered on the lower hub-shaft flange of a main rotor hub shaft on one of the light twin-engine helicopters. In issuing the emergency order, the agency wants to avoid crack propagation, which could cause hub failure.
The investigation has already found that deformed safety pins, used to secure blade bolts, indicate that bolts have rotated. In turn, this indicates possible cracking in one of the hub-shaft flanges. Therefore, before each first flight of the day, blade attachment bolts and safety pins should be checked.
In addition, the AD requires a one-time visual inspection of the upper and lower hub-shaft flange. If cracks are detected, the hub must be replaced. The visual inspection should be performed within 100 flight hours or three months. Any finding must be reported to Eurocopter. The AD, effective yesterday, refers to a Eurocopter alert service bulletin. The investigation is ongoing and further ADs might follow, the EASA added.