Radarspotting

"Large parts of the UK are without any air ambulance cover after the main helicopter operator grounded services over safety fears.

Bond Air Services has withdrawn all 22 of its Eurocopter EC 135 helicopters over concerns about possible cracks in the rotor blades."

http://www.bbc.co.uk/news/uk-17993232

The original European Airworthiness Directive (AD) on this was 2012-0041R1 issued 15-03-2012.

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".

The 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."

Scottish air ambulances fly again after safety checks
http://www.bbc.co.uk/news/uk-scotland-highlands-islands-18000313

After the loss of the helo going to oil rig a few years ago they are more aware of failure.

Having spent more than twenty years on helicopter operations I can tell you that helicopter operators, both civilian and military have always been acutely aware of the possibility of rotor head failures.

The Super Puma crash on 1 April 2009 was not caused by failure of the MRH but by a failure of the second stage planet gear in the main rotor gearbox. The operator had already decided to replace the gearbox after a metal particle, originally thought to be a piece of scale, was found on a chip detector a few weeks previously. Sadly, a misunderstanding between the operator's engineers and the manufacturer led to the chip being misidentified as a particle of silver or cadmium plating and the frequency of inspections of the ring of chip detectors in the MRG was not increased.

The order grounding all EC 135 Air Ambulance helicopters has been lifted as of 0700hrs.,19/05/2012.
http://www.bbc.co.uk/news/uk-18000594
Regards-
G.B.