PARIS, May 21 (Reuters) - European safety authorities have imposed checks or restrictions on two types of helicopter built by EADS subsidiary Eurocopter after separate incidents related to cracking, according to published safety bulletins.
The European Aviation Safety Agency (EASA) said it had ordered regular inspections around the base of the rotor blades of Eurocopter's EC 135 models after cracks were detected in a total of three helicopters.
The twin-engined civil helicopter is sold worldwide and extensively used by emergency services.
"This condition, if not detected, could lead to further crack propagation, possibly resulting in main rotor hub failure and consequent loss of the helicopter," EASA said in an emergency airworthiness directive.
In a separate emergency notice, it followed up on the ditching earlier this month of an EC 225 Super Puma helicopter in the North Sea.
The helicopter's crew put it down on water with 14 people on board on May 10 after seeing an oil pressure warning light.
The incident led to the temporary grounding of Super Pumas flown by the British operator of the helicopter involved in the ditching, Bond Offshore Helicopters.
EASA said preliminary investigations into the cause of the incident had discovered a crack on a shaft inside the gearbox.
The agency ordered operators to monitor data from a vibration monitoring system and restrict flights to daytime whenever such a system is not installed on their Super Pumas.
Bond Offshore Helicopters said it had already implemented the recommendations.
A spokeswoman for Eurocopter, the world's largest civil helicopter manufacturer, said that in both cases the two types of helicopter remained safe to fly.
Both investigations are still under way, she said.
"The safety of (both) helicopters is confirmed and flights are not suspended," the spokeswoman added.
Typically, such air safety directives incorporate recommendations already made by the manufacturer.
Eurocopter is the largest division of EADS behind Airbus and space company Astrium. It had revenues of 5.4 billion euros ($6.9 billion)in 2011 and has an order book worth 13.9 billion.
$1 = 0.7860 euro Reporting by Tim Hepher; Editing by Mark Potter