Air ambulances covering large parts of the UK have been grounded after a fault was found which could cause them to crash.
Flights of 22 Eurocopter EC 135 helicopters have been suspended as a precaution, operator Bond Air Services said, following the discovery of a fault in an air ambulance in Scotland last month.
A crack was discovered on the main rotor hub of one helicopter, prompting a safety warning by the European Aviation Safety Agency (Easa).
Bond said Eurocopter had advised pre and post-flight checks after the fault was discovered but Bond had now decided to halt flights until further notice on safety grounds.
"The company's first priority is safety and it has reported its decision to suspend the flights of the EC 135 to Eurocopter and awaits further comment from Eurocopter once they have completed their investigation," a spokesman said.
About 1,000 of the craft are in use around the world, including air ambulance services in England, Scotland and Wales.
In England, the model is in use at Thames Valley and Chiltern; North West; Midlands; Dorset and Somerset; Hampshire and Isle of Wight; and Devon, according to the Association of Air Ambulances.
Eurocopter said it was giving its investigation into the EC135 its "highest priority".
The model, of which there are more 1,000 in operation in the world, has an "excellent safety record", a spokeswoman said.
"Eurocopter is, at this stage, not able to comment further within the scope of the investigations and is devoting all of its efforts in order to identify the cause in close collaboration with the operator and the EASA," she said.
"Safety is, and has always been, Eurocopter's top priority. We expect our suppliers to demonstrate the same level of commitment in this respect, and we share this culture with our customers to ensure that day in, day-out, thousands of operators around the world make safe flights."
In its directive, the EASA said: "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."
There are currently 30 helicopters in service for the 18 Air Ambulance charities in England and Wales plus two operated by the Scottish Ambulance Service, according to the AAA.
Bill Sivewright, the chief executive of the Dorset and Somerset Air Ambulance and vice chairman of the Association of Air Ambulances, said 16 air ambulances were affected.
Services with aircraft affected were working with those with helicopters still flying to provide as much cover as possible, he added.
"For us here, we are coping," he said.
"It is all hands to the pumps when these things happen. We are used to working together so when these things happen we can respond.
"No one can pretend it is everything we want it to be. But I would rather be in this position than cleaning up after an accident."
The Hampshire and Isle of Wight Air Ambulance was still flying, he said, because it was already using a different replacement aircraft while its EC 135 was undergoing maintenance unrelated to the safety concerns.