ALL 19 people on board a helicopter that ditched into the North Sea have been safely accounted for, the coastguard has said.

The aircraft operated by Canada-based CHC Helicopter was carrying an oil-change crew from Aberdeen to West Phoenix rig when it came down 32 miles south of Shetland, off Fair Isle, at around 3.30pm.

It is understood the pilot sent out a mayday after deciding the helicopter, carrying 17 rig workers and two crew, had to make a controlled ditching in what Shetland coastguards describe it as good, calm weather.

The latest emergency has caused new safety concerns as it emerged the same Super Puma EC225 type helicopter and its older variation, the AS332, has been directly involved in a series of accidents that have led to deaths and grounding of fleets.

The worst of these was in April 2009, when an AS332L2, returning from BP's Miller oil platform, suffered apparent gearbox failure and crashed off Peterhead, killing all 16 people on board – two pilots and 14 oil workers.

The latest accident comes one week after an Air Accidents Investigation Branch report recommended Marseilles-based Eurocopter, the manufacturer of the EC225, should be required by the European Aviation Safety Agency to review the design of the main gearbox lubrication system after an emergency landing in May.

Jake Molloy, offshore organiser for the RMT union, said after previous incidents in "a little over three years" was "bound to cause a bit of concern on the ground".

First Minister Alex Salmond said an investigation was required to discover if any lessons needed to be learned from what happened.

It is understood the pilot had spotted the Nord Nightingale offshore vessel and told the ship's crew he was bringing the helicopter down. The ship immediately sent its fast rescue craft to the scene and retrieved all of those on board.

No-one was injured in the ditching and those on board were taken by helicopter to Kirkwall in Orkney, the coastguard said.

A statement from CHC Helicopter said: "We can confirm that there has been an incident involving one of our aircraft in the North Sea. Exact details of the incident are not yet known."

Balpa, the professional pilots union, said: "Today's incident again highlights the importance of trained flight crew. It appears the pilots performed a controlled ditching into the North Sea which is an extremely challenging manoeuvre."

Some of the passengers on board the Super Puma recalled their ordeal.

Michael Mashford, a security officer on board the West Phoenix drilling rig, said there was no panic and the pilots were fully in control of the situation.

Jorn Gudbrandsgard, from Norway added that after working offshore for 12 years, he was on the flight to his last shift. "When we came through the cloud cover I was happy to see that the water was very calm, everything went very smoothly.

"After two or three minutes on the water, the floats of the helicopter were inflated and we opened the door. We got into the liferaft, there was no racing or panic and people were helping each other. I think we are extremely lucky today."

A spokesman for Eurocopter, said it was investigating the incident with the operator and authorities "with the highest priority".