A North Sea pilot reported a near miss when a mystery helicopter passed under his aircraft.
It took investigators months to determine that a helicopter from a foreign warship was operating in the area before deciding there was no risk involved.
On February 5, a Sikorsky S-92 helicopter, flying from the Trans Ocean Galaxy II oil rig, was 110 nautical miles south-east of Aberdeen when the co-pilot noticed a radar contact showing no height information, which aircraft operating in the area always show.
A Civil Aviation Authority UK Airprox Board (UKAB) report said air traffic control in Aberdeen reported it had nothing on its radar although another helicopter confirmed they had the same contact.
Close to the Mearsk Curlew oil rig, the Sikorsky pilot saw what he incorrectly thought was a grey coloured Merlin helicopter.
The Royal Navy confirmed it was not operating in the area at the time. The report said a foreign air attache finally confirmed his country had an helicopter operating from a frigate in the area.
The UKAB report concluded the Sikorsky crew “probably misjudged the separation” as the other helicopter was seen to pass below through a hole in the clouds. It concluded “no risk of collision existed”.