An Irish Coast Guard helicopter which had to make an emergency landing earlier this year may have been affected by turbulence from the Sperrin mountains, an investigation has found.
The report by the British Air Accidents Investigation Branch (AAIB) says that the helicopter pitch increased slightly before reducing, and the helicopter began to accelerate and exceeded its maximum speed.
The incident occurred on the afternoon of February 5th 2023, when the Sikorsky S-92 helicopter with four crew had departed from Sligo, Ireland, to rendezvous with a lifeboat near Portrush at approximately 1500 hrs.
The aircraft encountered unexpected severe turbulence approximately five nautical miles east-northeast of the City of Derry Airport.
The helicopter diverted to City of Derry airport and landed with no injuries recorded.
Damage (possibly pre-existing) to the helicopter resulted in the replacement of the stabiliser strut, aft tail drive shaft bearing support and forward tail drive bearing support
“An overspeed inspection of the helicopter identified three items which were rectified by the replacement of components,” the AAIB report says.
“The helicopter returned to service two days later. The manufacturer’s representative believed the findings likely pre-existed the overspeed event,” it says.
“Analysis of meteorological reports suggested that the helicopter ( EI-ICU) probably flew through mountain waves associated with the Sperrin Mountains, creating the turbulence which affected the helicopter,” it says.
“ Moderate turbulence was forecast in the region and discussed in the pre-flight briefing, but analysis of subsequent meteorological information suggested that mountain wave activity was present at the time of the event,” it states.
The helicopter returned to service two days after the event.
The full AIIB report is here