The Super Puma aircraft was about 20 miles south-east of Sumburgh Airport in Shetland when the gearbox problem emerged at 10.45am yesterday, causing emergency services to gather at the airport.
Shetland coastguard said the helicopter was carrying 20 people and landed safely shortly after 11am.
A spokeswoman said: "The helicopter landed safely at Sumburgh, it declared a pan-pan, what we call a full aircraft emergency, as a gearbox warning light had come on. It all kicked off about 10.45am. I'm not sure exactly where it was coming from but it was 20 miles south-east of Sumburgh and the ETA for it landing was 17 minutes later. There were 20 people on board and it landed safely, everything is fine."
The helicopter involved was a Superpuma EC225 operated by Bristow. A statement from the company said: "The aircraft was undertaking a routine crew change flight to an offshore installation and had 18 passengers and two crew on board at the time. The aircraft landed safely at Sumburgh Airport at approximately 11am and is currently undergoing a fault diagnosis to establish the required maintenance actions. The landing itself was uneventful but Sumburgh Airport mobilised the emergency services as a matter of routine.
"Flight safety is Bristow's first priority and we will always investigate prior to further flight."
A similar incident occurred in January when a CHC-operated Superpuma helicopter with 14 people on board issued an alert.