The helicopter industry has grown in relation to North Sea oil activities. The two main operators are British Airways Helicopters and Bristows. Smaller companies include Kestrel, Ferranti and Management Aviation. Sikorsky 61N's and 58T's comprise the majority of aircraft used, with Bell 212's, Wessex 60's and some lightweight crafts filling out the fleet. Schedules for crew transportation and supply delivery are rigidly maintained, while air-sea rescue service still plays an important role in helicopter operations.