A number of airlines throughout the world will, in the near future, be reconditioning and testing Dart engines from Viscount, Friendship and Herald aircraft. In most cases the testing will employ a technique which has been in use at the Rolls-Royce Australian overhaul base at Sydney, N.S.W., since August 1954. This is based on the torque reaction of the engine to the propeller and is suitable for testing any comparable engine.