The Tutor
The Model 621 was powered either by a 155 hp (116 kW) Armstrong Siddeley Mongoose or Armstrong Siddeley Lynx IV (180 hp/130 kW) or IVC (240 hp/179 kW) engine; later Lynx-powered models had the engine enclosed in a Townend ring cowling. The Mongoose-powered version was called the 621 Trainer and the more numerous Lynx-engined aircraft the Tutor. The Tutor also differed by having a more rounded rudder.