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Clear air turbulence and thunderstorm turbulence are compared. The flight technique to be used is the same in all turbulence. Upsets in thunderstorm turbulence are discussed. Years ago there was evidence of a clear pattern in the upsets involving propeller driven airplanes. There was heavy airplane nose down elevator use following a violent updraft with eventual recovery from a deep dive. A similar pitch axis pattern is apparent in jet upsets. The swept wing jet has different stability characteristics; has a motor driven horizontal stabilizer as well as an elevator to control around the pitch axis; has improved flight instrumentation. Pilot training and a stabilizer modification have contributed to a dramatic decline in incident reports.

THE feathering propeller meets two fundamental needs in airline operation which the constant-speed propeller cannot meet, the authors explain. First, by stopping the rotation of an engine and propeller in flight, it protects the airplane from catastrophic vibrations occasionally set up by mechanical failures of engine and propeller. And the second fundamental need, they state, is that the feathering propeller decreases the drag of an inoperative propeller, thereby increasing the performance of a multiengined airplane with one or more engines inoperative. For these reasons, they point out, the feathering propeller has been accepted by leading airlines as the answer to their immediate propeller needs. In this paper the full-feathering principle is explained as applied in two distinct propeller designs.