Mr. J. D. Siddeley in a paper on the reliability of aircraft engines in the Journal of the Royal Aeronautical Society for March, 1925, says under the heading Reduction Gears: “ The inclusion of this component has been responsible for limiting seriously the degree of reliability of the power unit. Considerable progress has been made, but the difficulties have by no means been solved. A stage existed when this component controlled the period between inspection and overhauls on the power unit. Improvements in the method of manufacture, particularly as affecting tooth form, have been responsible for a very considerable increase in the degree of reliability, but it is suggested that it represents one of the chief factors controlling the standard of reliability of the power unit as a whole.”

This statement is sufficiently serious ; coming from so great an authority on aircraft engines it compels attention and investigation.