EAA Sport Aviation - March 2011

• Eliminating most time between overhauls (TBOs)
and life limits in favor of condition monitoring
and failure prediction; and
• Recognizing that many component and subsys-
tem failures have acceptable consequences, and
that “run to failure” is often the best mainte-
nance strategy.

The shift from traditional to reliability-centered maintenance in the late 1960s and early 1970s was a watershed event. It resulted in massive reductions in maintenance expenditures and scheduled downtime by eliminating most TBOs and life limits and slashing both the amount and frequency of preventive maintenance. To the astonishment and disbelief of most maintenance experts of the time, component failures and unscheduled downtime plummeted.

This defied the conventional wisdom of the time. How was it possible that by doing less preventive maintenance to the aircraft, it actually became more reliable?

WWII OPERATIONS RESEARCH

It turns out that this seemingly counterintuitive result was discovered during World War II, more than 20 years before Nowlan and Heap did their pioneering studies. I was completely unaware of this until recently when Colleen Keller, a professional military operations analyst (and Cessna Cardinal owner) e-mailed me a fascinating paper written by Professor James P. Ignizio of the University of Texas that appeared in the September 2010 issue of Phalanx, the quarterly journal of the Military Operations Research Society (MORS).

In his paper, Professor Ignizio cited the little-known work of a gifted British scientist named Conrad Hal (C.H.) Waddington (1905-1975), who was a developmental biologist, paleontologist, geneticist, and embryologist—a rather unlikely person to make major contributions to the field of aircraft maintenance. During the war, however, Waddington’s career in biology was temporarily interrupted when he became involved in operations research for the Royal Air Force Coastal Command.

The principal assignment of Waddington and his fellow scientists in the Coastal Command Operational Research Section (CC-ORS) was to advise the British military on how it could more effectively combat the threat from German submarines. Waddington and his colleagues developed a series of astonishing recommendations that defied military conventional wisdom.