Waddington Effect — Uncertainty & RCM

Dibyendu De
Feb 24, 2017 · 2 min read

The initial birth pangs of RCM (Reliability Centred Maintenance) can be traced to the U.K. during World War II.

During that time, a British scientist named Conrad Hal Waddington (1905–1975) was conducting operational research for RAF (Royal Air Force). He was highly regarded for his analytical ability and critical thinking skills, which helped him to become a natural choice in the field of OR (Operational Research).

One of his first contribution was to determine the best colour of RAF bombers to keep them out of sight of German U Boats. He suggested that white would be the best choice. But as it happens to most good ideas it was met with initial resistance. But after the bombers were painted white the results were remarkable. The bombers were able to get 20% closer to the targetted U Boat before being spotted. This helped the British army to sink 30% more U Boats than that was previously possible.

His next contribution was even more significant. He recommended that the depth charges the bombers dropped be set to explode at 25 feet instead of the traditional set point of 100 feet depth. Once again he met strong resistance to implement his idea. But by decreasing the depth at which the charges detonated resulted in a seven fold increase in U-Boat sinking.

But his most significant contribution was yet to come. And it came in July 1943. He observed that British squadrons whose mission was to sink German U Boats consisted of 40 bombers. But at any given time, only about 20 of them were mission ready. Reasons for such unacceptably low readiness were varied. Some were waiting for spares. Some were waiting for maintenance personnel or undergoing scheduled maintenance activities. This was because, conventional wisdom dictated that more preventive maintenance was beneficial, i.e. more preventive maintenance would increase the reliability of the aircraft in a mission. In other words with better preventive maintenance we would eliminate unexpected breakdowns during a mission.

Waddington challenged this conventional wisdom. He and his team gathered data about scheduled and unscheduled maintenance performed on aircrafts and plotted the data. What they found surprised them since the facts did not support conventional wisdom.

At that time the bombers came in for routine preventive maintenance every 50 hours of flight hours. Waddington discovered that unscheduled breakdowns and repairs dramatically increased after each scheduled 50 hours service and declined steadily over time until the next scheduled 50 hour service after which they would again spike upwards.

Waddington had to conclude that the scheduled maintenance “tends to increase breakdowns and this can only be because it is doing positive harm by disturbing a relatively satisfactory state of affairs. Secondly, there is no sign that the rate of breakdown is beginning to increase again after the 40 to 50 flying hours, when the aircraft is coming due for its next scheduled preventive maintenance event.”

This came to be known as the “Waddington Effect.”

This was the beginning of the RCM (Reliability Centered Maintenance) school of thought and practice — a practice that embraced uncertainty as the cornerstone of its development.

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