" GA Needs a New Story
The Dream Delayed "
The Waddington Effect
January 14th, 2014 by Mike Busch C.H. Waddington (1905-1975)
In 1943, a British scientist named Conrad Hal (C.H.) Waddington made a remarkable discovery about aircraft maintenance. He was a most unlikely person to make this discovery, because he wasn't an aeronautical engineer or an aircraft mechanic or even a pilot. Actually, he was a gifted developmental biologist, paleontologist, geneticist, embryologist, philosopher, poet and painter who wasn't particularly interested in aviation. But like many other British scientists at that time, his career was interrupted by the outbreak of the Second World War and he found himself pressed into service with the Royal Air Force (RAF).
Waddington wound up reporting to the RAF Coastal Command, heading up a group of fellow scientists in the Coastal Command Operational Research Section. Its job was to advise the British military on how it could more effectively combat the threat from German submarines. In that capacity, Waddington and his colleagues developed a series of astonishing recommendations that defied military conventional wisdom of the time.
For example, the bombers used to hunt and kill U-boats were mostly painted black in order to make them difficult to see. But Waddington's group ran a series of experiments that proved that bombers painted white were not spotted by the U-boats until they were 20% closer, resulting in a 30% increase in successful sinkings. Waddington's group also recommended that the depth charges dropped by the bombers be set to explode at a depth of 25 feet instead of 100 feet. This recommendation - initially resisted strongly by RAF commanders - ultimately resulted in a sevenfold increase in the number of U-boats destroyed.
Consolidated B-24 "Liberator" bomber
Waddington subsequently turned his attention to the problem of "force readiness" of the bombers. The Coastal Command's B-24 "Liberator" bombers were spending an inordinate amount of time in the maintenance shop instead of hunting U-boats. In July 1943, the two British Liberator squadrons located at Ballykelly, Northern Ireland, consisted of 40 aircraft, but at any given time only about 20 were flight-ready. The other aircraft were down for any number of reasons, but mostly undergoing or awaiting maintenance - either scheduled or unscheduled - or waiting for replacement parts.
At that time, conventional wisdom held that if more preventive maintenance were performed on each aircraft, fewer problems would arise and more incipient problems would be caught and fixed - and thus fleet readiness would surely improve. It turned out that conventional wisdom was wrong. It would take C.H. Waddington and his Operational Research team to prove just how wrong.
Waddington and his team started gathering data about the scheduled and unscheduled maintenance of these aircraft, and began crunching and analyzing the numbers. When he plotted the number of unscheduled aircraft repairs as a function of flight time, Waddington discovered something both unexpected and significant: The number of unscheduled repairs spiked sharply right after each aircraft underwent its regular 50-hour scheduled maintenance, and then declined steadily over time until the next scheduled 50-hour maintenance, at which time they spiked up once again.
When Waddington examined the plot of this repair data, he concluded that the scheduled maintenance (in Waddington's own words) "tends to INCREASE breakdowns, and this can only be because it is doing positive harm by disturbing a relatively satisfactory state of affairs. There is no sign that the rate of breakdowns is starting to increase again after 40-50 flying hours when the aircraft is coming due for its next scheduled maintenance." In other words, the observed pattern of unscheduled repairs demonstrated that the scheduled preventive maintenance was actually doing more harm than good, and that the 50-hour preventive maintenance interval was inappropriately short.
The solution proposed by Waddington's team - and ultimately accepted by the RAF commanders over the howls of the maintenance personnel - was to increase the time interval between scheduled maintenance cycles, and to eliminate all preventive maintenance tasks that couldn't be demonstrably proven to be beneficial. Once these recommendations were implemented, the number of effective flying hours of the RAF Coastal Command bomber fleet increased by 60 percent!
Fast forward two decades to the 1960s, when a pair of gifted scientists who worked for United Airlines - aeronautical engineer Stanley Nowlan and mathematician Howard Heap - independently rediscovered these principles in their pioneering research on optimizing maintenance that revolutionized the way maintenance is done in air transport, military aviation, high-end bizjets and many non-aviation industrial applications. They were almost certainly unaware of the work of C.H. Waddington and his colleagues in Britain in the 1940s because that work remained classified until 1973, when Waddington's meticulously-kept diary of his wartime research activities was declassified and published.
Next time, I'll discuss the fascinating work of Nowlan and Heap on what came to be known as "Reliability Centered Maintenance." But for now, I will leave you with the major takeaway from Waddington's research during World War II: Maintenance isn't an inherently good thing (like exercise); it's a necessary evil (like surgery). We have to do it from time to time, but we sure don't want to do more than absolutely necessary to keep our aircraft safe and reliable. Doing more maintenance than necessary actually degrades safety and reliability.
Mike Busch is arguably the best-known A&P/IA in general aviation, honored by the FAA in 2008 as National Aviation Maintenance Technician of the Year. Mike is a 7,500-plus hour pilot and CFI, an aircraft owner for 45 years, a prolific aviation author, co-founder of AVweb, and presently heads a team of world-class GA maintenance experts at Savvy Aviator. Mike's book Manifesto: A Revolutionary Approach to General Aviation Maintenance is available from Amazon.com in paperback and Kindle versions.
Tags: general aviation, maintenance, ownership, preventive maintenance, reliability, reliability-centered maintenance, safety, Waddington Effect
on Tuesday, January 14th, 2014 at 2:44 pm and is filed under Aircraft ownership and maintenance, Authors, Mike Busch, Trends and analysis.
The opinions expressed by the bloggers do not reflect AOPA's position on any topic.
Jong
This dovetails into tales of woe when flying aircraft right out of "routine" 50/100/annual.
 Mike Busch
Indeed! I will be doing a future blog post about post-maintenance test flights. By far the most likely time to have an in-flight mechanical failure is on the first flight after maintenance. If I were FAA Administrator for a day (which ain't gonna happen), I'd change the regs to require mechanics to go up on the first flight after any maintenance they performed.
Mike Shiflett
Hey Mike...back in 1973 I started a avionics technician job at the old Hangar One facility in Atlanta, Ga. My boss, Chuck McCorvey always told us to make sure we did the job right because we'd be the first to ride in it after the repair. As you can tell, to this day those words never have left my mind.
When my Dad was at Biloxi in 1944 no one flew an aircraft straight from the shop. They had a couple of older vets fly everything first. At my glider club the Chief Pilot flies gliders just assembled or maintained. Of course the greatest argument was the old TV show "The A Team". The pilot would ask about some piece of junk that George Peppard had dug up for a mission. If George went on about all the things that had been fixed, the pilot would resist: "I don't like airplanes that have been worked on." Everyone found that line pretty funny except pilots.
Or, in redneck terms, "If it ain't broke, don't fix it!
I had an A&P/IA replace my wing struts with new sealed units to prevent against "possible" corrosion in the struts. He did a good job until I took off and performed my first takeoff, pattern and landing while maintaining a continuous 30-degree cross-controlled yaw to the left! He had forgotten to re-rig the plane; I nearly re-rigged my keester!
Larry G
Or, as some companies seem to go... "If it ain't broke, we'll fix it till it is!"
Billy C
Curious. Just wonder if the data collected included causes of increased unscheduled maintenance. Mix match of new and used parts? Mechanic errors? Etc.
Mechanic errors played a big part in it, particularly errors of omission (e.g., failure to tighten or torque, failure to safety).
John Worsley
It also dovetails with the failure rate within 50 or so hours of an overhaul or one of the FAA's mandatory inspections of parts that have an extremely low failure rate.
Yes, the rate of such "infant-mortality" and "maintenance-induced" failures is much higher than generally believed. I'll get into that in my blog post next month.
Max W
The Waddington Effect: reminds me of what my A&P has been telling me since I purchase a used LSA two years ago. If it ain't broke leave it alone (don't fix it)!
Your A&P definitely has the right idea. Most maintenance should be done on-condition, not on some fixed timetable (although there are a few exceptions).
Vernon Lewis