SolutionThroughout the 1960's and 1970's, many program managers learned the hard way (though experience) that power supplies were the critical-path item on their program, causing embarrassing schedule slips and cost overruns on an otherwise successful program. Unfortunately, people talk about their successes and not their failures, especially when it is something as embarrassingly simple as a power supply. Hence, the trouble with power supplies was one of the best kept secrets of these decades.
But the Navy was keeping score and by 1979 had determined "Failure data suggests that fleet readiness could be improved as much as 20% if electronic power supplies simply met their specified mean times between failures in service use." P4855-1, page 1
To put it in stronger terms, if only power supplies met their allocated field reliability, it would be equivalent to adding a couple of aircraft carriers to the fleet -- complete with a full compliment of aircraft, munitions, and crew -- at no extra cost to the taxpayer. The Navy then went on to contact 170 Navy power supply design activities, convened a panel of experts to work on solutions, and published the solutions in Navy Power Supply Reliability - Design and Manufacturing Guidelines [1], arguably the widest read document ever written on power supplies. Once the problems were aired, contractors admitted they had the same problems on Air Force, Army, NASA, and commercial programs as they had on Navy programs. The problems with power supplies were widely discussed and solutions found and implemented. By 1989, the Navy could claim that power supplies were no longer the number one failure item in the fleet. But before this occurred, some remarkable things happened. Prior to the release, and in anticipation of Navy Power Supply Reliability - Design and Manufacturing Guidelines [1], the Navy released NAVMAT NOTICE 3080 [3], which, among other things, required a Navy Program Manager's procuring activity to investigate and justify any program that did not meet certain criteria. These criteria included: "The development schedule shall allot at least 18 months from power supply specification release to production start, including completion of qualification and reliability growth screening." "At least 10% of the total electronic system development cost, excluding software, shall be budgeted to the power supply function."
These are remarkable requirements. To the best of my knowledge no program manager had ever been constrained before or since to allocate a specific percentage of their resources to a specific function. There were probably few program managers who were allocating this much to power supplies or who wanted to do so -- they thought they had better use for their money. To further make program managers aware, if the schedule was less than 12 months or the funding less than 5%, special approval had to be obtained from the Deputy Chief of Navy Material, Reliability, Maintainability, and Quality Assurance (then Mr. W. J. Willoughby, Jr.). And this was no rubber stamp approval. The program manager had to explain to people knowledgeable of the history of past problems why their program was different. If he could do that, no problem, but he had to do his homework. The bottom line is that this established awareness at the highest program management level. The above illustrates the steps the Navy took in making program managers and subordinates aware of serious power supply problems. After making them aware, a plan was provided, Navy Power Supply Reliability - Design and Manufacturing Guidelines [1], that was designed to reduce the risk of the problem to acceptable levels (power supplies meeting their allocated reliability in the field). History often repeats itself when the members of the current generation do not have knowledge of the problems of past generations. The 1980's decade saw the recognition and solution of a serious reliability problem with power supplies. Power supplies are still a serious design and application problem. Not being aware of the potential problems and the ways to reduce risk leave any present program manager susceptible to their worst nightmares - schedule slips, cost overruns, and poor field reliability. Disclosure: I was on the committee that wrote the first edition -- but that does not mean I agree with everything. Never-the-less, it is one of the better committee efforts concerning power supplies. If you read the document and see something that has been overtaken by events or is wrong from your viewpoint, don't reject the whole document. Much of it is still relevant. Do not use this information for design without independent verification of the information. Editor: Jerrold Foutz |
