KLAMATH FALLS, Ore. --
Senior Master Sgt. Brian Stroup from the 173rd Fighter Wing Quality Assurance Office was quite a ways from his desk, where his supervisory role usually keeps him. At the senior enlisted rank of E-8 he didn't often have the chance to crawl back underneath a jet. Here he was with the jets at End-of-Runway, the last stop before they climb into the sky for their training missions, opening hatches like he used to do when he was a younger maintenance troop. He opened the hatch housing the generator of the waiting F-15 and saw smoke and read a temperature of 326-degrees Fahrenheit, way outside safe operating range. He turned the jet back to the ramp and returned to his office where his staff was coming to grips with a chronic problem of generator failures due to overheating.
The quality assurance office tracks trends where safety, flying, and money coincide. Their tracking revealed a large number of unexplained generator heat failures, which was strange because an F-15 generator has a dedicated cooling system.
Master Sgt. Brett Lundberg traced the problem to that cooling system. He knew that in many cases it simply quit working and caused a fail-safe solder connection to melt, requiring an expensive depot-level maintenance fix. To make matters worse, the F-15 depot was swamped with orders for this part and was only able to turn out one to two a month--it was a fleet-wide problem. He knew a local fix would save money and forestall any impact on the flying mission.
Lundberg had the offending part, a heat-actuated bypass valve that controls the flow of coolant to the generator, on his desk and torn down to its individual pieces. According to the technical order it was assembled correctly, and seemed to be in perfect working order.
"When we broke down these cooling units that had overheated they were filled with insoluble sludge," revealing the part wasn't doing its job Lundberg noted. "I had to investigate what was happening in this part to find the root cause."
Searching for that cause led him along a twisting path. It had them in the break room running water through the faulty part, it had Lundberg researching valve actuators after work, and finally it led to a realization.
"'What if these simple little washers are bi-metal disks?'" Lundberg asked himself. A bi-metal disk is made to arch when heated. "I threw one on the barbeque downstairs and sure enough, it changed shape."
It was a breakthrough because then he understood how the bypass valve opened or closed. There were eight pairs of these bi-metal disks that look like washers, arranged to open the valve allowing coolant oil to circulate around the generator. But if each disk isn't properly situated to press on the one next to it, then the valve wouldn't open. And so the members of the 173rd QA shop surmised that there was a problem with the way these little washers were placed.
The technical order--a detailed set of instructions on how to assemble a part--didn't specify that these small washers needed to be assembled in any particular fashion.
"I took the actuator switch apart knowing that it needs to go back a certain way and I dropped three of the washers," said Master Sgt. Israel Mackey, Lundberg's coworker. "There is no way that left to chance these would end up reassembled properly."
And so, by rigorous investigation, the 173rd Quality Assurance Office revealed the very root of the problem, a small metal disk the size of a quarter. When those eight disks didn't function properly the valve to circulate the coolant never opened, the heat from the generator wasn't dissipated, and jets that were ready to fly, in every other respect, couldn't.
At this point they knew the process here and around the fleet needed to change. Mackey wrote a detailed change to the technical order for distribution to all the units currently flying the F-15. That request was approved and will soon help the entire F-15 fleet worldwide avoid a costly problem.
When asked to distill how they solved the problem, Lundberg says it's simply a matter of looking at the problem, seeing what information you can gain and then being willing to follow that information down the path to its logical conclusion.
"Once you start down that path it will lead you to the solution," said Lundberg.