Maintenance Induced Failure

Changing Warrior 481's oil, 17 August 2021

With the master switch on and the boost pump running to build sufficient fuel pressure, I cracked the throttle, pushed the mixture to rich, gave the engine three shots of prime, and engaged the starter. The engine turned over enthusiastically, but showed no interest in firing. Not a single grunt, roar, or snort.

I had fuel pressure and plenty of oomph in the battery to turn the engine over, but there was no response. The behavior was reminiscent of trying to hot start the engine with a bad coil in the left mag. But with a SureFly installed in that position, that was not the problem this time. Regardless, I suspected that I was not getting spark. After checking under the cowling to ensure that the SureFly was still wired to power, I regretfully pushed Warrior 481 back into the hangar and bummed a ride to Dansville with Paula and Steve where we joined several others for a Friday night ice cream run.

20 August 2021: Riding right seat with Paula, returning from ice cream in Dansville.

Early the next morning, I returned to the airport and explained the problem and my observations to Ray. We checked the voltage at the SureFly and discovered that there was none. No power = no spark. A check of the 10 A inline fuse on the power wire from the battery to the SureFly revealed a broken fuse. No shorts between that line and the airframe (ground) could be found and replacing the fuse immediately fixed the problem.

But why did it blow in the first place and what assurance did I have that it would not likely happen again?

Peering under the cowling, Ray had an epiphany. "Did you say that you just changed the oil?"

Photo of the unmounted engine from July 2020 showing the placement of the SureFly and the oil filter.

I had. The Warrior was actually overdue when we returned from Hilton Head Island on August 14 and I dumped the oil as soon as the airplane was back in the hangar before getting my family home for dinner. I returned on the evening of  August 17 to finish the oil change. 

Ray pointed out how close the power terminal on the SureFly was to where I routed the braided safety wire to the oil filter. Our best explanation is that I inadvertently shorted the power terminal on the back of the SureFly to ground either while removing the old filter and wire or wiring the new filter into place. There was surely a spark in that moment given enough current to pop a 10 A fuse, but I never saw it. Because I finished the oil change late at night on the 17th, I deferred the usual post-maintenance run up to another time. Otherwise, I should have discovered the issue at that time.

Ray put a silicone boot over the terminal to prevent repeat occurrences.

Maintenance induced failure is a phrase that is often used to caution pilots against performing unnecessary work on their aircraft. Obviously, oil changes are necessary maintenance and no one is arguing against doing them. But truly, any maintenance poses a risk of changing or breaking something unexpectedly.

In my case, this incident underscores something that I already know well: the need to carefully assess an airplane after performing even light maintenance. Fortunately, Ray was immediately available to help troubleshoot. I certainly did not want to miss out on my date with the stealth fighter just a few days later.

Post oil-change sunset on 17 August 2021.