Excluding certain personalities, AvGas is the most explosive part of your piston-powered airplane. For the energy that AvGas contains, it actually can pose a significant threat to the safety of flight. This is the reason why pilots and FBOs alike have a healthy respect for airplane fuel, and work to assure that there are no leaks to be seen or smelled.
SOMETIMES, IT ISN’T A LEAK THAT CAN GET YOU. Take our friend’s aircraft for example. Joe’s FBO had just completed the installation of a factory rebuilt engine for his airplane. He spent the extra money for the factory “rebuilt” engine (as opposed to a factory or field overhaul) because he wanted a zero-timed engine, and wanted to avoid potentially using some of the original parts that had been flying around for 4,000-odd hours in his current engine.
SOUND THINKING. Joe has always done right by his plane. He kept it up with fastidious maintenance, he changed out parts and overhauled components at the intervals recommended by his aircraft’s manufacturer. He felt that by using this approach, he would improve his chances of making each and every trip safely. This, in turn, provided him with a little peace of mind each time he flew.
THE SHOP HAD DONE A GOOD JOB OF INSTALLING THE ENGINE. The old engine had been removed, the engine compartment was cleaned and primed, all the hoses, mounts and control cables had been replaced, and the new engine had been installed. With new baffles around the engine, it looked as if it was ready to fly.
Before Joe picked up the plane, the shop had started the engine several times, looking for leaks and problems. After these running checks, the shop called Joe and told him it was ready for his first post-new-engine flight.
Joe arrived at the airport minutes later, with his flight bag and headsets in hand. He performed a thorough preflight of the plane, and found no problems. With the preflight behind him, Joe strapped in and fired up the engine. To his delight, the engine started up quickly, with only a few turns of the prop.
Following his checklist, Joe waited until the ammeter dropped off, and then turned on his avionics master. He throttled up the engine to taxi out to the active for the runway, and slowly made his way to the run up area. From there, he increased the engine speed to 1700 RPM, and began his mag checks … when he noticed two disturbing things.
- His fuel computer had just failed, and its display was indicating a sensor error.
- Thick smoke was now coming out of his engine cowl!
JOE QUICKLY SHUT DOWN THE ENGINE AND JUMPED OUT OF THE PLANE. He looked inside the cowl, and saw something glowing on the top of the engine. By that time, a crew from the FBO had arrived with a fire extinguisher, but the smoke had stopped. The plane was towed back to the FBO’s hangar for inspection.
WHEN THE COWL WAS REMOVED, everyone was shocked by what was found. The fuel computer transducer sat on top of the engine, and it was badly discolored. The wires to the fuel transducer were burned bare of insulation, and the phenolic cover of the transducer was melted!
The mechanic was at a loss to explain it, until he took a good look at the engine. That is when the head mechanic noticed there was no ground strap between the engine and the airframe! This meant that as the engine speed was increased, the ground path to the alternator was through the only other electrical connection on the engine — through the fuel computer transducer. The 20-gauge wires to the fuel computer took the load, and created the black smoke as they overheated and began to glow. The fuel computer transducer took a heavy current load as well, and was destroyed in the bargain.
HOW CLOSE WAS JOE TO A FUEL FIRE? Pretty darn close! Had the fuel transducer heated up more, the fuel inside could have ignited and caused an explosion. Had there been a weak spot in the transducer, a leak of high-octane AvGas on top of the engine might have developed. In either case, the prognosis for the aircraft would not have been good.
WHAT CAN YOU DO TO AVOID THIS PROBLEM?
- Following an annual or any work that requires removal of the engine make a careful inspection to assure the ground cable is attached BOTH to the engine AND the airframe.
- Carefully monitor for unexpected events when you bring your plane back from engine work … this includes when the engine is first started, as well as when the alternator and avionics master are turned on, or engine load is increased.
- Take your time on the ground during these tests. The best time to find out that you have a problem is when you can still walk away from it. Once the plane is airborne, your options become very limited.
JOE GOT LUCKY IN THIS CASE. The damage occurred on the ground, and the FBO sheepishly apologized and made the repairs. If the plane had been in flight, the story might have been very different. Think about the last time you had major engine work. Did you check out the ground strap, or did you just assume it would be okay because you trust the FBO? Did you perform a preflight as good as or better than the manual called out, or did you kick the tires and light the fires? If you find yourself answering more of the latter than the former, you need to think about what happened here and change your behavior after any work is done on your airplane or the one you rent. Otherwise, you may find yourself facing the same daunting challenge that confronted Joe.
