Airplanes and pets seem to have a lot in common. We love them, care for them, and develop a trusting bond over time. One might argue that an aircraft is not a living thing, but don’t argue that too loudly around those passionate owners that couldn’t imagine life without their trusted steed waiting for them in the hangar.
Airplanes and pets also have something else in common: They like activity. Being left alone for extended periods of time can generate some undesired behaviors in both. Case in point: My airplane recently had an avionics upgrade which, like many complex avionics “surgeries,” took about twice as long as expected. In my case, that meant that it didn’t move an inch for almost two months.
When my Bonanza and I were finally reunited, it did just what you would expect from a pet left too long alone: It peed on the floor.
Specifically, I noticed that things weren’t quite right during start-up. It caught fine and then stalled out twice in a row. Goosing the fuel pump a little, it finally settled into a smooth idle, but I knew something wasn’t right so I shut it down and went out to have a look.
Under the nose gear was a nice puddle of avgas with a fair amount of fuel being added to it dripping out of the bottom of the cowl. Lesson 1: When something doesn’t feel right, it probably isn’t. Play it safe and check out any anomalies as soon as possible, definitely before taking flight.
The fuel was leaking out of the fuel servo/metering valve on my fuel-injected Continental IO-550B. On closer inspection with the help of a friend in the cockpit, it was obvious that the O-rings had failed on the shaft that controls the amount of fuel fed to the fuel injectors (and linked to the throttle arm). This was sending copious amounts of fuel overboard at low throttle settings.
I routinely perform fairly thorough preflight, run-up, and post-flight inspections. So, I know that there was no significant leaking prior to this. In fact, there were no telltale blue stains on the bottom of the cowl that would have indicated that this was a slowly developing problem. And there was absolutely no work done on the engine while the airplane was in the avionics shop.
So, what does this tell us? It’s striking evidence of how airplanes can degrade over time when not routinely flown. I’m sure that this failure would have occurred even if I was flying regularly during those two months. However, it may have failed more incrementally and it’s certainly interesting that something so serious could fail in between flights separated by two months of sitting.
Lesson 2: Never assume that things are as you left them. Our aircraft are at their best when they are flown regularly. However, serious issues can develop between flights. And the longer in between those flights, the more likely something is to develop. Fuel evaporates, seals dry out, bare metal surfaces lose their protective oil film and grease hardens over time. Things are changing, even when we think they’re not and your airplane is not, in reality, as you left it.
So, if you are forced to leave your trusted companion alone for an extended period of time, do what you can to prepare it (lubrication, desiccant, engine “pickling,” etc.); but above all, be vigilant when you’re reunited. You’ll be understandably excited to get airborne again, but it pays to be safe.
Next time, we’ll go into more detail about that Continental fuel injection system, what went wrong, and what you can learn from it. Until then, happy flying!
Jeff Simon is an A&P mechanic, pilot, and aircraft owner. He has spent the last 14 years promoting owner-assisted aircraft maintenance as a columnist for several major aviation publications and through his how-to DVD series: The Educated Owner. Jeff is also the creator of SocialFlight, the free mobile app and website that maps over 20,000 aviation events, airport restaurants, and educational videos, including many how-to videos for the subjects of these articles.