When Your Aircraft Speaks, Be Sure to Listen Closely


On my trip back from Naples, I sensed there was a just a touch of vibration during cruise flight. It was almost imperceptible. Was it just my imagination? I tried different mixture settings and power settings, and then different RPM’s. Still, things did not seem quite right.

All the engine parameters on the Conti IO-550B were completely normal. Oil pressure was within limits, as was the oil temp. Did the engine cowling latch come partially undone? Was I about to throw and alternator or AC belt? Were the cowl flaps resting on the exhaust pipes?

Anyway, I put it out of my mind until I landed at dusk at KLEE, and taxied the bird to the ramp. Then I saw it… a small stream of liquid dribbling along the hangar floor from under the engine as I pushed the Bonanza back into her hangar.

I swiped my index finger through the liquid, smelled avgas and immediately opened the engine cowling on the pilot’s side. With a flashlight I started searching the engine compartment for the source of the fuel leak.

Within a minute or two, I found the problem. There were blue fuel stains on the TCM fuel manifold and on the top of the engine case. The fuel manifold, or spider, is part of the fuel injection system on many aircraft engines. This spider valve takes fuel from the engine driven pump and force feeds it through individual stainless steel lines, attached to injectors in each cylinder head.

Apparently one of the seals failed within the manifold, creating the leak and causing an unbalanced fuel flow into the 6 cylinders. The imbalanced fuel flow caused the slight vibration. Yes, it was nearly imperceptible, but it was there.

Within a day or so the shop installed an overhauled unit and returned the Bonanza back to service. A short post-maintenance flight confirmed the diagnosis, and the vibrations were completely gone.

One of the advantages of flying your own plane is that you learn every sound, feel, smell and nuance of that particular aircraft. If something is not quite right, you have an instinctive feel for it.

Aircraft renters typically fly many different models from the FBO’s rental fleet, and never really get to know each aircraft so intimately. As a result, they might miss signals that all is not quite right under the hood.

Just like spouses, horses and Golden Retrievers, your plane will speak to you….but you must listen closely.

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