Prospecting for oil

August 1, 1997

General aviation aircraft are so reliable that hundreds or even thousands of preflights seldom turn up a mechanical find that justifies the effort of the ritual. How often have you looked expectantly for the oil leak, the cracked hose, or the broken wiring, only to be perennially disappointed? Sooner or later, however, there will be a payoff.

This flight was a southbound trip in a Beech A36 Bonanza to Jacksonville, Florida. The plan was to refuel in Florence, South Carolina, and proceed. Florence is one of those small-town airports that has all the facilities without the delays of the larger burgs. The FBO, Carolina Air Service, flagged us into a parking spot, and the fuel truck was there almost before the prop stopped. There was just time for a stretch, a soda pop, and payment of the bill before returning to the aircraft. It was the perfect quick turn — elapsed ground time about 15 minutes.

Some background will put into context what happened next. The Bonanza had just returned from a major engine overhaul a week before. This was one of those spectacular blueprinted jobs from which the engine comes back reborn with all-new everything, balanced and ported, painted, polished, chromed, buffed, and — well, just about perfect. Just about. The aircraft had suffered an oil leak before delivery, and the overhauler had tended to that immediately. Since then there had been a half-continent cross-country trip and several shorter flights. I had flown the aircraft for several hours on the day before the Florida trip. Total engine time was about 26 hours, and oil consumption had stabilized. It hadn't burned a drop in 8 hours. The engine was purring, and while I can't be sure, it seemed that the Bonanza was at least 5 knots faster than previously remembered. This freshly overhauled engine business is a powerful elixir.

For most pilots the first inspection of the day is the most rigorous. We look for new dents, birds' nests, and damage from the previous flight, and we check the aircraft's critical fluids. I am usually more confident on the day's subsequent flights because by then I've spent recent time with the machine. Like some people, airplanes occasionally wake up crabby but are happier later in the day after they have been flown.

During the Florence quick turn I had observed the fueling from the door of the FBO and ensured that it was the avgas truck and not the Jet-A truck that pulled up. It is always good form to check that you got what you paid for in both quantity and quality. The lineman had done the job to perfection, the caps were on tight, there was no water in the fuel and, well, perhaps it would be a good idea to admire the engine just one more time before we launched. I have to admit that, on occasion and with a familiar aircraft, I haven't always checked the oil on a quick turn. There are several reasons. The oil readings are likely to be inaccurate because much of the oil is still dispersed throughout the engine; the dipstick is usually too hot to handle, and it takes more time. The old-timers already know where this is headed.

One should always look at the ground beneath an aircraft — not to worship but to look for drippings of the aforementioned critical fluids. There was just one drop of fresh oil adhering to an antenna. The belly had a slight film of oil, but what airplane doesn't? Some of the poor old rental wrecks that we've all flown on occasion are held together by encrusted belly oil. Here's where the familiarity pays off — this airplane is usually pretty clean. When I opened the cowl there was a massive amount of oil on the keel that supports the engine. The previously pristine engine compartment was now awash in the finest of lubricants. Jackpot! After years of preflight inspections, prospecting for oil had finally paid off — in spades.

The inconvenience that followed was meaningful. It was Sunday afternoon in Florence. Who you gonna call? Not Ghostbusters. But the head mechanic arrived within the hour after being summoned from Sunday's pleasures. The remainder of the afternoon was spent looking for the leak, which, despite significant quantity, was not immediately apparent. Eventually we traced it to the tachometer generator accessory case. This was the part that had leaked before delivery.

I came away with several observations. Engines should be painted a light color so that oil leaks stand out better. While this engine is an aesthetic tour de force, the beautiful dark paint on the engine block and accessory case made it more difficult to spot the source of the leak.

Beech is to be commended for putting a big, easy-opening cowl on the Bonanza, allowing a quick and detailed inspection. The tiny oil access doors that grace many aircraft cowlings would not have facilitated a quick discovery of the leak because it was in the lower part of the engine. Peering through a 4-inch-diameter cover may be expedient to quick preflights and inexpensive construction but it doesn't help pilots in their efforts to be thorough. The cowling design also saved considerable time for the mechanic to get into the problem. There are cost issues and design considerations, but after this experience, I'm a believer that more access is better, a lot better.

An engine compartment check at each stop should be a part of the discipline of preflight, and while you may go unrewarded for a hundred or even several hundred flights, when the reward comes, it will be worth it. In a similar vein, how many pilots skip the magneto check during an en route stop — reasoning that if it flew in, it will probably fly out? A broken wire on the spark plug wiring harness years ago reinforced my thoughts on the value of anticipating failure and checking the mags every time. Hasn't happened since, but these things do take time to develop.

Back to the leak. After 3 hours and four engine runups to test the inexpensive fixes, it was obvious that the tach drive case on the back of the engine would have to come off. To make a long story slightly longer, we spent the night in Florence and made some new friends, including a VFR Canadian pilot who had the good sense to wait out some weather that was delaying his trip. We exchanged stories and enjoyed the camaraderie of a fellow pilot who was just as anxious to get to his destination as we were to reach ours.

At 8 o'clock the next morning, the mechanic started to remove the tach drive housing, which is in an ugly spot on the back of the engine. I was truly impressed with his patience, his dexterity, and the amazing conglomeration of tools that it took to get the cover off. The technicians who keep us mechanically sound are the saints of the business. After 6 hours and some very delicate handling, the tach drive was reassembled.

The epilogue to the story was a successful test flight, and the remainder of the trip was uneventful. Oil on engines is much like blood — it doesn't take much to look like a lot. After all the mess, the big Continental had lost only about half a quart, but that could have taken place over 3 hours or during the last 5 minutes while taxiing in. Like blood, oil is much better when contained in the proper vessel.

Cleanliness on engines and the undersides of aircraft is essential to spotting problems early, so if that's a mandate to get out the brush and solvent, go do it or have it done by someone who knows what he's doing. Finally, keep on prospecting for oil around airplanes. It can be a very profitable activity.


See also the index of "Safety Pilot" articles, organized by subject. Bruce Landsberg is executive director of the AOPA Air Safety Foundation.