Aircraft engines. You can't live with 'em, and you can't live without 'em if you fly airplanes. Engines are necessary, but cantankerous and expensive. They're costly to buy, they eat constantly, and they're maintenance-intensive compared to the rest of the airplane. These money machines have a direct influence on our financial and physical health and well-being, so we like to keep a close eye on their health and well-being. That's the short version of why aircraft owners install engine-monitoring systems.
My partner and I got one for our airplane. It's a JPI EDM-760 (for piston twins), and like most such microprocessor-controlled engine monitoring systems on the market, it tells us more than we've ever known about how our engines are feeling and performing on each flight.
The device monitors and displays — in both digital bar graphs and numeric readouts — exhaust gas temperature, cylinder head temperature, peak exhaust gas temperature, oil temperature, battery voltage, cooling rate, the temperature difference between the hottest and coolest cylinders, fuel flow, fuel used, fuel remaining, time until empty tanks, and outside air temperature. There's no substitute for facts when it comes to figuring out what's happening just behind the props, and modern engine-monitoring systems certainly do give you lots and lots of facts.
That stack of facts enables me to fine-tune power settings to achieve whichever performance goals I desire, and also to detect and troubleshoot engine problems the moment that they occur. Given that an aircraft engine spends money whenever it's running and spends even more when it's not running correctly, I've taken to calling our EDM-760 a cash-flow monitor. On a recent trip it proved its worth once again by detecting a potentially serious cash flow problem in the right engine.
I launched from southern Florida in the morning for the Washington, D.C., area with a planned early stop in Gainesville, Florida. My intent was to have a birthday breakfast with middle son Ian, a freshman at the University of Florida.
About 30 minutes into the flight, just south of the Lakeland, Florida, VOR, I glanced at the EDM display and saw that the EGT indication for the number-three cylinder on the right engine was out of kilter. The EGT bar graph was abnormally high, a sign that one plug in the cylinder was not firing. I fiddled with the mixture, hoping to clear a fouled plug, but to no effect. When I switched off the left mag, the engine ran rough. That confirmed the problem was in the right ignition system — but was it a bad spark plug, a faulty spark plug wire or connection, or a problem in the right magneto affecting the number-three cylinder? I hadn't a clue.
What to do? With both mag switches on, the engine ran smoothly enough, but the EDM display continued to note a pesky problem in the right number three. I could continue to Gainesville and simply hope that the problem would fix itself. But if it didn't — and I knew it wouldn't — I'd have to hope that someone in Gainesville could attend to the problem, or leave the airplane and try to catch an expensive airline flight to Washington. Neither option was desirable.
Then I realized that Piper Twin Comanche specialist Bill Turley was a mere 15 miles off my right wing, in Bartow, Florida. I requested and received a change in destination to BOW, and 30 minutes later Turley was pulling the cowls off the right engine. After running various troubleshooting checks, he identified the problem: the spark for the number-three plug was shorting inside the right mag because of a tiny crack in the distributor block.
Turley had one of his mechanics rebuild the mag with a new distributor block and new points, and that afternoon I was on my way again. The bar graphs and numerical readouts for each of the cylinders were reassuringly even and stable. Like those beeping electronic monitors attached to hospital post-op patients, the EDM display confirmed that the sickly right engine was once again well.
The delay forced me to skip my stop in Gainesville, so on the long flight to Washington I had plenty of time to think about the events of the day. When the ignition problem occurred, it caused the EDM to display an abnormally high EGT reading in one cylinder. That was a symptom of a problem, but I didn't know precisely what the problem was or how to cure it.
I was somewhere over North Carolina when I finally made the connection between engine monitors and money. When the display posts an abnormal reading, it means only one thing — you haven't been spending enough on the engine. Cash flow has fallen below the minimum required. The height of the bar graph is inversely proportional to the extent of cash flow — the taller the bar graph, the lower the cash flow. If that bar graph shoots to the top, plan to spend a lot to restore equilibrium.
That was true for my partner and me. We'd been doing a good job of not spending a lot of money on the engines. We've done most of the work — oil changes as well as tending to unanticipated problems, including a couple of bad spark plug leads and an oil leak — under the supervision of an A&P/IA. Because we supply the manual labor, engine maintenance costs have been relatively low.
Too low, apparently. Thus the too-tall bar graph south of Lakeland. Once I paid Turley, order returned to the EDM display. It seems pretty straightforward to me — an out-of-whack engine indication means you've got a problem that only money can fix.
