That’s the mantra of every flight instructor—scan, scan, scan the instrument panel, checking each gauge on each scan. But what are you looking for?
Are you really checking the oil temperature in degrees, the manifold pressure in pounds or the electrical gauge in amps? Probably not. But then what are you checking? As is typical, an old CFI straightened me out on that subject. “What you look for” he said, “is change.” That bit of advice has served me well over the years.
Simply put, the old pro was telling me to look for any change in any and all gauges. Every change, he told me, means something. That’s why you scan the gauges—to see if any of them has changed. If something changed, you need to find out why. Then, if the change is caused by a problem, you decide how to solve it.
Say you have been steadily cruising for awhile when your scan shows that the oil temperature has changed. What does that mean? It could be important. That happened to me less than an hour after I picked up a brand new Aztec at the Piper factory. I landed at the next airport, and a tech and I looked for problems under the cowl. Finding none, and remembering that after I first noticed the temp change the gauge had held steady without further change, I flew the Aztec back to the factory. Turned out the problem was minor. A burr under a valve kept the oil from flowing through the oil cooler. Piper fixed it and I flew home peacefully.
Another time, in a brand new Piper Tomahawk—the first one I had ever flown—the oil temp changed rather dramatically. That time the problem was electrical and, again, the fix was quick and easy.
The big question, of course, is how do you spot changes during your scans? That old pro provided the secret to that, too.
He said, “Don’t look for degrees of temperature or inches of pressure.” Instead, he said, notice and remember where the needle was pointed when everything was normal. The oil temperature gauge might normally sit on the letter “i” in the word “Oil” on the gauge. If your scan shows it has moved to the letter “T” in “temperature,” sit up and pay attention. Same goes for the oil pressure gauge. You will notice such changes faster this way than if you are looking for changes of a few degrees.
How to remedy the problem comes down to training and problem solving. Ask a CFI what you should do if this gauge changes one way or that gauge changes another way. For one example, if the oil temp changes (up or down) you should quickly check for change in the oil pressure gauge.
Recently I was a passenger in a rental airplane that normally and regularly showed a temp that was way too high. The owner explained that the gauge was wrong, that it always stayed that high. I was not comfortable with that. After all, how would you tell if the oil temp changed?
Try this. I bet you’ll like it.