Aviation Safety Corner
GREETINGS! For this month's topic, I would like to continue discussing "Anatomy of an Engine Failure."
Examining the nature of power losses on takeoff and how they can be avoided. This is Part III of IV.
Let's begin our discussion with, "Avoiding Missed Beats." Normally, takeoff and initial climb are among the easiest maneuvers for the pilot; but they are the most difficult for the engine. You are asking your engine to go from idle to full power in a few seconds and expecting it to accelerate you to flying speed in the shortest possible time, all without missing a beat.
The engine is, of course, designed to give this performance if it is fed and maintained properly. Let's look at just what that means. A lengthy discussion with the chief engineer at Lycoming, Rick Moffett, revealed several things that can be done to reduce the possibility of engine failure on takeoff (or any other phase of flight, for that matter).
Keep your engine oil clean. Gums, acids and lead sludge that form in the oil cannot be removed by the filter, and they cause sticking valves. The only sure way to get rid of contaminants is to follow the recommended oil-change schedule. Typically, oil with screen filtration should be changed every 25 hours (every 50 hours with full-flow filtering) or every four months, whichever comes first. Check your operator's manual, and follow the manufacturer's recommendations.
Never use automotive oils or oils with automotive additives. Air-cooled aircraft engines have significantly different lubrication needs than automotive engines. They get operated less frequently, get exposed to different loads and temperatures, and require oil specifically designed for this operating environment.
Avoid automotive fuels. Primarily, aviation fuels meet across-the-country "uniformity-in-product" standards set by Uncle Sam. Automotive fuels are governed by state standards, which may vary a lot. Automotive fuels deteriorate more rapidly than aviation fuels (avgas is designed to sit two years in your tanks without loss of quality, though it's not recommended). Those who insist on using auto fuels should follow the STC provisions precisely.
Avoid sudden changes in power. Yanking the throttle back from max power places undue loads on the crankshaft rods, etc. It has been found to cause failures in counterweighted engines. Ease in the throttle on takeoff and ease it out during your power reductions.
Avoid shock-cooling your engine. Another consequence of quick power changes is to heat/cool those portions of the engine that cool rapidly, especially in colder temperatures. Shock-cooling is a major contributor to cylinder failures.
Put your engine on an oil-analysis program. It has been proven that oil analysis can find problems within the crankcase long before they become major.
Fly your engine. An engine that is not used is getting almost as much damage done to it as one that is operated improperly. Atmospheric moisture corrodes magneto components and creates bearing-etching acids in your oil. Moisture rusts cylinders, which may make your piston rings take a set on the cylinder wall. Extended ground runs may get your oil warm, but the inadequate cooling may damage the very components you want to save.
Only flight operation can get temperatures up to levels that can rid the oil of moisture-induced contaminants while assuring proper cooling. Optimum engine life can be reached at 15 or more hours per month of operation, according to Lycoming.
Now, Let's Discuss, "Harbingers of Trouble." Often, and engine will provide some sign of an imminent problem. Here's what to look for:
Abnormally rough running immediately after start. An engine that rattles and shakes for even a few seconds after start and then smoothes out may have sticking valves. The valve guides should be inspected for proper clearances and reamed, if necessary.
Oil in the exhaust pipe. Especially true of turbocharged aircraft, oil in the tailpipe is indicative of something not sealing properly. On turbos, oil in this area can mean real trouble.
Soot in the exhaust pipe. Black soot deposits indicate rich operation, which leads to excessive oil contamination, fouled plugs, preignition and detonation, and poorer lubrication of cylinder walls. Properly operated engines should have exhaust stacks that are a light powder gray or tan.
Intermittent abnormalities in operation. Problems that "come and go" or that frequently require a full-power run-up to clear are definite indications that something is wrong. If necessary, take your mechanic along and show what's happening (mechanics are far more attentive when they are riding behind the problem).
Oil anywhere but in the crankcase. With the exception of oil loss through the breather during radical maneuvering, oil should remain in the crankcase during normal operations. Evidence of leakage may indicate a loose attachment, a bad gasket, a blocked breather or deteriorated oil lines or fittings.
Excessive oil consumption. Oil consumption in excess of that advised as normal by the manufacturer for your particular engine indicates you've got a problem. A jump in consumption over a 25-hour period, too, may indicate something is going wrong. Consult a competent mechanic for advice.
Now, In Conclusion, Remember make sure the people who work on your airplane are competent. Many of the takeoff accidents in our sample resulted from problems caused by the mechanics' carelessness. It's in your best interest to screen the individual you're depending on to help keep your aircraft airworthy.
Don't miss next month's, Aviation Safety Corner, when we'll finish our discussion on, "Anatomy of an Engine Failure." Our Topics will be, "Preflight Strategies." And "Before-Takeoff Tips." This will be Part IV of IV.
Larry G. Harmon
FAA Aviation Safety Counselor