March 9, 2012
The trainer is cruising along as usual, but something isn’t quite right. The engine is smooth and gauges show no sign of trouble. A check for carburetor ice produces negative results. So what’s up?
The ignition switch catches your eye. You discover to your chagrin that you have been flying along on one magneto. A turn of the key to the “both” position and the normal sound of cruise—and about 50 rpm—quickly return.
You might ponder two lessons from this not-uncommon scenario: One is to pay better attention to detail when performing the pre-takeoff checklist, remembering to return the ignition switch to the “both” position after the mag check. The other is that it is safe to fly on one magneto if necessary. That’s what the dual-magneto ignition system that drives your trainer's engine was designed to make possible.
Redundancy builds a safety margin into aircraft operations. When you first began to study the pilot’s operating handbook for your aircraft, you learned that the battery and alternator provide electrical power for systems and instruments, and that engine ignition was a separate system energized by gear-driven magnetos mounted at the rear of the engine. Plus, there are two magnetos, each with its own wiring for the associated spark plugs in the engine cylinders.
During the pre-takeoff engine runup, you check the system by watching for an rpm drop as specified by the aircraft manufacturer for when one mag is operating. “Too great a drop in rpm can be an indication of several problems—anything from a fouled plug to a bad ignition wire to improper timing to a bad magneto. It needs to be checked by a mechanic,” explains the Flight Training article “The magneto check: What are you looking for?”
No rpm drop? That’s also a sign of trouble requiring attention from the maintenance team before the aircraft flies again.
An engine that suddenly begins to run roughly in flight despite being leaned properly and free of carburetor ice could be experiencing a malfunctioning magneto.
Check each in turn: Roughness while running on one, and smooth operation on the other, helps isolate a diagnosis. Remain on the good magneto and return for a normal landing, knowing that a safety-minded design is working as it should.
Former CFI of the year and Gold Seal flight instructor Rich Stowell shares some knowledge from his extensive aviation career on an audio CD. The 16 audio tips touch on subjects ranging from human factors, the fundamentals of aircraft control, and flying in the traffic pattern. The CD is $9.99 and is available from PilotMall.com.
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Question: What is the purpose of a soft-field landing?
Answer: The purpose of a soft-field landing is to have the wings support the weight of the airplane for as long as practical in order to minimize friction and stress on the landing gear. You will want to utilize this technique when landing on a surface like a grass-, gravel-, or snow-covered runway. Be sure to check your airplane’s flight manual or operating handbook for specific procedures on how a soft-field landing should be performed. For additional information on soft-field landing technique and what to expect on your checkride, visit AOPA Online.
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