Helping Your Mechanic Diagnose Engine Problems

Many pilots and owners can greatly reduce their engine maintenance costs by doing a little record keeping after a non emergency in flight engine problem has arisen. A very observant pilot that WRITES DOWN HIS OBSERVATIONS can help a maintenance technician isolate and repair an otherwise elusive problem.

Many times in my career, I have had in-flight engine problems described to me in the most unbelievably general terms. An example would be a pilot report that "the left engine surges in cruise". I would ask "how much"? The answer "a little". I would ask "does it break sync, or sound funny"? The answer "I don't know, I'm not sure". I'll ask "What about the gauges, anything out of the ordinary happening there"? The answer, with a puzzled face "They were all in the green...... I think". Responses and information like this are of little help to a technician who is trying to figure out if he has an engine problem, a propeller problem or a propeller governor problem that may be causing the surge.

Here are some things to CHECK AND RECORD that may be of great help to a trouble-shooting technician. Being as specific as possible will further help the technician diagnose the problem.

  1. Scan every engine gauge and note all current readings for the problem engine as well as the good one. Note if any readings are different from the readings that were present earlier in the flight when everything was normal before the problem occurred. Note if any readings are fluctuating beyond what you normally see.

  2. Do an in-flight magneto check. Is the engine any rougher on one mag or the other? Does the engine perform more normally on one mag or the other, as compared to when both mags were selected.

  3. Does changing the mixture setting effect the problem? If so how? Does the movement of the mixture control produce results on the engine gauges that you are accustomed to seeing?

  4. Does changing the R.P.M. setting up or down affect the problem? If so how?

  5. Does application of alternate air effect the problem? If so how?

  6. Does varying the manifold pressure setting up or down have any effect on the problem? If so what?

  7. Does changing the airspeed of the aircraft by varying the angle of attack effect the problem? If so how?

  8. Does the engine sound the way it normally does ? What's different?

  9. Are the engine controls in the same position relative to each other as they normally are for the same power setting? If different, note the differences.

  10. Are the flight characteristics of the aircraft different from normal? (i.e. yawing, slow, lack of performance in climb) If so what's different?

  11. Are any warning or inoperative warning lights illuminated? If so which ones?

Obviously it would be impossible for me to list every observation that should be made to cover every possible problem, but answering the above questions will provide the technician working on your engine the answers to questions he must have answered in order to fix it. If you provide these answers in a clear and concise written report, he won't have to try and get the answers on his own, either by having a test flight performed or by performing ground runs, that may or may not show an in-flight problem.

Having a written report of conditions when the problem existed will also help greatly with intermittent faults that always seem to be non existent when a technician is checking for them.

Trouble shooting and test flying an aircraft can take a lot of time. Time relates to money whether it is in the form of payment to a technician or test pilot, payment for fuel and aircraft flight time to perform the tests, lost revenue, or just plain loss of use of the aircraft. You can help your wallet as well as your mechanic out by taking the time to carefully make and record what's happening when a non emergency in-flight problem arises.

by Mahlon Russell

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© Mahlon Russell 1998