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Did'ja Lean It Ouut?

Among aviation's many trite aphorisms, there is one that I consider forever immunized against the discrediting stigma of banality, and it is the one that, paraphrased, advises the following: 'It is always better to be on the ground, wishing that you were in the air, than it is to be up there and wishing you could be on the ground.' However, in the case of magnetos, as I learned one IMC day almost a dozen years ago, it is possible to be benched before you ever get the chance to engage in such battles of conscience. And it is also just as possible, and quite simple really, to get back in the game. It is a lesson that I learned too late that day, but none too late to share.Among aviation's many trite aphorisms, there is one that I consider forever immunized against the discrediting stigma of banality, and it is the one that, paraphrased, advises the following: 'It is always better to be on the ground, wishing that you were in the air, than it is to be up there and wishing you could be on the ground.' However, in the case of magnetos, as I learned one IMC day almost a dozen years ago, it is possible to be benched before you ever get the chance to engage in such battles of conscience. And it is also just as possible, and quite simple really, to get back in the game. It is a lesson that I learned too late that day, but none too late to share.

It was the spring of 1993. I was working at a telecommunications firm in northern Virginia, and I was all set to fly up to the annual Space Surveillance Workshop put on by MIT Lincoln Labs. My destination airport was Hanscom Field, west of Boston in Bedford Massachusetts, which was also quite conveniently the location for the conference. The present as well as forecast weather was for widespread IMC, although ceilings were not expected to go below 500 feet. My reservations were made, expenses pre-approved, my work was cleared up for several days, and everyone knew where I was going to be for a while, as of three hours from now. I had just gotten my instrument rating the previous summer, and I was current, and the airplane was ostensibly just as well prepared as I. It was packed, pre-flighted, I'd been issued a clearance for my IFR flight, and all I had to do was complete the run-up. I'd be remiss if I didn't also add that I was really looking forward to making this flight, and attending the conference.

First, a bit of Devil's advocacy: Abiding by such cautious wisdom is actually quite a leap for me, because when I'm on the ground, I have another alternate guiding life principle which is by implication the very inverse of the first: 'fortune favors the audacious.' For those of us who fly however, I think it good to be a bit schizophrenic in compartmentalizing where and when to personify bold behavior. Although I cannot pin down any baptismal ordeals after which I saw the light, for the last several years I've had little trouble dropping whatever commitments and accepting whatever logistical penalties may ensue, whenever things don't feel right. Just this morning I was not one block from my home, beginning the drive to the airport for a short local flight with my brother who is visiting from Pennsylvania, with an IFR flight plan filed and the briefer's blessing for safe flying conditions…that is, until mid-afternoon, when the cold front moving rapidly eastward through western New York, Pennsylvania, and the southern Appalachians was expected to bring lowering ceilings, near-zero temperature-dew point spreads, and light rain and snow showers. So there I was, in my car (to use a familiar phrase in a more mundane setting), when I began to notice drizzle on the windshield. It took me about two seconds to realize that this could become freezing drizzle aloft, and to decide that our entire outing today would comprise driving around the block and back into the garage. (I must also add that my brother is not a pilot, and this isn't the kind of day to take a non-pilot for a joyride.) I've written before about how easily one should be able to say 'to heck with this!' and can a flight. Now, that moralistic bit of disclaimer aside, here instead is a situation when a simple (but still very serious) thing like below-par engine performance during your pre-takeoff check can sideline your plans. And here is a possible path to a favorable resolution. You may not always win, but at least there's a chance.

Now back to the run-up area. I wheeled around to face the base and final legs, mostly into the wind and positioned to direct the prodigious blast from the Cessna 182's mighty Continental O-470 harmlessly away from other aircraft, applied the brakes, and throttled up the engine to 1700 rpm. I quickly switched the ignition from the 'both' position two clicks over to the right magneto, and observed an rpm drop of somewhere between 75 and 100 rpm, nodded approvingly to myself, and then switched back to both. Then it was over to the left mag, at which point the drop was…several hundred rpm. My heart sank, along with the rpm. I remember shrugging to myself, thinking about all those plans and wouldn't they be surprised to see me back at work later this morning. (The 12-hour drive was an option, but not one I cared to exercise.) So I taxied back to the tie-down spot, un-did all my packing, buttoned up the airplane, wrote a note in the squawk pages of the airplane's logbook and made a note to call the crew chief the moment I got back to my office. As I was driving back into the parking area from the 'airplane' side of the airport I passed our resident designated examiner, Bob Gawler, and told him what had just happened with our flying club's 182. (He was and still is also a member.) I can to this day remember his immediate question, just as he asked it in his touch of a Canadian accent: 'Did'ja lean it ouut?'

Well, uh, no, I hadn't, as a matter of fact. I hadn't known about leaning out a rough-running engine to improve engine performance to airworthy status. Rest assured that I've since learned. Here's the run-down on improving your chances of a successful run-up. If the power drop exceeds allowable limits, it isn't necessarily a bad mag. The problem could simply be that the plugs are fouled, either by oil or by deposits of lead. (If you're lucky enough to have temperature readouts for each engine cylinder, you'll even be able to identify the culprit; the cylinder with the fouled plug will be much cooler than the others.)

It's important to mention at this point that proper engine maintenance (including regular plug cleaning, gapping, and rotating), as well as correct engine operating technique (such as proper leaning procedures, as well as the smooth application of takeoff power) will go a long way towards preventing fouled plugs. But if you still someday find that your best-laid plans are 'gang aft a-gley', as Robert Burns put it, here is something you might wish to note for future reference:

  • First, don't reduce power to idle; leave the engine rpm up to run-up levels, and better still, higher (say, 2200 or even 2400).

  • Turn the ignition switch back so the engine is running on 'both' magnetos. Returning the mag switch to the 'both' position is important, because if you don't, you might not be able to generate enough heat to clear a plug (in whichever cylinder is falling behind) and burn off the oil or carbon deposits. (Since each cylinder has two spark plugs, you must be using one to help the other.)

  • Then slowly and carefully lean the mixture, just as you would in cruise flight. If you have an exhaust gas temperature gauge, lean the mixture until the EGT peaks. (If you don't have an EGT gauge, simply lean the mixture until the engine begins to run rough, and then enrich it just enough for the engine to return to running smoothly.) This will possibly burn out the excess oil or carbon deposits. You need some patience and a bit of discipline here to run the engine hard and lean, and for as long as a full two minutes, unless the cylinder head temperatures or other engine indications exceed tolerances. (Lead deposits probably won't go away with the application of power, however.)

  • Then return the mixture to the normal takeoff position (usually full rich) and try again. Then if the engine is still running poorly, you'll fly again another day. Just not today.


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