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Do You Use Your Checklists?

Are you checking your mags?

By Lee Taylor, EAA 519694, tdpilot@gmail.com


Recently at one of our local fields, one of our best (and most experienced) mechanics was finishing up the annual inspection on a 1999 Cessna 172. He was almost finished with the checks, and with this new of a plane and with a conscientious owner, there wasn’t much that actually needed to be done.

I'm not exactly sure what repairs or maintenance was done, but it did involve some work around the propeller, and rotating the prop by hand. The mechanic and his helper, another aircraft inspector, had both done everything they had thought necessary to ensure safety while working around the prop, including checking that the mags were switched off and the key removed, that the mixture was in idle cutoff, throttle set to full idle, and that the plane was chocked, etc, etc.

But apparently, it wasn’t enough. Another helper, who was there at the time of the incident, said, “I was standing out at the wingtip and saw my boss move the prop. I heard the mag impulse coupling clickand immediately heard a pop. The next thing I knew, my boss was pitching backwards and landed full force with his head thudding against the concrete floor.”

My friend had, for the very first time in his lifelong career, moved a prop while being under it. When the impulse coupling clicked, a little fuel remaining in one cylinder fired, just a single pop, and the swinging metal prop hit him right square in the top of his head.

Before going any further, let me say that all of us are so incredibly grateful for the outcome (things could have easily been far worse) that we all went to church the next Sunday. He’s now walking around with this huge bandage on his head, as the prop split his scalp and fractured his skull, and has a severe concussion and another skull fracture from hitting the concrete floor. He has a perpetual headache for now, but he is, and will be, okay.

What the heck happened? Seemingly, he had done everything right, except for being under the prop as he moved it!

This relatively new airplane had a defective mag switch. Later testing determined that with the switch in the off position, jiggling the key could make the internal contacts open up, which causes a hot mag, even with the switch in off.

So What to Do?
A couple of the guys came to me and asked what in the world they could possibly do to avoid having something like this happen again. These are highly experienced pilots who have been around aviation all their lives and own their own planes, guys with long reputations for being safe individuals. One of them is the owner of the subject plane and a good lifelong friend of the injured mechanic.

I asked them, “Well, are you doing your complete shutdown checklist every time?” “Well, yeah, we always do,” they said. “What is your checklist?” I asked. “Do you check the mag switch before shutdown to see that it will kill the engine before pulling the mixture control to shut the engine down?” They responded, “What do you mean, ‘Check the mag switch’? After the engine dies, we turn the mag switch off and take out the key.”

Well, guys, that’s why this accident happened. A proper shutdown checklist wasn’t used. None of the several guys that eventually asked me were doing their shutdown checklists properly. None of them were checking the mag switch before shutdown.

At some point before the engine is shut down, the engine rpm should be set to the designated idle speed. Then the mag switch should be turned to the off position to make sure that the engine does in fact quit. Upon confirmation, the switch should be rapidly returned to the on position and the engine should restart. Once verified, the pilot can proceed with shutdown via mixture. This process absolutely ensures that turning the mag switch off does in fact ground out the mags. This is how the mags are disabled. If this grounding of the mags doesn’t occur (the switch is bad, or you have broken or disconnected P-lead), then the engine will not die! You have a hot mag, even though the switch is in the off position and the key is removed. In this case, moving the prop can be fatal.

For our friend, we’re so incredibly happy that it wasn’t in this instance.

May I be so bold as to present the shutdown checklist I was taught as a young kid – fifty years ago?

This is a generic checklist. It can be written down, but personally it’s one that is imprinted in my head as somewhat of a mnemonic device, but not as mnemonic as “ARROW” (more recently "AROW") or “GUMPS.” It has been usable on every single airplane I’ve ever had anything to do with, including the jet fighters I used to work on and occasionally fly.

It’s Shutdown Checklist – 1, 2, 3, 4, 5:
1. All avionics off
2. Engine shutdown
3. Electricals off
4. Mags off, key out and stored
5. Master switch off

  1. All avionics off
    Turning the avionics off before engine shutdown prevents them from potentially experiencing a voltage spike, but it’s far more important that the engine not be started with the avionics on. Shutting them off before shutting down helps ensure  they’re off before starting next time.

  2. Engine shutdown
    Use whatever procedures specified for your particular engine. On a mag-equipped engine:

    A. Idle power
    B. Mag switch to off (engine dies) and immediately back on to both.
    (Engine restarts before the prop stops.) This is the step that determines if the mag switch does in fact work, and our guys weren’t doing it! Had they done it, our friend might not be walking around now with that huge bandage on his head.
    C. Mixture control to full lean, engine dies.

  3. Electricals off
    Nav lights, fuel pumps, and anything else on an electrical switch. Verify that whatever the switches control do in fact terminate the operation.

    This check, in this order, also verifies that the proper solenoid functions properly, as the electrical energy keeps going after the engine shutdown until you turn off the electrical components. It also checks that the individual switches are functioning properly.

    Not the master switch. It stays on for a little longer; I’ll explain in a  minute.

  4. Mags off, key out and stored
    Please, guys, do not leave the key in the ignition, even though the switch is off.   I can tell you another horror story some other day.

  5. Master switch off
    Ensure that the battery isolation solenoid is functioning properly.
    Verify that the strobe lights have gone out.

Oh, I forgot to explain that one about the strobes, didn’t I? I mean, shouldn’t we have turned them off already in step three?

Actually, no.

I never turn my strobes off unless they’re going to blind someone. Why? It’s darn hard to walk away from your airplane, having forgotten to turn the master switch off, if the strobes are flashing at you, as if yelling, “Hey, dummy! Come back and turn the bloody master switch off!” And the strobes aren’t voltage-sensitive like the radios.

Guys, checklists are so incredibly important. Almost every single item on any checklist is there because it has been written in blood. That is, at some time in the past, blood was spilled and lives were lost because these checklist items didn’t exist beforehand.

It really doesn’t matter what kind of checklists they are, be they written, mnemonic, an electronic readout on your glass cockpit, whatever, but please, please use them. Religiously. I don’t want to see anymore of my friends walking around wearing bandages. Or filling holes in the ground. Or causing holes in the ground!

By the way, do you know how aviation checklists were started?

They all began because of an incident with the very first Boeing Model 299 (precursor to the B-17) public flight demonstration which occurred October 30, 1935.  

This was an extremely complex plane at the time and totally new in every way. And the pilots had pretty much taught themselves how to fly it, memorizing the critical preflight steps. This very first public demonstration flight was of course in front of every single bigwig in the world. To say it was stressful for the pilots and Boeing would be a slight understatement.

The airplane taxied out for takeoff, power was fully applied, and the plane started rolling down the runway for its first public takeoff. It lifted off and climbed normally but suddenly stalled, rolled over, and crashed. Two of the five aboard died from their injuries.

The pilots had forgotten to remove the elevator control locks. The plane was dubbed “too much plane for one man to fly,” but the reality was that it was simply too complex for any one man’s memory. Checklists were introduced immediately afterwards.

One of my first experiences with the need for checklists started very early, at age 13 after I got a job at the local airport.

You might remember that originally the Cessna 120s and early 140s used toggle switches for mag switches. And they all came from the factory “backwards.” That is, up was off (mags grounded), and down was on (mags hot). I learned all of my initial lessons this way. I’ve never figured out why the factory sent them out like this – it didn’t make sense. Further, my recently purchased 140 still has its switches this way.

At the time (1957), most people were flipping the system over so that the switches operated in a more “normal” way. All you had to do was loosen the switch locknut, rotate the switch 180 degrees, and retighten the locknut. Then up was hot, and down was off.

My boss had done this the month before my lesson but forgot to tell me! And since the plane had just landed from another student and therefore was still hot, he figured it would start right up. He called out to me, “Brakes and contact!” (We almost always hand-propped back then.)

I had checked the switches up on my preflight (actually had to move them up because the previous idiot had left them down/on!), so when my boss yelled, “Contact!” I naturally flipped the switches down (to what I thought was the on position) and waited for the start.

It didn’t happen. Of course, the mags were now off, grounded.

Mitch Bohamera (now deceased) cranked and cranked and cranked some more, with the throttle position all over the place, trying to find a “sweet spot.” Wasn't happening; engine wouldn’t even pop.
Mitch was now huffing and puffing like a spent racehorse (he was quite chunky and out of shape), totally worn out and breathless: “Ho-kay (pant pant pant), we must’ve flooded the cur.”

“Give me switches off, full throttle,” he said. I flipped the switches up – remember, originally up was off – and yelled back, “Switches off and full!” “Brakes!” he shouted, shoving on the nose to make sure I was holding them. (That was just plain common practice with us regardless of what we were doing. If the prop was to be moved, the plane had its brakes held, and/or it was tied down.)

Mitch was very tired, and now “since the mags were off,” just a little complacent. He planned on flipping the prop backwards several times (to clear out the flood), then going back to contact.
Since he wanted to clear out the “bad gas,” he propped it pretty hard. And the engine immediately fired – at full throttle!

You never saw a fat man stumble backwards and run so fast in your life!

I, of course, yanked the throttle off, but I couldn’t figure out how to shut the engine down! Remember this was before mixture control was used for shutdowns. And I knew I had the mag switches up, that is, off/grounded!
I was about ready to cry; I knew I had nearly killed my boss and good friend, and I was sure my days at the airport were over. Mitch, on the other hand, after he got up from resting on the grass a hundred yards away, was so incredibly embarrassed, remembering that he had neglected to tell me that the mag switches had been reversed.

Mitch claimed to have lost ten pounds – he ran so fast, hard, and far – after that engine almost ate him. We agreed that must have been the reason his pants were wet; they were wet “from the sweat,” and the brown stains were from where he had slipped in the mud puddle at the end of his run. Yep, that had to have been it.

I learned about mag safety and prop safety very, very early on. I don’t trust dem meat slicers. And there are funnier ways to get wet, brown-stained pants.

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