The downwind leg was progressing flawlessly. About halfway down, Michael started the before-landing checklist drill, "Safety belts and shoulder harnesses - fastened; fuel selector - both; mixture - rich...."
Just then, a large black bird swooped left to right across our windshield. I could hear our winged warrior's cry just inches from the cockpit.
My student's reaction was rock solid. Never a burble. The only problem was that the before-landing checklist had been interrupted or "broken," and the carburetor heat control knob never came out when it should have. I made a mental note to see how long after he reduced power it would take him to notice and correct his mistake.
"No big thing. Just a momentary distraction," I said to myself. But it got all of our attention for those few split seconds. An interruption in the before-landing routine. Downwind continued.
Ritually, the flaps went to 10 degrees abeam touchdown. He instinctively added just that little touch of nose-down trim needed to take pressure off of the obligatory forward stick application. Attitude was perfect. Altitude was perfect. "Hands off" again. "Hey, Michael is really getting good," I thought to myself with a certain degree of instructor's pride. After all, I'd taught him everything he knew, hadn't I? Nonetheless, I made a second mental note to see how long it would take him to apply the carb heat.
Approaching the 45-degree point, my prize student glanced over his left shoulder to check position, smoothly retarded the throttle to about 1,500 rpm, and gently banked into base leg as the nose of the Cessna 172 imperceptibly settled into about a 500-fpm descent. Really smooth.
Still no carb heat yet. I made yet a third mental note to critique him on that.
After a stabilized final approach and flare that was so smooth I just sat back in awe, he "painted it on" the centerline of the nontowered airport's runway.
He'd worked hard enough for the moment. Besides, I had a couple of words of constructive criticism to impart before I forgot them, so I said, "Relax, Michael. I've got the airplane. Now tell me what you forgot to do on that last pattern!" After the exchange of controls, flaps were cleaned up; throttle to full power; maintain centerline; glance at the elevator trim; check the tach - and we were back in the air.
Everything looked normal, or so I thought.
At about 200 feet above the trees, the sound of the engine changed and the airplane noticeably stopped accelerating.
I instinctively knew there was no way that I'd be able to make the clearing I knew was about a mile or so ahead of me and 30 degrees left of the nose.
As we descended at about five miles per hour below best glide speed (we had already decelerated to below best glide before I even recognized that something had happened), an alarm bell suddenly went off in my subconscious. I lowered the nose slightly, kept the wings level, and pulled the carburetor heat knob out so fast that I thought I would jerk the handle clear out of the instrument panel.
In what seemed like no more than a nanosecond, the engine roared back to life, and the airplane stopped descending.
End of story.
The Rest Of The Story
I had just experienced a case of "How stupid can you get?" I had committed the cardinal sin for CFIs. I had innocently allowed a student to get away with a major error without doing something about it immediately, and I never will again. And that's the moral of this story.
It's called "Doing it to yourself." We've all done it, or will. It's easy to do and even easier to repeat, if we don't learn from our mistakes.
I had just lived through one that almost got me. Shame on me! I was an experienced instructor with thousands of hours of flying time, and I should have known better - but I didn't at the time. Not only had I momentarily lowered my standards because the student was doing so well, but I also revealed a dark little corner of my knowledge - or lack of it - that almost put us in big trouble.
Has anything like this ever happened to you? If so, I hope you've sorted out what happened, why, and - most important - what you can do and could have done to prevent reoccurrence. In my case, I thought it was important to sort out how this happened and then do something about it.
What lessons could I learn from this experience? What could I pass on to others that would help them to avoid something like this?
One lesson I learned was that I really didn't understand carburetors or carburetor icing as well as I should have. Another, perhaps even more important lesson was how potentially costly it can be to lower your guard (or your standards) even slightly while you're giving instruction - or anytime in an airplane, for that matter.
So what did I do about it?
Three things: I established a policy of always researching or reviewing any system, regulation, technique, or procedure that gave me cause for concern or uncertainty during a particular flight as soon as possible after the flight or lesson was completed. I established a solid program to regularly review publications that would help me keep up to speed on things I needed to update and/or understand better. And I vowed never again to lower my standards.
I believe in flexible, "situational" flying and awareness, but not situational standards.
I even bought some basic texts, manuals, and other books that would allow me to research systems about which I thought my depth was too shallow. Ask yourself periodically - a particular flight, occurrence, or incident is my key - whether you really understand how system "x" or "y" works. If not, check it out. There are a lot of good references out there.
The carburetor heat problem (actually, it was my problem - not the carburetor's) actually led me to research FAA accident reports, check out a couple of systems books, and ultimately contact the British Civil Aviation Authority. That pointed me back to an AOPA Air Safety Foundation pamphlet on aircraft icing and a carburetor icing chart originally published by Canada's Ministry of Transport.
All this information taught me that carburetor icing can occur literally anytime an airplane flies, certainly up to at least 100.degrees Fahrenheit, even when there's not a cloud in the sky. The message is simple: For all practical purposes, use full carburetor heat anytime you retard the throttle significantly.
Air can be cooled as much as 70 degrees F just going through a carburetor's intake venturi. There are hundreds of carburetor icing accidents in the FAA's databases. The lesson: Use full carburetor heat.
The Real Lesson For Instructors
The real lesson I learned was to adopt high standards, maintain them, and never compromise. When the checklist says, "carburetor heat - on," that's what it means. Ignore checklist items at your peril. And that goes for every item on every checklist; every procedure in the Aeronautical Information Manual; every paragraph of every regulation; and every procedure in the flight manual.
We can't know them all, of course, but we and our students need to know what's in them all - or where to find what we need if we're unsure - and follow them faithfully.
The exception to that maxim occurs when emergency situations or common sense dictate otherwise. That's why the pilot in command has the authority to deviate from any provision of Part 91, for instance.
We owe it to our students to ensure that they pay attention to detail. That starts with taxiing on taxi lines. If our students don't taxi on painted taxi lines, how can they be expected to consistently land on a centerline? And if they don't do that, why should we expect them later on to fly the precise centerline of an ILS or VOR final approach course?
If they are not accustomed to touching down at a precise point on the runway - and doing it every time they are in the airplane - will they do it when they fly solo?
Part of our job is to help our students handle real-life flying and the problems that can result. They are human beings just like their instructors, so that means teaching them the tricks we've learned. One of those is the simple act of how to use a checklist.
If I had insisted that my student go back to the checklist once that behavior was "broken," carburetor heat would have been the next and last item on that checklist.
But too often, that's how it happens. Accidents are caused by omitting little things like carburetor heat from check-lists, aren't they? The reasons why don't matter. The fixes we CFIs implement to help our students avoid these occurrences do matter.
Wally Miller is president of an aviation training, consulting, and marketing firm in Monument, Colorado. He is a Gold Seal CFI who has been instructing for more than 30 years and flying for more than 40.
Related Articles
