Living Vicariously—and Safely

“That’s what I would have seen if I had followed Jim’s suggestion to look directly into the throttle body.” Philippe DeKemmeter

Santa Paula Airport is a 20-minute flight from my home base, Whiteman Airport. The fuel there is $1.25 per gallon cheaper, however, so when I’m flying around the local area, I often stop at Santa Paula to refuel. The precise economics of fuel tourism are an SAT-level problem, but if I’m over Santa Paula anyway, I figure the extra landing and takeoff can’t cost me more than 10 bucks.

Turns out, I’m not the only cheapskate. The other day, as I was finishing fueling, a Cessna 180 rolled up to the other pump. The pilot—I’ll call him Jim—came over to chat, and it turned out he was based at Whiteman too, a couple of hangar rows over from me, and was here for the same reason I was.

When I started up to fly home, something unexpected happened. I pulled the throttle back to idle, but the engine kept running at high power. I shut it down immediately. Jim came over to see what was wrong.

After repositioning my plane so it was no longer pointing directly at his, I tried again. Same thing.

I opened the cowl and inspected the throttle linkage there and in the cockpit. All secure. Head scratching time. Jim watched the throttle butterfly shaft as I moved the cockpit lever back and forth; it was turning. He got on the phone and returned a minute later with the suggestion that an intake leak could produce this effect.

I was skeptical. I didn’t see how an intake leak could produce 1,700 rpm with the throttle at idle. Nevertheless, I took off the rest of the cowling and carefully inspected all of the joints in the induction system. No leaks.

Jim suggested I remove the connection where the duct from the turbocharger meets the throttle body, so I could see for certain whether the butterfly was rotating properly. That was good advice, but I didn’t follow it because I believed that if the visible end of the shaft was turning, the butterfly and fuel-metering orifice—which is at the other end of the same shaft—must be doing the same.

I phoned an A&P at the other side of the field and described the problem. He said he’d come over and have a look—I love the easygoing friendliness of little airports—and a few minutes later, he rolled up. It didn’t take him long to notice that, although the butterfly shaft was indeed turning with throttle-lever movement, it wasn’t keeping pace with it. It was slipping. That’s what I would have seen if I had followed Jim’s suggestion to look directly into the throttle body.

The peccant lock nut was tightened, the cowling replaced, and I was on my way.

Reflecting on this minor event afterward, I realized it had not been completely unheralded; I had merely ignored the herald. For an indefinite period of time—months, certainly, perhaps grading into a year or more—I had noticed when I was taxiing and wanted to increase the rpm a bit, the engine’s response was sluggish. I had to move the throttle lever half an inch or so before the engine gave much of a response. I attributed this hysteresis—which developed so gradually, I was uncertain it had not always been there—to my somewhat unconventional turbo controller, a manually adjustable variation upon the TSIO-360 fixed wastegate used in many airplanes. The internal diameter of the bypass duct is only three-quarters of an inch, so even when the wastegate is wide open, the turbo is still bootstrapping a bit.

Read More from Peter Garrison: Technicalities and Aftermath

I did not have a well-thought-out theory of just why this wastegate design should lead to throttle lag. The explanation was just an evasion, a convenient cupboard, so to speak, in which to keep an unsolved mystery out of sight. I made a mental note: There is a tendency in the human mind—assuming my particular mind is representative of the general—to relieve anxiety by rationalizing what is not clearly understood. Thus, having invented a plausible-sounding explanation for slow throttle response, I had ceased to ask myself, “Can there be something wrong?”

Another aspect of the incident gave me a certain gratification. Years ago, a friend told me about the time the throttle cable on his Bonanza had become disconnected from the engine in flight, leaving it at full throttle. My first reaction was that this would have been a disconcerting emergency, and I wasn’t sure how I would have dealt with it. During 55 years of flying, I’ve had some pretty stupid reactions to emergencies.

My friend said, however, that he had landed without incident, using the mixture to control power.

The moment I started my engine at Santa Paula and it began running at high power, the recollection of my friend’s story was there. My hand went straight to the mixture vernier. Of course, it would have gone there eventually anyway. How else are you going to shut down a runaway engine? But what struck me was the feeling of familiarity I had and the unflustered immediacy of my reaction. It was as if I had been there before. And, in a sense, I had.

Which brings me to Aftermath.

I haven’t seen the statistics in recent years, but the Aftermath column—which I have been writing since before some of our readers were born—at least used to be one of Flying’s most-read columns. I would like to imagine that its popularity was due to my elegant prose style, but other factors—malicious enjoyment of the misfortunes of others, the agreeable thrill of participating in an adventure without suffering its consequences, and the pleasure of thinking what an idiot somebody else was—probably had more to do with it.

Pilots have no trouble understanding why narratives of accidents are interesting, but nonpilots sometimes do, and from time to time, I would find myself expounding the higher purpose of my macabre-seeming columns.

I would explain that, as I imagined it, Aftermath had two aspects. One was the “There but for the grace” side. Pilots would remember having been in similar situations, and the fatal outcomes would remind them things could have gone differently than they did.

The other aspect was that I hoped—by describing in detail the events leading up to accidents, and attempting to get inside the ill-fated pilots’ heads and see the circumstances as they may have seen them—I might create the same kind of vicarious experience as my friend’s loose throttle had in me. If one pilot, approaching an area of low ceilings between him and a tantalizingly nearby destination, or making a third try at an approach to minimums, felt that there was something familiar about the situation—without necessarily realizing it was familiar because he had read about it in Aftermath—and, as a result, made the more cautious of competing choices, then the column would have served its purpose.

Peter Garrison taught himself to use a slide rule and tin snips, built an airplane in his backyard, and flew it to Japan. He began contributing to FLYING in 1968, and he continues to share his columns, "Technicalities" and "Aftermath," with FLYING readers.

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