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Don't worry, train happyDon't worry, train happy

If you had to guess, would you think that mechanical failures cause more, fewer, or the same number of accidents during training than on other types of flights? It’s not immediately obvious. Training aircraft suffer a lot of abuse, but they also get 100-hour inspections (at least if they’re rented). This ought to help catch discrepancies before they become real problems. An engine probably doesn’t know or care who’s running it, and flying frequently at least serves to minimize corrosion damage. You’d hope that a CFI would be in a better position to manage an in-flight emergency than the typical private pilot—but a student flying solo would not.

A word of clarification is probably in order. We’re not talking about all mechanical failures—a solid answer to that question is elusive—but about failures that lead to accidents by the Part 830 definition. This means that someone got killed or seriously hurt, or that the aircraft suffered “substantial damage.” We’re also not talking about the damage that results from an accident, but cases where the flight proceeds in good order until the moment that part of the aircraft breaks. If a hard landing collapses the gear, we’d count this as a landing accident; if the gear collapses during a taxi turn at normal speed, it’s a mechanical accident.

So: What’s your best guess? At first blush, it looks pretty clear, but this turns out to be one of those questions that require some unraveling. Over the past 20 years, mechanical failures caused 10 percent of the accidents on fixed-wing training flights compared to almost 16 percent of those on all other types of fixed-wing flights. But training flights also suffered a much higher share of landing accidents (44 percent of the total, compared to 25 percent of non-training accidents). As we noted in an earlier issue, student solos account for a disproportionate share of these, but dual instruction of primary students and advanced maneuvers like the 180-degree power-off spot landing also bulk up the count. Those excess landing smacks dilute the other percentages by inflating the total of which they form parts.

If we take landings out of the equation, the results are closer, but the difference persists. Mechanical problems caused 18 percent of non-landing training accidents and 21 percent of all accidents excluding landings on other flights. The difference seems slight, but it meets the usual standards of statistical significance. In other words, it’s unlikely that we’d see that much of a difference simply due to chance.

The types of mechanical problems that led to accidents differed as well. Powerplant failures accounted for just over 40 percent in both cases, but landing gear and brake problems caused substantially more grief in the training fleet, getting the blame for 29 percent of mechanical accidents compared to just 21 percent of those on other types of flights. No doubt this is another aspect of the hard life that’s also reflected in the excess number of landing accidents. It was offset by a lower incidence of accidents arising from fuel-system and electrical problems (14 percent versus 19 percent and 4 percent compared to 7 percent, respectively). Of course, the relatively simple fuel systems of most primary trainers and the preponderance of daytime training probably figure into this. Airframe and flight control failures are blessedly rare, thank goodness. They led to about 9 percent of the accidents on both types of flights, for a total of about 20 per year nationwide.

Of course, the fact that mechanical problems cause a smaller share of accidents during flight training (even after excluding landing crack-ups) doesn’t automatically mean that they’re less common. A smaller percentage of a larger total can equal a larger result. But a quick back-of-the-envelope calculation shows that the overall accident rate per hours flown is actually about 15 percent lower on instructional flights than for the rest of fixed-wing GA. Smaller multiplied by smaller gets smaller still, so at last we have our answer: Mechanical failures really do cause fewer accidents on training flights—a little over one-quarter fewer in the same amount of flight time. We hope this will help your instructors—and even more, your students—quit worrying and attend to the business at hand.

ASI Staff

David Jack Kenny

David Jack Kenny is a freelance aviation writer.

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