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In 2011, Flight School Business derived a back-of-the-envelope estimate that in a given number of flight hours, mechanical failures cause about 25 percent fewer accidents during training than during noninstructional flights. Not mentioned in that article was the fact that on training flights, they’re also more survivable. In the most recent decade for which we have solid data, just 11 of 175 mechanical accidents on fixed-wing instructional flights (6 percent) caused fatalities, compared to 186 of the 1,847 on flights for all other purposes (10 percent).

In addition to the preponderance of smaller, slower airplanes in primary training, flight instruction benefited—if that’s the word—from a difference in the types of systems and components that actually failed. On noninstructional flights, powerplant problems represented the single largest category, at nearly 41 percent. On training flights, landing gear and brake failures were No. 1. These caused 37 percent of all mechanical accidents, but no deaths. By contrast, 11 percent of powerplant failures were lethal.

Of course, as we’ve noted before, percentages are slippery. Anyone who has been a student pilot can see that this might represent an excess number of gear problems on instructional flights rather than a reduced risk of powerplant failures; it could also be a mix of both. In fact, after standardizing by FAA estimates of hours flown, it turns out that the rate of accidents caused by gear and brake failures is actually about one-third lower on instructional flights—while the rate of accidents caused by powerplant malfunctions is nearly two-thirds less. Apparently the benefits of warming the oil regularly manage to outweigh the harm inflicted by all those thumped landings.

Less reassuring is the fact that many of those failures resulted from maintenance that was done improperly or deferred too long, or from discrepancies that went unnoticed on recurrent inspections (sometimes for years). In 2005, for example, a Cessna 152 conducting spin training failed to recover. Investigators found the rudder still jammed beyond its normal deflection limit because the rubber bumpers had been installed inverted, allowing the right bumper to travel beyond its stop and become locked there. Paint on the bumpers matched the paint job put on the airplane in 1997, meaning that the discrepancy had gone undetected through at least seven annuals.

Two years earlier, a student pilot made a successful forced landing after losing aileron control in a Piper Archer. The screw securing the control wheel to the control column had backed out, and subsequent inspection found that the same screw was loose in 10 of the school’s other 35 Piper trainers.

Other discrepancies were less subtle. In 2010 a private pilot and his instructor barely escaped an in-flight fire in a Piper Warrior after making an emergency landing. The cause of the fire wasn’t hard to find: The “B” nut connecting the output line to the fuel pump hadn’t been tightened. The airplane’s annual inspection had been signed off just two days earlier.

Another CFI made a successful forced landing in a swamp in 2012 after a Cirrus SR22 threw its No. 2 connecting rod. Not only had the engine had been run nearly 1,000 hours beyond its recommended time between overhaul, but the owner chose not to follow the service bulletin mandating an engine teardown after finding pieces of a piston pin bushing in the oil sump. His school routinely flew the airplane with five quarts of oil, one less than the minimum prescribed by the POH. That maintenance philosophy was apparently shared by the owner of a Cessna 172, who added hydraulic fluid to an obviously leaky brake master cylinder but took no further action. That airplane subsequently carried a CFI and a new student off the end of a taxiway, down an embankment, and into the trees after the brakes failed.

Even when no accident results, obviously neglected maintenance hardly inspires confidence in either students or their families. One AOPA staff member recalls training at a notoriously marginal school. On her first solo cross-country, the heading indicator fell out of the panel into her lap when she began climbing to clear higher terrain. (She made the flight anyway, using the compass to navigate.) On her second, she found the airplane slowing for reasons that remained mysterious until she noticed that the flaps were extending. The flap switch was so worn that the weight of its handle was pulling it down; she made the rest of the flight holding the lever in the full-retracted position. When the same operator tried to dispatch an airplane with obvious engine oil leaks for a multi-state family trip, she decided she’d had enough and took her business elsewhere.

We can hope the recent recession weeded out most of those who consider skipping maintenance an acceptable way to cut costs. We can also suggest that an evident commitment to their upkeep is the most effective way to make well-used trainers feel familiar and secure.

ASI Staff

David Jack Kenny

Manager, Safety Analysis
David Jack Kenny analyzes GA accident data to target ASI’s safety education programs while also supporting AOPA’s ongoing initiatives and assisting other departments in responding to breaking developments. David maintains ASI’s accident database and regularly writes articles for ePilot, Flight School Business, Flight Training, CFI-to-CFI, and other publications.

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