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Check and double checkCheck and double check

A few things are too important to ever take for granted

A well-worn—and well-justified—rule of thumb is to do an exceptionally detailed and rigorous preflight inspection of any aircraft that’s just had maintenance performed. Airframe and powerplant mechanics are as human as the rest of us, and mistakes are rare but hardly unknown.

Some, of course, are in places the pilot can’t inspect, like the clogged carburetor fuel screen that led to the ditching of a Cessna 206 in the middle of Lake Michigan, but over the years we’ve also seen aircraft brought down by discrepancies as obvious as reversed aileron cables, untightened nuts on a helicopter’s pitch-change control links, and even fuel selectors left in the “OFF” position.  Every one of those should have been detected before the aircraft left the ground. It’s especially difficult but especially important to switch to the perspective of the skeptical customer when the pilot is the one who did the work.

About 6:30 p.m. Sept. 27, 2016, a 1981-model Cessna 172P took off from the Davis Airport near Laytonsville, Maryland, to return to its base in Gaithersburg five miles away. Both airports lie within the Washington, D.C., Special Flight Rules Area (SFRA), so even that three-minute flight required the pilot to file an SFRA flight plan, obtain a discrete transponder code, and make radio contact with Potomac Approach. Moments after lifting off, the pilot radioed, “We’ve lost our engine, we’re going in.”  The transmission was scratchy and the controller replied, “You’ve lost a what, sir?” The Cessna pilot never replied, though two others did.

Several witnesses saw the airplane make a 180-degree turn from its initial southeasterly heading and begin “flying erratically.” It stabilized briefly, then “fell out of the sky sideways.” One witness reported being able to see “the complete top side of the plane” as it fell. A post-crash fire consumed most of the fuselage, including the cockpit. The NTSB concluded that the 1,200-hour commercial pilot stalled the Skyhawk trying to glide back to the field after the engine failed.

The cause of that failure was not hard to determine. Investigators found evidence of heat distress “consistent with a lack of lubrication” throughout the engine, including a seized oil pump, highly discolored crankshaft and connecting rod bearings, and two damaged pistons. No residual oil was found inside the rocker covers, cylinders, crankcase, or oil pump.

The pilot was also an A&P mechanic. He had flown the Cessna, which belonged to a flying club, to Davis to perform a 100-hour inspection. A surveillance camera on the Davis maintenance ramp actually captured footage of him pulling in, working on the airplane, and leaving again. Over the course of about four hours he drained the oil, removed the cowlings, cleaned the spark plugs and air filter, and inspected other components and accessories. He then replaced the cowlings and started the engine without ever refilling the crankcase. Another witness on the maintenance ramp said his run-up and takeoff sounded “normal.”

Many, if not most, pilots only run through the full preflight checklist before the first flight of the day. A few items, however, merit repetition any time the engine is shut down and restarted. The magneto test before takeoff is one, and the accident pilot did it. Checking the oil level is another. Under other circumstances, it wouldn’t be hard to imagine skipping this after a flight of only five minutes—a good argument for doing it unconditionally before every engine start. And a third is to verify healthy readings on the engine instruments, especially the oil temperature and pressure gauges, before advancing the throttle. Checking for “gauges in the green” might have come too late to save the engine, but almost certainly would have prevented the accident.

Almost everyone who has worked on mechanical devices has made a mistake at some point. That’s why the pilot must learn to distrust the mechanic … even when they’re one and the same.

ASI Staff

David Jack Kenny

David Jack Kenny is a freelance aviation writer.
Topics: Accident, Emergency, Loss of Control

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