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Shifting prioritiesShifting priorities

By David Jack Kenny

Commercial operators aren’t allowed to be so casual, but a great many of us who only fly under Part 91 come to view weight-and-balance calculations as a trick to be demonstrated on checkrides and flight reviews. That’s not totally unreasonable given that the loading envelopes for most light aircraft are what mathematicians call convex spaces: If two points are inside the envelope, every point on the line between them will be too. That means that if you know you’re within CG limits flying solo and also with a 270-pound flight instructor (and the same fuel load), taking your 120-pound niece should be just fine. Many models require some creativity to push the CG outside limits while remaining below the certified maximum gross weight.

Of course, that’s not always the case, and another flight review parlor trick involves figuring out which passengers or cargo to shift where to place the center of gravity where it belongs. Implicit in the entire exercise is the assumption that, once moved, things will stay where you put them. Payload that shifts of its own accord has a way of confounding those calculations.

About 5:45 p.m. on July 16, 2014, at least seven witnesses saw a Piper PA-32R-301T overfly a private grass strip on North Captiva Island on the Florida Gulf Coast. Three of the seven knew the pilot and were aware that he’d been attempting to land after a short trip to Fort Myers Beach on the mainland. Even though its engine was reported to be “screaming,” the airplane did not appear to be climbing as it crossed the beach westbound out over the Gulf; the consensus estimate was that it was about seven feet above the sand. A slight left bank resulted in the left wingtip hitting the water, quickly followed by the entire airplane. Attempts to rescue the pilot were unsuccessful; the fuselage and right wing were eventually recovered from about 10 feet of water. The left wing separated during the accident sequence and was also recovered.

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Physical examination largely ruled out both mechanical failure in the 15-year-old airplane and medical emergency on the part of the 2,000-hour private pilot. However, one potential causal factor did emerge from the wreckage. The pilot had removed the two middle seats to use the center section of the fuselage as a cargo bay. In it he’d loaded 666 pounds of ceramic tile for a house remodeling project, the second such load he’d brought in that day.

Investigators noted two potential problems with that use of the aircraft. The weight in that central fuselage compartment exceeded the maximum authorized by 57 pounds—not a huge amount, but in no way smaller on a July evening in Florida.  They also estimated that the gross weight of the airplane was no more than 53 pounds below its authorized maximum, and it would have been that light only if the left tank had been run entirely out of fuel.

Probably more important, though, was the fact that the tiles hadn’t been tied down. The NTSB calculated a range of weight-and-balance estimates for various positions within the rear cabin, and concluded that the center of gravity might have been anywhere from 3.4 inches ahead of the aft limit to nearly four inches behind. More to the point, they realized that even if they’d been placed forward—resulting in a more nose-heavy attitude and possible difficulty flaring for landing—the tiles might easily have shifted backward during the transition to a go-around, rendering the airplane nearly or entirely uncontrollable.  Their factual report suggests that the crash into the water was a stall that the airplane no longer had elevator authority to avert after the load slid all the way back during the go-around.

This isn’t the only accident we’ve seen that arose from weight shifting unexpectedly in flight. If you’re going to bet your life on the accuracy of your flight planning, you might at least want to make sure everything stays where you put it in your plan.