NTSB confirms plug was Rob Holland's undoing

Holland approached Langley Air Force Base in Hampton, Virginia, intending to land just after 11:30 a.m. on a Thursday leading up to a weekend airshow. His customized MXS-RH was one of a kind, with modifications including installation of counterweight plugs that Holland had requested from MX Aircraft Co. to fine-tune the balance of the elevator. Holland approached the runway at 130 knots, leveled off about 50 feet above the runway, and proceeded down the runway, porpoising twice, then pitching up violently, climbing several hundred feet, and rolling as the aircraft completed a half-loop into the ground.

Investigators found the left elevator counterweight plug 10 feet behind the wreckage. Witness marks on the threaded plug and on the nearby aircraft structure confirmed it had come loose during the flight and jammed the elevator at a critical moment. The NTSB investigation docket includes a Mandatory Safety Notice issued after the accident by MX Aircraft to owners of MXS and MX2 aircraft fitted with adjustable elevator balance tubes. The notice includes detailed instructions on how to replace any counterweights installed with a mixture of lead shot and resin while rebalancing the elevator.

Holland dominated the 4-Minute Freestyle event in international aerobatic competition for more than a decade, winning six times, along with 13 consecutive U.S. national championships. He was not the first pilot flying at the top levels of aviation competition to be killed by a custom modification intended to squeeze more performance out of an airplane. In 2011, Jimmy Leeward and 10 spectators were killed during the National Championship Air Races in Reno, Nevada, when Leeward lost control of the race-modified North American P–51 Galloping Ghost following the fracture of an elevator trim tab screw that led to a cascade of control failures.

In the case of the Galloping Ghost crash, investigators determined that several modifications intended to increase speed had not been subject to rigorous engineering analysis or tests that might have exposed a fatal flaw: The elevator trim tabs had a tendency to flutter at racing speed. In Holland's case, the NTSB final report notes that Holland's counterweight installation varied from the manufacturer's specifications.

"The manufacturer also stated the plug design incorporated an o-ring that would serve as a secondary locking mechanism. No o-ring was found on the recovered plug at the accident site, nor was one found on the still-installed right elevator’s counterweight plug," the report states. "Additionally, the plugs found installed on the accident airplane differed dimensionally from those specified in a design document provided by the airframe manufacturer. Based on the available information, it is likely that the left elevator counterweight plug loosened during the flight until it made contact with the washer and screw in the horizontal stabilizer, sufficient to jam the elevator. This ultimately resulted in the pilot being unable [to] control the airplane during the landing, and the subsequent impact with terrain."

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