Things With Wings

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  • Supersized Prang
    Posted by John Croft 1:14 AM on Feb 27, 2014

    The holes in the Swiss cheese accident model lined up perfectly for the crew of a large Russian freighter flying to Canada in August 2012.

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    According to a final report by the Canadian Transportation Safety Board, a tail wind and a braking system installation error by the Tashkent Aircraft Production Company were among the causes and contributing factors that led to an overrun of a Volga-Dnepr Ilyushin IL-76TD on Runway 11 at the St. John’s International Airport in Newfoundland, Canada in August 2012. Inbound from Prestwick, Scotland, the IL-76TD with 10 crew members on board landed long on the wet 8,502-ft. runway after an instrument landing system approach. The aircraft came to rest in the grass, with the nose wheel stopping 640 ft. beyond the end of the pavement, damaging five runway threshold lights in the process, but the crew had wisely steered the airplane to the right before exiting the runway to avoid multiple rows of approach lights.

    While the aircraft crossed the threshold at the correct altitude and speed and within what the pilots thought was the IL-76 ’s 10 kt. allowable tail wind for landing, information from the flight data recorder showed that the four-engine behemoth was actually experiencing a 13 kt. tailwind. Pilots have access to the computed winds in the cockpit but were required by Volga-Dnepr to use wind values provided by the airport terminal information service, which showed a tail wind component of 3 kt. After passing over the threshold, the crew erred by increasing the pitch angle and not immediately reducing thrust, extending the touchdown point to 4,220 ft. down the runway, investigators say. Once on the runway, braking of 16 main gear tires was not optimal due to tire conditions and an installation error for the antiskid system during production of the transport, which had logged 175 flight hours and 45 landings since delivery. The TSB says a visual examination of the gear after the accident showed that all 16 main gear tires “were worn to, or below, the tire tread wear indicators,” and that eight of the tires exhibited indications of hydroplaning.

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    On the antiskid system, investigators determined that the pressure supply lines had been installed according to assembly instructions at the Tashkent Aircraft Production Company, but were giving incorrect indications. When the antiskid system signaled release of braking pressure to an outboard wheel pair to prevent skidding, it instead released pressure to an inboard pair (and vice versa). “Consequently, during antiskid operations, overall braking capability would be reduced, as the pressure would be released to wheels with effective braking,” says the TSB. “Volga-Dnepr is working with [Tashkent] to resolve the discrepancy between what is shown on the brake line assembly chart and what is identified in the system design.”

    The cargo airline also changed its operating procedures to require crews to monitor wind speed in the cockpit during landings and to perform a go-around if the tail wind exceeds 10 kt. The runway itself also contributed to the excursion, as the friction levels were not optimal. According to the TSB , two months after the excursion the St. John’s International Airport Authority performed “runway texture improvement work” which resulted in a “large increase” in friction levels, reducing the potential for hydroplaning.

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