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Inadequate restraints have been blamed for the loss of National Air Cargo flight at Bagram in 2013. Although disputed by the carrier, which wanted to see an investigation into the possibility that an explosive device was involved, the NTSB board voted unanimously that the probable cause of the crash was that at least one of the five armoured military vehicles shifted as the aircraft took off. A strap had already broken on the previous flight. The NTSB found the airline had inadequate procedures in place for restraining cargo and training crew, while regulators had failed to provide proper oversight. It was the first time National had tried to carry five of the vehicles at once. The NTSB contended that if Boeing’s weight and balance manuals had been consulted, the loadmaster would have known that the load “could not be properly secured in the airplane in accordance with … safety requirements.”