The 322-page investigation into the crash, which killed both pilots, backed up preliminary probes pointing to the lithium batteries as the possible cause of the blaze and drew further attention to the potential risks of the batteries in aviation.
Lithium batteries have been the subject of fire-related probes on the Boeing 787 "Dreamliner." The entire 787 fleet was grounded for about three months earlier this year after a fire in a battery on a Japan Airlines 787 parked at Boston's Logan International Airport, and a smoking battery that led to an emergency landing by an All Nippon Airways 787 in Japan.
The report noted that investigators could not cannot pinpoint the factors that started the fire, describing it as a "chain reaction which spread to the available combustible material" and apparently was not spotted by smoke detectors in its early moments.
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The report included more than 35 recommendations, including better early-warning systems in cargo holds to detect fires, and adding equipment that could aid pilot visibility in smoky conditions.
It added that shippers of some of the lithium battery cargo loaded onto the plane in Hong Kong "did not properly declare these shipments" and did not provide battery test reports recommended under UN aviation guidelines.
Before publication of the report, UPS had begun implementing new systems to improve pilot vision and protocols to quickly use full-face oxygen masks when needed, said a statement from the Independent Pilots Association in Louisville, Kentucky.