Streamers approached the wreckage of an Amazon Air cargo plane hours after a crash that killed five people; authorities are still investigating the cause of the runway overrun

An investigation was launched by the National Transportation Safety Board (NTSB), but tests kept coming up inconclusive until one investigator took a novel approach. That final test proved that the dual servo valve inside the power control unit (PCU) was jamming from exposure to extreme cold followed by extreme heat.

The National Transportation Safety Board (NTSB) Chair Jennifer Homendy held a press briefing on Monday after a Boeing Co. BA cargo aircraft, part of e-commerce giant Amazon.com Inc.‘s AMZN “Prime Air,