Amazon, the multi-trillion dollar e-commerce monolith, seemingly cheaped out on keeping a key feature installed on its delivery six-propeller drones. And predictably, this backfired almost immediately. On a rainy December day at the company's testing range in Oregon, not one but two Prime Air drones suddenly stopped spinning their propellers mid-flight and plummeted some 200 feet to the ground. The crashes, which destroyed both aircraft, happened within minutes of each other.  And now, Bloomberg reports, we know why. According to National Transportation Safety Board documents, bad readings from the drones' onboard lidar sensors led the drone to believe it had […]