Jeff Bezos went on 60 Minutes in 2013 and pledged to fill the skies with a fleet of delivery drones that could zip parcels to customers’ homes in 30 minutes. Asked when this future would arrive, the Amazon.com Inc. founder said he expected drone deliveries to commence in the next five years or thereabouts.

Almost a decade later, despite spending more than $2 billion and assembling a team of more than 1,000 people around the world, Amazon is a long way from launching a drone delivery service.

A Bloomberg investigation based on internal documents, government reports and interviews with 13 current and former employees reveals a program beset by technical challenges, high turnover and safety concerns. A serious crash in June prompted federal regulators to question the drone’s airworthiness because multiple safety features failed and the machine careened out of control, causing a brush fire. While experimental aircraft are expected to crash during test flights, current and former employees say pressure to get the program back on track has prompted some managers to take unnecessary risks that have put personnel in harm’s way.