Nine people remain missing after a UPS plane departing Louisville Muhammad Ali International Airport in Kentucky on Tuesday crashed, killing at least 12 people.

Dozens of federal aviation investigators are on the ground in Louisville searching the crash site's debris field, which covers nearly a half-mile area.

As a bell sounded in the cockpit, three UPS pilots tried to control a cargo flight that crashed this week in Louisville, Kentucky, killing at least 13 people, the National Transportation Safety Board said on Friday.

The UPS cargo plane crew tried to control the aircraft for about 25 seconds before it crashed into a ball of flames shortly after taking off on Tuesday.

The cockpit voice recorder captured a persistent bell that began about 37 seconds after the crew called for takeoff thrust, and the bell continued until the recording ended, an NTSB official said.

UPS and FedEx have grounded their MD-11 cargo aircraft after a deadly UPS plane crash in Louisville, Kentucky, left at least 14 people dead. The decision followed Boeing’s recommendation to suspend flights for safety checks as investigators probe the cause of the accident.

LOUISVILLE, Ky. (WXIX) - The cockpit voice recorder and flight data recorder were both recovered from the wreckage of the deadly UPS plane crash in Louisville. The National Transportation Safety Board posted a photo of the recorders from the MD-11 cargo plane on Thursday morning.

A UPS cargo plane crashed at a Louisville, Kentucky, airport where the company operates its largest package delivery hub. UPS calls the giant center Worldport.