NTSB official Todd Inman said "numerous" sources could have produced the sound, but it is too early in the investigation to offer further speculation.

Airport CCTV security footage showed the left engine “detaching from the wing during the takeoff roll,” according to Inman. The engine seen in photos from near the crash site is believed to be from the left side of the plane, he added.

NTSB member Todd Inman said the UPS plane was going 183 knots at an altitude of 475 feet before crashing south of Louisville's airport.

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.

A National Transportation Safety Board member said they are compiling a group of experts to review the recording.

Flight data showed the UPS plane that crashed taking off from Louisville's airport Tuesday was going 210 miles per hour at 100 feet of altitude at the last reading retrieved

The flight data (FDR) and cockpit voice (CVR) recorders have been flown to the NTSB lab in Washington D.C., where the information they contain will be analyzed. The FDR has 63 hours of information covering the last 24 flights made by the aircraft. The CVR contains two hours of audio, including the accident flight.

National Transportation Safety Board Member Todd Inman said video shows an engine detached from a UPS cargo plane shortly before it crashed at Muhammad Ali International Airport in Louisville, killing at least 12 people.