Robert Sumwalt of the National Transportation Safety Board said there is no indication the plane's engines suffered a major failure or fire before it crashed into a hill about a mile before the Birmingham-Shuttlesworth International Airport landing strip Wednesday.
"Engines showed no sign of an uncontained failure or pre-impact fire. #UPS 1354," the NTSB Thursday posted on Twitter.
Investigators were able to retrieve both the flight-data and cockpit-voice recorders from the smoldering crash scene Thursday, The Wall Street Journal reported.
Sumwalt said he is "cautiously optimistic that we will be able to collect good data."
If the so-called black boxes don't indicate a mechanical problem with the jet, investigators will focus on how the crew handled the landing approach, the newspaper said.
Pilots familiar with the landing approach at the airport said it can be challenging because a hill must be cleared just prior to touchdown.
Both pilots on the plane died in the crash. UPS identified the captain of the aircraft as Cerea Beal, 58, of Matthews, N.C., and the first officer as Shanda Carney Fanning, 37, of Lynchburg, Tenn.
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