CNN — BIRMINGHAM, Alabama (CNN) -- A preliminary investigation has found no evidence of an "uncontained engine failure" or a "pre-impact fire" in the engine of a UPS cargo plane that crashed in Birmingham, Alabama, killing the pilot and co-pilot, a National Transportation Safety Board official said Thursday.
There also was no indication of a problem with runway lights, Robert Sumwalt of the NTSB told reporters.
The news came as authorities announced the cockpit voice and flight data recorders were recovered from the wreckage near Birmingham-Shuttlesworth International Airport, and were being sent to NTSB headquarters in Washington.
"We are cautiously optimistic that we will be able to collect good, usable data," Sumwalt said.
The recorders were blackened and coated with soot from the fire that engulfed the plane on impact. But they are made to withstand crashes and heat, Sumwalt said.
Investigators had to use picks and shovels to retrieve the data recorders from the wreckage because flames in the plane's tail section kept officials from accessing them immediately.
The devices could help investigators determine why the plane -- which did not issue a distress call -- went down early Wednesday while on approach to the airport.
UPS identified the pilots as Capt. Cerea Beal Jr., 58, of Matthews, North Carolina, and First Officer Shanda Fanning, 37, of Lynchburg, Tennessee.
Beal had been with UPS since 1990 and previously had served six years in the U.S. Marine Corps as a heavy lift helicopter pilot, according to a statement released by UPS.
Fanning had worked for UPS since 2006, the statement said.
The Airbus A300-600F broke into pieces as it crashed around 4:45 a.m. in an open field near a street that runs parallel to the airport.
The cargo plane had 12 "service difficulty" reports on file at the Federal Aviation Administration, including at least two that the reports indicated led pilots to declare emergencies.
But an aviation expert told CNN he believes none of the previous problems would have played a role in the accident.
The reports document problems ranging from an inoperative light in an emergency exit light assembly to a problem with the plane's flaps.
"I don't see anything there that indicates in any way that its related to the events in Birmingham," said John Goglia, a former NTSB member and former certified aircraft mechanic.
The flap problem, reported in 2006 while the plane was flying in Germany, might raise concern had it not occurred so long ago, he said.
Witnesses said the plane, which took off from Louisville, Kentucky, flew low over a neighborhood, striking the tops of trees and knocking down power lines as it crashed.
The crash site is about a half mile north of a runway.
A photo showing the jet engine blades only partially damaged could indicate that the engines were not running or were at "very low idle" upon impact, instead of the faster "flight idle" typical upon landing, Goglia said.
"An engine that is producing power, those (blades) would have been gone," said Goglia. The lack of damage suggests that "they weren't spinning so fast and they stopped quickly."
If the data recorders contain information, investigators should be able to quickly discover the status of the engines before impact.
But if the data is not retrievable, investigators will focus on the condition of the blades, Goglia predicted.
Airbus said Wednesday the plane had approximately 11,000 flight hours in some 6,800 flights. It was powered by Pratt & Whitney engines.
The plane was one of two flights UPS sends to Birmingham each day, company spokesman Mike Mangeot told CNN affiliate WBRC.
The crew did not report any trouble, Birmingham Mayor William Bell said, citing conversations with control tower officials. Light showers and a visibility of 10 miles were reported in the area of the airport at the time of the crash, according to CNN meteorologist Dave Hennen.