Initial details gleaned from the recorders - commonly known as "black boxes" - appear to confirm pilot reports of smoke in the cockpit less than half an hour after takeoff from the Middle East's busiest airport in Dubai.
The two pilots, hobbled by radio difficulties that kept them out of direct contact with Dubai's tower, attempted to turn back to the Gulf city state but were unable to land on their first attempt and crashed into a military base shortly afterward. Both men were killed.
The UAE's General Civil Aviation Authority is leading the investigation into the Sept. 3 crash with help from investigators at US National Transportation Safety Board.
GCAA Director-General Saif Al-Suwaidi told The Associated Press that the plane's flight recorders were sent to a laboratory in the US late last week for further analysis "under the custody of GCAA staff." Investigators said they found the plane's cockpit voice recorder about six hours after the crash. The other black box - the digital flight data recorder - was recovered in "reasonable" condition days later.
While investigators continue to analyze data on the recorders, an initial analysis shows "there was a fire warning followed by smoke in the cockpit as reported by the crew about 28 minutes from takeoff," the GCAA said in a statement distributed through Emirati state news agency WAM.
For reasons still unclear, the crew was unable to switch their radio frequency back to the Dubai channel and could not communicate directly with air traffic controllers there as they attempted to land, Al-Suwaidi told the AP two days after the accident. They instead had to relay information through air traffic controllers from the nearby Gulf nation of Bahrain.
Bahraini controllers gave the crew the option of landing in the Qatari capital Doha - located between Dubai and Bahrain's main airport - but that they decided to turn back to Dubai, where they "they experienced cockpit visibility and communication problems" before issuing a mayday call, the GCAA said Tuesday.
"The captain was in control up to the end of the recording," the aviation authority added.
UPS Flight 6 was bound for the shipping giant's hub in Cologne, Germany. Atlanta-based UPS is formally known as United Parcel Service Inc.
Data on the recorders will likely be compared with information already received from a sophisticated data transmission system installed on the plane. The system, known as an airplane health management system, is able to transmit performance information rapidly via satellite to UPS's airline operations headquarters in Louisville, Kentucky.
Accident investigators have told the AP that a fire appears to have begun in a cargo compartment just forward of the starboard wing. One theory being considered is that the plane may have been carrying lithium-ion batteries in the cargo hold. If a battery short-circuits, it can catch fire and ignite others.
Shortly after the crash, Al-Suwaidi said it appeared the plane was mainly carrying electronic goods, including toys and computer accessories. The manifest stated the 747-400 was carrying general cargo, he said.
