DUBAI, United Arab Emirates — Pilots on board a UPS cargo plane faced radio problems and smoke in the cockpit as they struggled to maintain altitude before crashing into the desert outside Dubai last week, investigators said Sunday.
What exactly caused Friday's crash remains under investigation. The UAE's General Civil Aviation Authority said in a preliminary report the Boeing 747-400's two-man crew was trying to return to Dubai's main airport — the Mideast's busiest — when the plane went down. Both crew members were killed.
Just over 20 minutes into the flight, air traffic controllers in Dubai received word from officials in the nearby Gulf nation of Bahrain that the plane was on its way back after reporting smoke in the cockpit. The jet was "unable to maintain altitude," the report said.
Crew members were unable to speak directly with air traffic controllers in Dubai as they attempted to land, however, because the pilot had already switched his radio to a different frequency and for some reason couldn't switch it back, Saif al-Suwaidi, the GCAA's director-general, told The Associated Press.
"What we know is the pilot couldn't change the frequency ... so the only solution was to relay the messages from Bahrain to Dubai," al-Suwaidi said.
Air traffic controllers informed the crew that all runways had been cleared for landing, but the plane came in "too high and too fast" and couldn't maintain the correct angle for approach, al-Suwaidi said. It passed over the airport before making a right turn toward the desert, then rapidly lost altitude and disappeared from the radar.
The plane — which has a wingspan of 212 feet (64.6 meters) and length of 232 feet (70.7 meters) — went down at 7:42 p.m., about 50 minutes after takeoff, in an unpopulated area between two major highways.
Flight 6 was en route to the UPS hub in Cologne, Germany.
Al-Suwaidi said it was unclear why the plane turned back toward Dubai rather than heading toward an airport in Bahrain, which was responsible for the plane's flight path when crew reported smoke in the cockpit.
"It is the pilot's decision. Once he declares an emergency, it is his responsibility to declare the most suitable airport," he said.
Emirati investigators sifted through the wreckage looking for clues Sunday. Members of the media were kept away from the debris field, located on a military camp.
The plane's cockpit voice recorder was recovered about six hours after the crash, the aviation authority said. Investigators are still searching for the plane's other "black box" — the digital flight data recorder — which could provide further details about what went wrong.
Al-Suwaidi ruled out terrorism or other foul play as possible causes.
A U.S. National Transportation Safety Board team is scheduled to arrive Sunday evening to help with the probe.
UPS, the Atlanta-based company formally known as United Parcel Service Inc., has identified the crew members killed as Captain Doug Lampe of Louisville, Kentucky, 48, and First Officer Matthew Bell, 38, of Sanford, Florida. Lampe has been with UPS since 1995. Bell has been with the company since 2006. Both flew out of UPS's Anchorage, Alaska, pilot base.
The shipping company, the world's largest, said the aircraft was three years old, was up to date on all maintenance and underwent an inspection in June.
Friday's accident was the area's second deadly cargo plane crash in less than a year. In October 2009, a Sudanese Boeing 707 cargo plane crashed in the desert after taking off from Sharjah airport just north of Dubai, killing six crew members. Emirati regulators have banned the plane's Sudanese owner, Azza Transport, from operating in the country.