BEIJING - As the search for a missing AirAsia passenger plane stretched into its third day, authorities widened their survey area and asked for outside help, even as hopes dimmed among families of the 162 people aboard the jet.
Indonesia's state-owned navigation provider AirNav gave local media a detailed account Monday of Flight 8501's last contact with air traffic controllers on Sunday.
Wisnu Darjono, AirNav's safety and standard director, said the pilot asked Soekarno-Hatta airport's air traffic control at 6:12 a.m. for permission to turn left to avoid bad weather. Permission was granted, and the plane turned seven miles to its left flank, the Jakarta Post reported.
The pilot then requested to climb from 32,000 to 38,000 feet but did not explain why.
Jakarta's air traffic control conferred with Singapore-based counterparts and agreed to allow increasing the altitude to 34,000 feet because a second AirAsia flight was flying at 38,000 feet.
But by the time air traffic controllers relayed the permission to climb at 6:14 a.m., there was no reply, Darjono said.
Indonesian authorities said Monday that they believe the plane is already at the bottom of the sea, based on the plane's last coordinates and the estimated crash position, near Belitung island in the Java Sea.
That complicates the search, prompting them to ask the United States, Britain, and France for more advanced equipment. The Pentagon said details of that assistance are still being worked out, but would likely include "air, surface, and sub-surface detection capabilities."
An Indonesian helicopter crew spotted two oily patches Monday afternoon. But search officials said it is too soon to tell whether they were related to the Singapore-bound aircraft.
In a statement issued late Monday, search officials said they have deployed 12 helicopters, 11 planes, and 32 ships, including assets from Malaysia, Singapore, and Australia - with more than 1,100 personnel involved. Even fishing boats have been tapped in the widespread search for wreckage, authorities said.
The sudden disappearance and frustrating maritime search is eerily similar to the Malaysia Airlines jetliner, Flight MH370, that disappeared over the Indian Ocean in March. The whereabouts of the plane, with 239 people aboard, are still a mystery.
Investigators are trying to locate debris from the crash and then work backward following currents to find the wreckage on the seabed. To do so, they will need ships equipped with advanced sonar and search vehicles that can look for signs of the wreckage underwater, experts said. Once the wreckage is found, the cockpit voice and flight data recorders would offer the most substantial clues as to what went wrong.
After two days of challenging search conditions, authorities can expect "perfect weather" Tuesday and Wednesday, Adi Eka Sakya, the head of Indonesia's Meteorology, Climatology and Geophysics Agency, said at a Jakarta news conference. But torrential rains could return Friday.
An Australian search plane on Monday afternoon reported seeing objects hundreds of miles away, but Indonesian officials later said they were unrelated to the plane.
Even as the reason for the crash remained unclear, shares of AirAsia dropped sharply in trading on Monday.
Indonesian officials' speculation that the plane is already underwater would explain the lack of a signal from its emergency locator transmitter, said Australia-based aviation security expert Desmond Ross. "All these aircraft have this beacon that triggers on impact and sends a signal to satellites," Ross said. "If it's gone to the bottom of the sea, we probably wouldn't hear that signal."
Experts said the disappearance has prompted several tantalizing questions.
Bad weather appeared to play a role, but it is unclear why the pilot was not able to avoid it earlier, said Ross, noting that modern commercial jets are equipped with radar that can spot bad weather more than 100 miles ahead.
The speed of the airplane is likely to be at the forefront of any investigation, said John Cox, a former accident investigator. Radar suggests that the plane was flying at a low speed, Cox said. Overly slow speed at a high altitude could cause an airplane to stall with insufficient lift to sustain flight, he said.
Many experts have compared the AirAsia flight to the crash of an Air France flight in 2009 in which airspeed measurements failed, leading pilots to put the plane into a stall. While wreckage of the Air France flight was spotted within days, it took two years for the black-box recorder to be found and retrieved from the Atlantic Ocean.