Rescuers believe they have found the plane on the ocean floor off Borneo, after sonar detected a large, dark object beneath waters near where debris and bodies were found on the surface.
Ships and planes had been scouring the Java Sea for Flight QZ8501 since Sunday, when it lost contact during bad weather about 40 minutes into its flight from the Indonesian city of Surabaya to Singapore.
Seven bodies have been recovered from the sea, some fully clothed, which could indicate the Airbus A320-200 was intact when it hit the water. That would support a theory that it suffered an aerodynamic stall.
The fact that one person put on a life jacket suggests those on board had time before the aircraft hit the water, or before it sank.
And yet the pilots did not issue a distress signal. The plane disappeared after it asked for permission to fly higher to avoid bad weather.
"This morning, we recovered a total of four bodies and one of them was wearing a life jacket," Tatang Zaenudin, an official with the search and rescue agency, told Reuters.
He declined to speculate on what the find might mean.
A pilot who works for a Gulf carrier said the life jacket indicated the cause of the crash was not "catastrophic failure". Instead, the plane could have stalled and then come down, possibly because its instruments iced up and gave the pilots inaccurate readings.
"There was time. It means the thing didn't just fall out of the sky," said the pilot, who declined to be identified.
He said it could take a minute for a plane to come down from 30,000 feet and the pilots could have experienced "tunnel vision ... too overloaded" to send a distress call.
"The first train of thought when you get into a situation like that is to fly the aircraft."
Most of those on board were Indonesians. No survivors have been found.
Hernanto, head of the search and rescue agency in Surabaya, said rescuers believed they had found the plane on the sea bed with a sonar scan in water 30-50 meters (100-165 feet) deep. The black box flight data and cockpit voice recorder has yet to be found.
Authorities in Surabaya were making preparations to receive and identify bodies, including arranging 130 ambulances to take victims to a police hospital and collecting DNA from relatives.
"We are praying it is the plane so the evacuation can be done quickly," Hernanto said.
Strong wind and waves hampered the search and with visibility at less than a kilometer (half a mile), the air operation was called off in the afternoon.
"We are all standing by," Dwi Putranto, heading the air force search effort in Pangalan Bun on Borneo, told Reuters.
"If we want to evacuate bodies from the water, it's too difficult. The waves are huge and it's raining."
Indonesian President Joko Widodo said his priority was retrieving the bodies.
Relatives, many of whom collapsed in grief when they saw the first grim television pictures confirming their fears on Tuesday, held prayers at a crisis center at Surabaya airport.
AirAsia Chief Executive Tony Fernandes has described the crash as his "worst nightmare".
EXPERIENCED PILOT
The plane was traveling at 32,000 feet (9,753 meters) and had asked to fly at 38,000 feet. When air traffic controllers granted permission for a rise to 34,000 feet a few minutes later, they received no response.
Online discussion among pilots has centered on unconfirmed secondary radar data from Malaysia that suggested the aircraft was climbing at a speed of 353 knots, about 100 knots too slow, and that it might have stalled.
Investigators are focusing initially on whether the crew took too long to request permission to climb, or could have ascended on their own initiative earlier, said a source close to the inquiry, adding that poor weather could have played a part as well.
The Indonesian captain, a former air force fighter pilot, had 6,100 flying hours under his belt and the plane last underwent maintenance in mid-November, said the airline, which is 49 percent owned by Malaysia-based budget carrier AirAsia.
Three airline disasters involving Malaysian-affiliated carriers in less than a year have dented confidence in the country's aviation industry and spooked travelers.
Malaysia Airlines Flight MH370 went missing in March on a trip from Kuala Lumpur to Beijing with 239 passengers and crew and has not been found. On July 17, the same airline's Flight MH17 was shot down over Ukraine, killing all 298 people on board.
On board Flight QZ8501 were 155 Indonesians, three South Koreans, and one person each from Singapore, Malaysia and Britain. The co-pilot was French.
The AirAsia group, including affiliates in Thailand, the Philippines and India, had not suffered a crash since its Malaysian budget operations began in 2002.
