AirAsia Flight QZ8501 took off early Sunday morning from the Indonesian city of Surabaya, en route to Singapore with 162 passengers and crew on board.
But the Airbus A320-200 disappeared from radar 42 minutes after takeoff, amid reports of stormy weather and without any distress call being issued.
Here's what we know so far about the missing plane.
The flight was mostly over water
AirAsia Flight QZ8501 took off at 5:35 a.m. local time on Sunday (5:35 p.m. ET Saturday) from Juanda International Airport in Surabaya, a city in eastern Java, for a two-hour flight northwest to Changi Airport in Singapore.
The flight path would have taken the plane over the relatively shallow Java Sea between the islands of Borneo and Sumatra.
The weather was nasty
The airspace was thick with storm clouds. One of the jet's pilots asked to raise the plane's altitude to avoid the bad conditions.
The plane didn't get quick clearance to climb
The last communication from the cockpit was the pilot's request to increase altitude from 9,754 metres to 11,582 metres.
Air traffic control was not able to immediately grant the request because another plane was in the airspace, said Bambang Tjahjono, director of the state-owned company in charge of air traffic control.
By the time clearance could be given, Flight 8501 had disappeared, Tjahjono said.
A multi-faceted search is underway
The search has been focused on a 240-square-kilometre area between the island of Belitung, off Sumatra, and Borneo island, said Indonesian Transport Minister Ignasius Jonan.
Twelve navy ships, five planes, three helicopters and a number of warships were taking part in the search, along with ships and planes from Singapore and Malaysia, said First Adm. SigitSetiayana, the Naval Aviation Center commander at the Surabaya air force base. The Australian air force also sent a search plane.
Many fishermen from Belitung island have also joined the search, and vessels in that area have been alerted to be on the lookout for anything that could be linked to the plane.
Searchers have seen things — but we don't know what they mean
Crew on an Indonesian helicopter have reported two oil slicks on the Java Sea east of Belitung island, close to where the plane lost contact.
"Suspicious" objects were seen by crew on an Australian Orion aircraft near Nangka island, about 160 kilometres off central Kalimantan and about 1,200 kilometres from the place where contact was lost with the flight.
Neither instance has been confirmed to be related to the missing jetliner.
The pilot had a lot of experience
The plane's captain, who goes by the single name of Iryanto, has logged more than 20,000 flying hours. More than 6,000 of them are with AirAsia, according to reports.
Family, neighbours and friends say Iryanto is an experienced air force pilot who flew F-16 fighter jets before he turned to commercial flying, the Daily Telegraph reported.
Indonesian media reported the captain's daughter Angela posted a message to her father on a social networking site.
"Papa come back. I still need you. Return my papa to me. Papa come back, we have to meet," the message said, according to the Malaysian Insider website.
The BBC reported that Iryanto's father, Sawarto, saw his son last week at the funeral of another son. Now, Suwarto says, whatever happened, "it was in the hands of fate," the BBC reported.
The Airbus A320 is a workhorse
Airbus describes the A320 jetliner group as "the world's best-selling single-aisle aircraft family." The planes are widely considered to be workhorse aircraft for short-haul flights.
AirAsia has been the largest commercial airline customer of the A320, ordering 184 planes and taking delivery of 157, CNN reported.
Airbus says the aircraft used for Flight QZ8501 on Dec. 28 was delivered to AirAsia in October 2008 and has 23,000 flight hours logged during 13,600 flights.
AirAsia said the aircraft had its last scheduled maintenance on Nov. 16.
The A320 has also made headlines in North America — that was the plane pilot Chesley Sullenberger guided to a safe landing on the Hudson River in New York City in 2009.
It's been a tough year for airlines in Southeast Asia
The AirAsia disappearance comes nine months after Malaysia Airlines Flight MH370 disappeared en route from Kuala Lumpur to Beijing. The plane with 239 passengers and crew on board has not been found.
Four months later, another Malaysia Airlines jet, flight MH17, was shot down over Ukraine. All 298 people on board were killed.
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