Australia has joined the search and rescue mission for missing AirAsia flight QZ8501, with hopes of finding any of the 162 on board alive fading rapidly amid predictions the plane was likely "on the bottom of the sea".
Officials at Indonesia's search and rescue agency said on Monday the plane was presumed to have crashed off the Indonesian coast.
Late on Monday, Indonesian Vice-President Jusuf Kalla confirmed an Australian Orion aircraft had spotted debris in the ocean at the edge of the search zone, but it could not yet be verified whether it was related to the missing plane.
The Indonesia AirAsia plane, an Airbus A320-200, disappeared after its pilot failed to get permission to alter course to avoid bad weather during a flight from the Indonesian city of Surabaya to Singapore on Sunday.
Flight QZ8501 did not issue a distress signal and disappeared over the Java Sea five minutes after requesting a change of course.
"Based on our co-ordinates, we predict that the plane is [in] the sea, for now it could be [on] the bottom of the sea," said Bambang Soelistyo, the head of Indonesia's search and rescue agency.
Australia offered an RAAF AP-3C Orion aircraft from Darwin to assist with the search, and it joined Indonesian, Malaysian and Singaporean aircraft scanning the region from first light on Monday.
Prime Minister Tony Abbott said the event was tragic but not a mystery like the disappearance of Malaysian Airlines flight MH370 in March, nor was it an atrocity like the shooting down of MH17 in July.
"It's an aircraft that was flying a regular route on a regular schedule, it struck what appears to have been horrific weather and it's downed," Mr Abbott told Macquarie Radio.
Nevertheless, aviation experts would be "putting their heads together to come up with the most effective way of ensuring that we don't just lose planes", the prime minister said.
Foreign Affairs Minister Julie Bishop said Australia's focus was on helping find the plane.
"At this stage we are just hoping and praying that some passengers and crew can be rescued," Ms Bishop said.
But she warned that "as time goes on" fears about the fate of the 162 passengers and crew would likely be confirmed.
No Australians were on board but the government is cross-checking the flight manifest to see if any dual Australian citizens were on board.
Defence Force Chief Mark Binskin said the P3 Orion has "a well-proven capability" in search and rescues and carries maritime search radar, infra-red technology and electro-optical sensors.
Ms Bishop said Singapore had also provided support for the search effort given it was the country where the plane was originally due to land after its departure from Indonesia.
Speaking to ABC television, Ms Bishop revealed that during her conversation with Ms Marsudi she reflected on how aircraft disasters had brought Australia and Indonesia closer together in 2014.
"I was talking to Foreign Minister Marsudi about Malaysia Airlines MH17 because she was Indonesia's ambassador to the Netherlands during the MH17 tragedy," she said.
"Indonesia lost 12 citizens on that flight, so we were discussing how sad it was that so often when we speak it's in relation to an emergency or a tragedy involving an airline."
Bad weather
As international aircraft scoured a large area of the Karimata Strait, west of Belitung, air transportation director at Indonesia's transport ministry, Joko Muryo Atmodjo, said there had been bad weather in the area at the time and the aircraft had been flying at 32,000 feet before asking to fly at 38,000 feet to avoid clouds.
Permission had not yet been given due to traffic in the area and five minutes later, at 6.17am on Sunday, the plane lost contact with air traffic control, Mr Atmodjo added.
Data from Flightradar24.com, which tracks airline flights in real time, showed several nearby aircraft were at altitudes ranging from 34,000 to 36,000 feet at the time, levels that are not unusual for cruising aircraft.
An A320 pilot from a south-east Asian airline who has flown the Surabaya-Singapore route many times said it was not unusual to request a slight deviation or climb due to poor weather.
"It is not uncommon at this time of the year, and I have done this myself. It would not have been an unusual request and [air traffic control] will usually grant permission," said the pilot, who declined to be identified because he was not authorised to talk to the media.
Disastrous year
Onboard flight QZ8501 were 155 Indonesians, three South Koreans, one person each from Singapore, Malaysia and Britain, while the co-pilot was French.
With Indonesia AirAsia 49 per cent owned by Malaysia-based budget carrier AirAsia, the incident caps a disastrous year for Malaysia-affiliated airlines.
Malaysian Airlines flight MH370 went missing on March 8 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.
The AirAsia group, including affiliates in Thailand, the Philippines and India, has not suffered a crash since its Malaysian budget operations began in 2002. The group's shares in Kuala Lumpur fell as much as 12.9 per cent on Monday.
"We are co-operating with the relevant authorities to the fullest extent to determine the cause of this incident," said Indonesia AirAsia Chief Executive Sunu Widyatmoko.
The Indonesian pilot was experienced and the plane last underwent maintenance in mid-November, the airline said. The aircraft had accumulated about 23,000 flight hours in some 13,600 flights, according to Airbus.
Malaysia AirAsia chief Tony Fernandes flew to Surabaya and, along with Indonesian officials, updated distraught relatives of passengers at a makeshift crisis centre at the airport in Indonesia's second-largest city.
"This is my worst nightmare," Mr Fernandes said on Twitter. "But there's no stopping," he said of the search.
with Latika Bourke
