SURABAYA: Search planes and ships from several countries on Monday, were scouring Indonesian waters over which an AirAsia jet carrying 162 people disappeared, and more than a day into the region's latest aviation mystery, officials doubted there could be anything but a tragic ending.

AirAsia Flight 8501 vanished Sunday in airspace thick with storm clouds on its way from Surabaya, Indonesia, to Singapore. The search expanded Monday, but has yet to find any trace of the Airbus A320.

“Based on the coordinates that we know, the evaluation would be that any estimated crash position is in the sea, and that the hypothesis is the plane is at the bottom of the sea,” Indonesia search and rescue chief Henry Bambang Soelistyo said at a news conference.

First Adm. Sigit Setiayana, the Naval Aviation Center commander at the Surabaya air force base, said 12 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.

The Australian Air Force also sent a search plane. Searchers had to cope with heavy rain Sunday, but Setiayana said Monday that visibility was good.

“God willing, we can find it soon,” he told The Associated Press.

At the Surabaya airport, passengers' relatives pored over the plane's manifest, crying and embracing. Nias Adityas, a housewife from Surabaya, was overcome with grief when she found the name of her husband, Nanang Priowidodo, on the list.

The 43-year-old tour agent had been taking a family of four on a trip to Singapore, Malaysia and Indonesia's Lombok island.

"He just told me, 'Praise God, this new year brings a lot of good fortune,'" Adityas recalled, while weeping.

Nearly all the passengers and crew are Indonesians, who are frequent visitors to Singapore, particularly on holidays. Flight 8501 took off Sunday morning from Indonesia's second-largest city and was about halfway to Singapore when it vanished from radar. The jet had been airborne for about 42 minutes.

There was no distress signal from the twin-engine, single-aisle plane, said Djoko Murjatmodjo, Indonesia's acting director general of transportation. The last communication between the cockpit and air traffic control was at 6:13 a.m. (23:13 GMT Saturday), when one of the pilots asked to increase altitude from 32,000 feet to 38,000 feet, Murjatmodjo said.

The jet was last seen on radar at 6:16 a.m. and was gone a minute later, he told reporters. Indonesia, Singapore and Malaysia launched a search operation near Belitung island in the Java Sea, the area where the airliner lost contact with the ground. AirAsia group CEO Tony Fernandes flew to Surabaya and said at a news conference that the focus for now should be on the search and the families rather than the cause of the incident.

“We have no idea at the moment what went wrong,” said Fernandes, a Malaysian businessman who founded the low-cost carrier in 2001. "Let's not speculate at the moment."

Malaysia-based AirAsia has a good safety record and had never lost a plane. But Malaysia itself has already endured a catastrophic year, with 239 people still missing from Flight 370 and all 298 people aboard Flight 17 killed when it was shot down over rebel-held territory in Ukraine.

AirAsia said Flight 8501 was on its submitted flight plan but had requested a change due to weather. Sunardi, a forecaster at Indonesia's Meteorology and Geophysics Agency, said dense storm clouds were detected up to 44,000 feet in the area at the time.

“There could have been turbulence, lightning and vertical as well as horizontal strong winds within such clouds,” said Sunardi. Airline pilots routinely fly around thunderstorms, said John Cox, a former accident investigator. Using on-board radar, flight crews can typically see a storm forming from more than 100 miles away.

In such cases, pilots have plenty of time to find a way around the storm cluster or look for gaps to fly through, he said.

“It's not like you have to make an instantaneous decision,” Cox said. Storms can be hundreds of miles long, but "because a jet moves at 8 miles a minute, if you to go 100 miles out of your way, it's not a problem."

Authorities have not said whether they lost only the secondary radar target, which is created by the plane's transponder, or whether the primary radar target, which is created by energy reflected from the plane's body, was lost as well, Cox said.

The plane had an Indonesian captain, Iryanto, who uses one name, and a French co-pilot, five cabin crew members and 155 passengers, including 16 children and one infant, the airline said in a statement. Among the passengers were three South Koreans, a Malaysian, a British national and his 2-year-old Singaporean daughter. The rest were Indonesians.

AirAsia said the captain had more than 20,000 flying hours, of which 6,100 were with AirAsia on the Airbus 320. The first officer had 2,275 flying hours.

“Papa, come home, I still need you,” Angela Anggi Ranastianis, the captain's 22-year-old daughter pleaded on her Path page late Sunday, which was widely quoted by Indonesian media. "Bring back my papa. Papa, please come home."

At Iryanto's house in the East Java town of Sidoarjo, neighbors, relatives and friends gathered Monday to pray and recite the Holy Quran to support the distraught family. Their desperate cries were so loud, they could sometimes be heard outside where three LCD televisions had been set up to monitor search developments.

“He is a good man. That's why people here appointed him as our neighborhood chief for the last two years,” said Bagianto Djoyonegoro, a friend and neighbor.

Many recalled him as an experienced Air Force pilot who flew F-16 fighter jets before becoming a commercial airline pilot. The missing aircraft was delivered to AirAsia in October 2008, and the plane had accumulated about 23,000 flight hours during some 13,600 flights, Airbus said in a statement.

The aircraft had last undergone scheduled maintenance on November 16, according to AirAsia. The airline, which has dominated cheap travel in Southeast Asia for years, flies short routes of just a few hours, connecting the region's large cities.

Recently, it has tried to expand into long-distance flying through sister airline AirAsia X. The A320 family of jets, which includes the A319 and A321, has a good safety record, with just 0.14 fatal accidents per million takeoffs, according to a safety study published by Boeing in August.

Flight 8501 disappeared while at its cruising altitude, which is usually the safest part of a trip. Just 10 per cent of fatal crashes from 2004 to 2013 occurred while a plane was in that stage of flight, the safety report said.

Multinational search

Shortly before disappearing, the pilot asked to ascend by 6,000 feet to 38,000 feet to avoid heavy clouds, according to an Indonesian transport ministry official.

“The plane requested to air traffic control to fly to the left side, which was approved,” Djoko Murjatmodjo told a press conference.

"But their request to fly to 38,000 feet from 32,000 feet could not be approved at that time due to traffic, there was a flight above, and five minutes later the flight disappeared from radar."

“According to our climate radar, the weather was not good. There was enough cumulonimbus (cloud) there,” said Murjatmodjo.

He said Indonesia had deployed seven aircraft, four navy ships and six boats from the search and rescue agency.

The search focused on waters around the islands of Bangka and Belitung in the Java Sea, across from Kalimantan on Borneo island.

But Murjatmodjo said the transport ministry had also asked the army to carry out ground searches, including in mountainous areas.

“We have focused all our strength, from the search and rescue agency, the military, police and help from the community as well as the fishermen,” said rescue agency chief F.H.B. Soelistyo.

He said three ships and three planes from Malaysia would join the search Monday. A Singaporean C130 plane joined Sunday's operation, and two Singaporean planes would be deployed Monday with Australia also offering help.

France's air accident investigation authority, the BEA, said two safety investigators, accompanied by two Airbus technical advisors, would leave for Jakarta on Sunday evening.

'Massive shock'

The aircraft was operated by AirAsia Indonesia, a unit of Malaysian-based AirAsia which dominates Southeast Asia's booming low-cost airline market.

AirAsia's flamboyant boss Tony Fernandes, a former record industry executive who acquired the then-failing airline in 2001, arrived in Surabaya, where most of the passengers are from.

“Obviously this is a massive shock to us and we are devastated by what has happened. It's unbelievable,” he told a press conference.

"We don't want to speculate. We don't know what's happened yet so we'll wait for the accident investigation... Our concern right now is for the relatives and the next of kin."

Indonesia's President Joko Widodo said his nation was “praying for the safety” of those onboard.

His country, a vast archipelago with poor land transport infrastructure, has seen explosive growth in low-cost air travel over recent years.

But the air industry has been blighted by poor safety standards in an area that also experiences extreme weather.

AirAsia, which has never suffered a fatal accident, said the missing jet last underwent maintenance on November 16. Climbing to dodge large rain clouds is a standard procedure for aircraft in these conditions.

“What happens after that is a question mark,” according to Indonesian-based aviation analyst Dudi Sudibyo.

Missing flight is 3rd Malaysia-linked incident

The plane's disappearance comes at the end of a disastrous year for Malaysian aviation. The disappearance of the Malaysia Airlines Boeing 777 on March 8 triggered one of modern aviation's most perplexing mysteries.

Read also: Missing Malaysia Airlines plane triggers Southeast Asia search

Flight 370, carrying 239 people from Kuala Lumpur to Beijing, vanished without a trace, sending searchers across vast areas of the Indian Ocean. Investigators believe the aircraft ran out of fuel and crashed, based largely on an analysis of transmissions between the plane and a satellite.

In another incident, all 298 passengers and crew aboard Malaysia Airlines Flight 17 were killed when the Boeing 777 was shot down over rebel-held eastern Ukraine on July 17.

The plane was flying from Amsterdam to Kuala Lumpur when, according to Dutch air crash investigators, it was likely struck by multiple “high-energy objects” that some aviation experts say is consistent with a missile strike.