SURABAYA, Indonesia -- - An Indonesian helicopter saw two oily spots in the search area for the missing AirAsia jetliner Monday, and an Australian search plane spotted objects hundreds of miles away, but it was too early to know whether either was connected to the aircraft and its 162 passengers and crew, officials said.
Flight 8501 vanished Sunday on a flight from Indonesia to Singapore.
Earlier, a rescue official said the plane is likely "at the bottom of the sea."
The search expanded Monday, with planes and ships from several countries taking part.
Flight 8501 vanished in airspace thick with storm clouds on its way from Surabaya, Indonesia, to Singapore, and a rescue official said Monday that given the route of the plane he believed the most likely scenario was that it crashed.
"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," National Search and Rescue chief Henry Bambang Soelistyo told a news conference.
The last communication from the cockpit to air traffic control was a request by one of the pilots to increase altitude from 32,000 feet to 38,000 feet because of the rough weather. Air traffic control was not able to immediately grant the request because another plane was in airspace at 34,000 feet, 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.
The twin-engine, single-aisle plane, which never sent a distress signal, was last seen on radar four minutes after the last communication from the cockpit.
Sources told CBS News correspondent Jeff Pegues that the search likely won't drag out and the chances of finding black boxes are much better than other missing jet searches because the ocean is shallower and the area much more heavily trafficked.
First Admiral Sigit Setiayana, the Naval Aviation Center commander at the Surabaya air force base, said that 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.
Setiayana said visibility was good. "God willing, we can find it soon," he told The Associated Press.
The U.S. Navy said that it had not yet been asked to assist in the search.
"As we have in the past, the U.S. Navy assets in 7th Fleet stand ready to assist in any way that's helpful," the Navy said in a statement.
The plane's disappearance and suspected crash caps an astonishingly tragic year for air travel in Southeast Asia. The Malaysia-based carrier's loss comes on top of the still-unexplained disappearance of Malaysia Airlines Flight 370 in March and the downing of Malaysia Airlines Flight 17 in July over Ukraine.
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.
The Airbus A320 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.
CBS News aviation and safety expert Capt. Chesley "Sully" Sullenberger said in an interview on CBSN that "it's appropriate that these pilots requested deviation" and that not much should be read into the lack of a distress call.
"It's likely the pilots were busy with higher priority items," Sullenberger said, adding that he himself had 5,000 hours in that type of plane.
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 told 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."
Earlier, Fernandes tweeted:
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 13,400 meters (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, who like many Indonesians uses only one name.
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 more than 20,000 flying hours, of which 6,100 were with AirAisa 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 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 Nov. 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.
Sullenberger said that the A320 is a widely used plane and when "used properly," the aircraft "can do its job efficiently."
Flight 8501 disappeared while at its cruising altitude, which is usually the safest part of a trip. Just 10 percent of fatal crashes from 2004 to 2013 occurred while a plane was in that stage of flight, the safety report said.