NEW YORK (AP) — Rescue crews are searching Indonesian waters for AirAsia Indonesia Flight 8501, which disappeared Sunday with 162 passengers and crew onboard. The plane was flying from Surabaya, Indonesia's second-largest city, and was about halfway to its destination, Singapore, when it vanished from radar. 
 
 ___ 
 
 Q: WHAT COULD HAVE HAPPENED? 
 
 A: It is way too early to know for sure, but here are some options. The plane was in the safest part of flight: Just 10 percent of fatal crashes from 2004 through 2013 occurred while a plane was at cruise elevation, according to a safety study published by Boeing in August. 
 
 Passing through bad weather such as severe thunderstorms could have been a factor. Airbus jets have sophisticated computers that automatically adjust to wind shears or other weather disruptions. But weather — combined with pilot errors — has played a role in past air disasters that occurred at cruise elevation, including the 2009 Air France Flight 447 crash over the Atlantic Ocean. 
 
 Another possibility is some type of catastrophic metal fatigue caused by the cycle of pressurization and depressurization associated with each takeoff and landing cycle. This A320 had had 13,600 takeoffs and landings. Many occurred in humid climate, which speeds corrosion. Still, metal fatigue is unlikely because this plane is only 6 years old. 
 
 Finally, there's the possibility of terrorism or a mass murder by the pilot. There's no evidence of either action, but neither can yet be ruled out. 
 
 ___ 
 
 Q: WHAT DID THE PILOTS SAY TO AIR TRAFFIC CONTROLLERS? 
 
 A: The last communication between the pilot and air traffic control was at 6:12 a.m. Sunday (6:12 p.m. EST Saturday) when the pilot "asked to avoid clouds by turning left and going higher to 38,000 feet (11,582 meters)." The last radar contact occurred three minutes later. There was no distress call. But pilots are trained to focus first on the emergency at hand and then communicate only when free. 
 
 ___ 
 
 Q: ISN'T THIS THE THIRD MALAYSIAN JET TO CRASH THIS YEAR? 
 
 A: Malaysia Airlines Flight 370 disappeared with 239 people aboard soon after takeoff from Kuala Lumpur for Beijing on March 8. Its whereabouts and what happened remain one of the biggest mysteries in commercial aviation. Another Malaysia Airlines flight, also a Boeing 777, was shot down over rebel-controlled eastern Ukraine while en route from Amsterdam to Kuala Lumpur on July 17. All 298 people aboard were killed. AirAsia is also based in Malaysia. Flight 8501 was operated by AirAsia Indonesia, a subsidiary that's 49 percent owned by the Malaysian parent company. So technically, it's an Indonesian airline. But the AirAsia brand is closely tied to the people of Malaysia. 
 
 ___ 
 
 Q: IS THERE A CONNECTION AMONG ALL THESE CRASHES? 
 
 A: No. It's just a very unfortunate year for Southeast Asia. But that doesn't stop conspiracy theories from sprouting. Ideas about what happened to Flight 370 — both logical and bizarre — keep appearing. The unsolved nature of that disappearance could generate more attention for Flight 8501 and create a new batch of hypotheses. 
 
 ___ 
 
 Q: HOW FAR COULD THE JET HAVE FLOWN? 
 
 A: Looking at the flight's paperwork, the plane had more than 18,000 pounds of jet fuel at takeoff, enough to fly about 3½ hours, according to Phil Derner Jr., the founder of aviation enthusiast website NYCAviation.com and a flight dispatcher for a U.S. airline. He notes that that's less fuel than most flights tend to carry from New York to Florida. 
 
 ___ 
 
 Q: WHAT'S NEXT? 
 
 A: Indonesia, Singapore and Malaysia are conducting a search-and-rescue operation near Belitung island in the Java Sea, the plane's last known whereabouts. Assuming that the jet didn't veer far off course, the searchers should find wreckage, which can provide clues about what happened. Investigators will also try to recover the flight data and cockpit voice recorders, which often have the most detailed information about the plane's final moments. Those so-called black boxes have homing beacons that help searchers find them. 
 
 ___ 
 
 Q: IS THE AIRBUS A320 A SAFE JET? 
 
 A: The plane is a workhorse of modern aviation. Similar to the Boeing 737, the single-aisle, twin-engine jet is used to connect cities that are between one and five hours apart. Worldwide, 3,606 A320s are in operation, according to Airbus, which also makes nearly identical versions of the plane: The smaller A318 and A319 and the stretched A321. An additional 2,486 of those jets are flying. The A320 family has a good safety record, with just 0.14 fatal accidents per million takeoffs, according to the Boeing safety study. 
 
 ___ 
 
 Q: WHAT ABOUT AIRASIA? 
 
 A: Low-cost AirAsia has a strong presence in most of Southeast Asia, and it recently expanded into India. Though most of its flights are just a few hours long, it has tried to expand into long-distance flying through its sister airline AirAsia X. None of its subsidiaries has lost a plane before, and it has a generally good safety record. But it does fly in a part of the world where air travel has expanded faster than the number of qualified pilots, mechanics and air traffic controllers. 
 
 ___ 
 
 Q: WHAT ABOUT FLYING IN INDONESIA? 
 
 A: The country has had a bumpy safety record. In 2007, the crash rate and safety standards were so bad that the European Union barred all of Indonesia's airlines from flying into any of its member countries. Than ban was lifted in 2009. But Indonesia's main airline — fast-growing Lion Air — is still banned by the EU. 
 
 ___ 
 
 Q: WHAT'S IT LIKE TO FLY THROUGH A THUNDERSTORM AT 34,000 FEET? 
 
 A: Planes flying through thunderstorms experience severe turbulence, with the aircraft moving up, down, sideways and rolling. Anything not secured can float around in the cabin, bouncing off things and people. Overhead bins can open up, spilling contents. Airsickness is common. 
 
 ___ 
 
 Q: WHAT DO PILOTS DO TO AVOID THUNDERSTORMS? 
 
 A: If at all possible, airline pilots fly around thunderstorms, even if it means going far out of their way. Airliners like the A320 typically are equipped with radar that provides highly accurate weather information. Pilots can see a thunderstorm forming from over 100 miles away, giving them time to plot a way around the storm cluster or to look for gaps to fly through. It's usually not a problem for commercial planes to go 100 or more miles out of the way. 
 
 ___ 
 
 Q: HOW HIGH CAN AN A320 SAFELY FLY? AND WHAT IF IT EXCEEDS THAT LIMIT? 
 
 A: The A320 is certified to fly up to 39,000 feet, its maximum altitude before its rate of climb begins to erode. The plane has an absolute flight limit of 42,000 feet. But it can begin to experience problems as low as 37,000 feet, depending on temperature and weight, including fuel, cargo and passengers. The plane's computers should reveal the maximum altitude at which the plane can fly at its current weight and temperature. Planes that exceed their maximum altitude may lose lift, causing an aerodynamic stall. Or they can experience a pressurization blowout, damaging the plane. 
 
 ___ 
 
 Q: HOW DOES A PLANE JUST FALL OFF RADAR? 
 
 A: It's still unclear what traffic controllers saw on their screens when the plane disappeared from radar. Authorities haven't said whether they lost only the secondary radar target, which is created by the plane's transponder, or whether the primary radar target, created by energy reflected from the plane, was lost as well. If a plane came apart in the air or suffered a loss of electrical power, the secondary target would be lost, but the primary target is often still visible on radar. But if the plane were descending at rate of over 6,000 feet a minute — typical of a plane about to crash — the primary target might be lost as well. 
 
 ___ 
 
 Q: HOW VITAL IS AIR TRAVEL TO THE REGION? 
 
 A: For many people, it's the only option. Indonesia is a sprawling archipelago of 250 million people. To get from one island to another, the easiest way is to fly. As the region's economy has grown, so have the number of people flying. The International Air Transport Association recently named Indonesia as one of the world's five fastest-growing air travel markets, predicting an additional 183 million passengers would take to the sky within two decades. 
 
 Routes to, from and within the Asia-Pacific region are predicted by the industry trade group to see an extra 1.8 billion annual passengers by 2034, for an overall market size of 2.9 billion. Within two decades, the region is expected to account for 42 percent of global passenger traffic. 
 
 The increase in regional airline traffic reflects rapid economic growth. The International Monetary Fund expects the Southeast Asian economies of Indonesia, Malaysia, Philippines, Thailand and Vietnam to grow faster this year and next than anywhere except China, India and sub-Saharan Africa. 
 
 ___ 
 
 Scott Mayerowitz can be reached at http://twitter.com/GlobeTrotScott 
 
 ___ 
 
 Lowy contributed from Austin, Texas. Paul Wiseman in Washington also contributed to this report. ||||| (CNN) -- An oil slick, the sound of a distant "ping," objects in the water, and now this: smoke spotted rising from an island in the Java Sea. 
 
 As ships, planes and helicopters scour the waters off Indonesia's coast for missing AirAsia Flight QZ8501, there have been several reports of possible signs of the missing plane. 
 
 So far, officials say, none of them have panned out. 
 
 On Tuesday, search teams will be checking the area where Indonesian navy helicopter crews saw the smoke, the head of search and rescue in the province of Bangka-Belitung told CNN Indonesia. But authorities don't know whether there's any connection to the missing jet. 
 
 Local media in Indonesia reported the smoke was seen on Long Island, one of thousands that make up the archipelago that forms Indonesia. 
 
 Searchers have been scanning the water's surface for signs of the plane, which went missing with 162 people aboard on Sunday as it flew between the islands of Belitung and Borneo, a heavily traveled shipping channel with shallow waters. 
 
 "Our early conjecture is that the plane is in the bottom of the sea," said Bambang Sulistyo, the head of Indonesia's search-and-rescue agency. That belief is based on the plane's flight track and last known coordinates, he said. 
 
 Several possible signs of the missing plane, including an oil slick within the search zone and the sound of a faint "ping," have been discounted, according to Indonesian authorities, who are heading the search. 
 
 Indonesia Vice President Jusuf Kalla said there were "some reports from Australia" about possible objects found, but it was unclear whether they were from the plane. 
 
 Because there is a great deal of traffic along the water in the search area, authorities have cautioned that objects found might have nothing to do with the missing aircraft. 
 
 Rescuers say weather was probably a factor in the plane's disappearance, and it has made finding traces of the plane more difficult. 
 
 Large waves and clouds hampered the search for the plane on Sunday and Monday. 
 
 "It is not easy, of course ... the operation in the sea, especially in the bad weather like this," Kalla said. 
 
 But Kalla said his country will not give up or set a time limit for the operation. 
 
 The search area is expanding, with six zones added to the operation on Tuesday, Sulistyo told reporters. 
 
 Now, he said, teams in the air, on sea and on land are searching 13 zones over an area that stretches about 156,000 square kilometers (60,200 square miles). 
 
 What role did weather play? 
 
 Report: Higher altitude request denied 
 
 AirAsia says air traffic controllers lost contact with the aircraft at 7:24 a.m. Sunday, Singapore time (6:24 a.m. in Indonesia). 
 
 The plane, flying from the Indonesian city of Surabaya to Singapore, went missing as it flew over the Java Sea between the islands of Belitung and Borneo -- a heavily traveled shipping channel with shallow waters -- Indonesian authorities said. 
 
 Before the plane, an Airbus A320-200, lost contact with air traffic controllers, one of the pilots asked to change course and fly at a higher altitude because of bad weather, officials said. Heavy thunderstorms were reported in the area at the time. 
 
 Air traffic control approved the pilot's request to turn left but denied permission for the plane to climb to 38,000 feet from 32,000 feet, Djoko Murjatmodjo, an aviation official at the Indonesian Transport Ministry, told the national newspaper Kompas. 
 
 The increased altitude request was denied because there was another plane flying at that height, he said. 
 
 Djoko suggested that Flight 8501 ascended despite air traffic control denying it permission. 
 
 AirAsia CEO Tony Fernandes said storm clouds caused the pilot to ask for a flight plan change. But he added, "We don't want to speculate whether weather was a factor. We really don't know." 
 
 Once the aircraft is found, there will be a proper investigation, Fernandes said. 
 
 AirAsia CEO takes to Twitter 
 
 Relatives to be flown over search area 
 
 Amid the anxious wait, family members of the passengers have attended closed-door briefings with airport and airline officials at the airport in Surabaya. 
 
 Oei Endang Sulsilowati and her daughter were looking for information about her brother, his wife and their two children. 
 
 "We don't know what to do," Sulsilowati said. "We are just waiting for news." 
 
 A specially chartered plane will fly relatives of passengers over the search area Wednesday, AirAsia Indonesia CEO Sunu Widjatmoko told reporters in Surabaya on Tuesday. 
 
 The chartered Airbus A320 that will take families from Surabaya over the zone has room for as many as 180 people, he said. 
 
 Some police said authorities were seeking additional materials to help identify passengers, such as photos with close-ups of teeth, DNA, or fingerprints. But police officials later told CNN they were not immediately seeking these materials. 
 
 East Java Police have set up a disaster victims identification area at the Surabaya airport. 
 
 Of the people on board the passenger jet, 155 are Indonesian, three are South Korean, one is British, one is French, one is Malaysian and one is Singaporean, the airline said. 
 
 Eighteen children, including one infant, are among the passengers, the carrier said. Seven of the people on board are crew members. 
 
 Families of AirAsia flight passengers given support through the 'nightmare' 
 
 International search team 
 
 Since the flight disappeared in Indonesian airspace, Indonesia is heading up search efforts. 
 
 More than 1,100 search and rescue personnel from Australia, Singapore, Malaysia, South Korea, Japan and New Zealand are joining the search alongside Indonesia's teams, CNN Indonesia reported. 
 
 The missing plane is made by Airbus, a French company. And France has dispatched two investigators to Indonesia. They are due to arrive in Jakarta on Monday, France's Foreign Ministry said. 
 
 Malaysia's transportation minister said his country has deployed three vessels and three aircraft to assist in the search. And the Royal Australian Air Force said Monday that it was deploying a patrol plane to help. 
 
 The USS Sampson is on its way to the Java Sea to assist in the search for the missing AirAsia plane, a senior U.S. military official told CNN Chief National Security Correspondent Jim Sciutto. The Sampson, a guided-missile destroyer based in San Diego, deployed in October to take part in "maritime security exercises and training" in the Pacific. 
 
 China will dispatch aircraft and ships to participate in search and rescue efforts, the Chinese Ministry of National Defense said Tuesday. 
 
 The MH370 mystery 
 
 AirAsia, a successful budget airline group headquartered in Malaysia, had a clean safety record until the disappearance of Flight 8501. The missing plane is operated by the company's Indonesian affiliate. 
 
 The loss of contact with the plane comes nearly 10 months after the disappearance of Malaysia Airlines Flight 370, which dropped off radar over Southeast Asia on March 8 with 239 people on board. 
 
 AirAsia and MH370 cases are very different 
 
 Searchers have yet to find any remains of Flight 370, which officials believe went down in the southern Indian Ocean after mysteriously flying thousands of kilometers away from its planned route from Kuala Lumpur to Beijing. 
 
 But some aviation experts don't think the search for Flight 8501 will be as challenging as the hunt for MH370. 
 
 "We are not talking about the deep Indian Ocean here," CNN aviation correspondent Richard Quest said. "We are talking about congested airspace around Southeast Asia. There will be much better radar coverage. There's certainly better air traffic control coverage." 
 
 CNN's Susanna Capelouto, Andrew Stevens, Paula Hancocks and Lucia Isman contributed to this report. Azieza Uhnavy also contributed to this report.
– The disappearance of another jet in Southeast Asia while the fate of Malaysia Airlines Flight 370 remains a mystery comes as a shock to the aviation world, but experts stress that the two cases are very different. The New York Times runs through some of the differences with AirAsia Flight 8501: Unlike with Flight 370, there has been no sign that anybody on Flight 8501 intentionally disabled any onboard systems, meaning that investigators should have the normal automatic transmissions from the flight to help the search. Flight 370 disappeared on a clear night, while Flight 8501 was believed to have encountered stormy weather, with weather agencies having reported lightning strikes along its route. The AirAsia pilot's last communication with air traffic control was a request "to avoid clouds by turning left and going higher to 38,000 feet." Flight 370's pilot was very experienced, with more than 18,000 hours of flying time, while the combined experience of Flight 8501's pilot and co-pilot is believed to be less than half that. Neither Flight 370 nor Flight 8501 issued an emergency distress call, but, as the AP notes, "pilots are trained to focus first on the emergency at hand and then communicate only when free," and there's no sign that the AirAsia flight diverted sharply from its intended course the way the Malaysia Airlines flight did. Another major difference is the search area for Flight 8501, which is much smaller and shallower than the vast area that has been searched for Flight 370. "We are not talking about the deep Indian Ocean here," says CNN aviation correspondent Richard Quest. "We are talking about congested airspace around Southeast Asia. There will be much better radar coverage. There's certainly better air traffic control coverage."