Two Flight Disappearances Have Similarities and Differences

Indonesia AirAsia Flight 8501, an Airbus A320 airliner carrying 162 people, disappeared from radar screens early Sunday, about 40 minutes after leaving the Indonesian city of Surabaya en route to Singapore. A full day of searching the relatively shallow waters off the coast of Borneo has so far yielded no sign of the aircraft, raising a familiar mix of uncertainty and grief just nine months after Malaysia Airlines Flight 370 disappeared shortly after takeoff from Kuala Lumpur. Though Flight 8501 disappeared in a similar part of the world, it involves a different airline and a different type of aircraft.

Here are some basic details about what is known about the two disappearances.

- Unlike Malaysia Airlines, a financially struggling, state-controlled carrier, AirAsia, with headquarters near Kuala Lumpur, Malaysia, is a rapidly growing, low-cost airline with several affiliates - including Indonesia AirAsia - operating across Southeast Asia. Its fleet of 80 planes is relatively young, with an average age of less than five years.
- The aircraft that disappeared Sunday was a single-aisle Airbus A320-200 that was built in 2008. AirAsia is one of the world's largest operators of Airbus A320 series jets. Malaysia Airlines Flight 370 was a Boeing 777-200, a wide-body jet that was built in 2002.

- Until Sunday, AirAsia had had an unblemished safety record. Tony Fernandes, the current chief executive and a billionaire, bought AirAsia in 2001 from DRB-Hicom, a government-linked conglomerate. It was a small, heavily indebted airline then, which was originally established in 1994.

Weather

- In the case of Flight 370, the skies were clear and there were no unusual weather conditions or turbulence reported. In the AirAsia case, cumulonimbus cloud formations were reported in the area, and weather agencies reported a number of lightning strikes along the flight's planned route.

- In both cases, there was no emergency distress call issued by the crew. But in the case of Flight 8501, the pilots did inform air traffic controllers in Jakarta, Indonesia, that they were planning to increase their altitude to 38,000 feet from 32,000 feet to avoid what may have been a thunderstorm. This is why many experts have focused on weather conditions as a possible contributing factor in the disappearance of the AirAsia flight. In the case of Flight 370, the last communication from the flight with the ground was a "good night" message to Malaysian air traffic controllers just before the plane was supposed to cross into Vietnamese airspace. Instead, Flight 370 veered sharply off its intended course to Beijing, for reasons that remain unexplained.

Communications

- Aside from the voice communications between the pilots and air traffic controllers, there would have been periodic automatic transmissions of certain flight performance and maintenance data sent from the computers on board the plane. The Indonesian authorities have not yet released any details about what information those transmissions contained, but in past accidents, these have provided important clues about what happened.

- In the case of Flight 370, the amount of such data was limited because one of those automated systems, the Aircraft Communications Addressing and Reporting System, or ACARS, was among the systems that are believed to have been manually disabled in the cockpit. But in the case of another flight, Air France Flight 447, which disappeared off the coast of Brazil in 2009, investigators had access to a cascade of error messages that were sent over the ACARS system that indicated, among other issues, a problem with the plane's airspeed sensors that ultimately disabled the plane's autopilot system.

- There has so far been no indication in the case of the AirAsia flight that the crew took any action to disable any onboard systems. In the case of Flight 370, investigators believe that the plane's transponders and other communications systems were deactivated manually by someone in the cockpit, possibly one of the pilots.

Pilots

- One of the more confounding details about Flight 370 was the fact that its captain was extremely experienced, with more than 18,000 hours of flying experience. That flight's co-pilot was less experienced on the Boeing 777, and had around 2,700 hours under his belt. The combined flight experience of the two pilots of the AirAsia flight was much less: The captain had a total of 6,100 flying hours, while the first officer had a total of 2,275 flying hours.

Status of Flight 370

- Flight 370 left Kuala Lumpur on March 8 on an overnight flight to Beijing with 239 people on board, but its communications inexplicably turned off course and headed south. A series of fleeting satellite communications signals from the aircraft that were captured by a ground station in Perth, Australia, indicated that the flight had most likely come down somewhere over the Indian Ocean, off the west coast of Australia, when it ran out of fuel.

- A three-month search for debris on the sea surface, as well as efforts to locate the audio beacons attached to the plane's so-called black boxes, covered 1.7 million square miles but has failed to turn up any trace of Flight 370. In October, a new hunt began along a vast arc of rugged seabed that is thought to have been the plane's final flight path based on calculations made from the satellite ping series.

- The Australian authorities charged with the latest search phase have said they are cautiously optimistic that they will eventually find the jet with the help of an array of high-tech equipment that includes side-scan sonar, synthetic aperture sonar, multibeam echo sounders and sophisticated video cameras.