The disappearance of Malaysia Airlines Flight 370 has left investigators, aviation experts and the authorities in several countries at a loss to explain what happened. And the few slender clues that have emerged only seem to lead to more questions. As the search broadens and the international inquiries continue, Matthew L. Wald, a correspondent for The New York Times, answers some basic questions:
Q. The Times has reported that Malaysian military radar systems saw the plane climb and dive. Does this indicate that a hijacker was at the controls?
A. Not necessarily. Aerodynamics experts say that if an airplane is set up to fly a straight path at a given altitude, it will eventually vary from that altitude, for two reasons. First, it will burn off fuel, and a lot of that fuel is stored in the tanks at the jet’s wingtips, which are behind the airplane’s center of gravity. As the back of the plane gets lighter, the tail will rise and the nose will fall. As the plane dives, it will pick up speed. But with more speed there will be more lift and the nose will rise. The aircraft will then climb until speed decreases and the nose will point down again, repeating the cycle in an oscillation. Second, if the plane flies close to the speed of sound, then the center of pressure and the center of lift will move toward the back of the aircraft, pushing the nose down. Other factors at play include the accuracy of the military radar in estimating altitude. The Malaysian military has not described its radar’s capabilities, so if the plane were recorded at 45,000 feet, what is the range of uncertainty in that measurement? Turns would be much harder to explain without human intervention, but a plane that encounters certain natural weather phenomena can turn.
Q. How easy is it to switch off the communications equipment on the plane?
A. You have to know what you are looking for, but it is not that difficult. Just about everything on the plane has a circuit breaker, which is accessible to the pilots. The equipment could be legitimately shut off for several reasons. One reason is that if the equipment stops working, the solution often involves powering down the equipment and then powering it up again, the way someone would do with a frozen computer. Also, if a component has a short circuit and overheats or catches fire, there has to be a way to turn it off. This is why transponders (most planes carry more than one) can easily be switched off from the cockpit.
Q. If the communications equipment has been switched off, is there anything else onboard that could still send a signal?
A. The plane is built to communicate with satellites and there is a second system, not easily controlled from the cockpit, to accomplish that. Even when it is not in use, the system goes through a “handshake” procedure with satellites, about once an hour. This procedure is akin to a cellphone that trades messages with the nearest cell tower, even though it never leaves the user’s pocket, so the cell system knows where to find it should a call come in. That handshake does not include data, experts say, but it does offer a way to establish the approximate location of the plane once an hour. American experts say they knew little about this system until this week, when it yielded a clue, albeit a weak one, to the Malaysian plane’s location.
Q. Will we ever know what happened?
A. Some investigators are warning that we may never know what happened. The cockpit voice recorder, which would be crucial in determining if the crash were the result of a hijacking or some other criminal act, captures just two hours of sound, continuously recording over earlier information. But this flight apparently lasted six hours and the period that matters most probably was not within the final two hours. Recovering the voice recorder also presumes that searchers locate the wreckage of the plane. The cockpit voice recorder and the flight data recorder (which has a 25-hour loop) have battery-powered “pingers” attached, which emit a sound that can travel several miles through the water. Their batteries only last an average of 30 days. Searchers in other crashes have found the boxes without the help of “pingers,” but it is much more difficult.
Q. How could a Boeing 777 simply vanish? Aren’t they always tracked by radar or satellites?
A. Radar coverage is not universal, especially over water. In areas without radar, pilots are generally required to radio in their positions at fixed intervals, mostly to assure that air traffic controllers can keep aircraft out of one another’s way. Between intervals, something could go wrong.
Planes like the 777 also have automatic systems that send out data on engine performance and other technical functions. Those signals go to a maintenance base, not to air traffic control. Air France used those signals to help determine what happened when its Flight 447 disappeared over the equatorial Atlantic, and the satellite system installed on the Malaysia Airlines jet has yielded clues about where to look for it, though not its precise location.
Q. Plane crashes most often happen on landing or takeoff, but this flight vanished almost an hour after takeoff, when it was cruising. What could cause a plane to crash at that point in a flight?
A. In three crashes at sea in the last few years, the aircraft’s speed-sensing systems have malfunctioned. In two of those cases, crews failed to diagnose and cope with the problem. (In the third, there was probably nothing they could have done.) A deliberate act by a pilot, terrorism or an attack in the cockpit could be other causes.
Q. Why would the authorities not have found debris from the plane after so many days of searching?
A. One reason is that much of the searching was done in what authorities now believe were the wrong places. In the first days, the focus was on the waters of the Gulf of Thailand and the South China Sea, close to where the plane was when ground controllers last heard from the pilots or saw signals from its transponders. Military radar data then emerged showing that the plane had turned far off course and flown westward toward the Strait of Malacca and the Andaman Sea, so some searchers were shifted there. Then satellite signals indicated that the plane had kept flying for hours more, hugely expanding the possible search area. By the time the primary focus narrowed again to the southern Indian Ocean, nearly two weeks had gone by, time in which the elements could have scattered or sunk some debris that might have been visible immediately after the crash.
Q. How far from its last known location could the aircraft have strayed?
A. While we know fairly precisely where the plane was when contact was lost, we have only inferences from radar and satellite data about how long it remained in the air afterward or which way it flew, so it is hard to say with certainty. The plane had enough fuel on board to complete its scheduled journey to Beijing, 2,500 miles from Kuala Lumpur, so it conceivably could have kept flying for seven hours or more.
Q. Are there any signs that terrorism might have been involved?
A. No group is known to have claimed to have destroyed the plane. Beyond that, not enough is known to speculate.
Q. If the plane had a major malfunction, wouldn’t the pilots have called for help and sent distress signals?
A. Pilots have a mantra for setting priorities in an emergency: aviate, navigate, communicate. The first priority is to fly the airplane. Telling air traffic controllers on the ground what is going on comes third, since doing so is unlikely to instantly yield any help with the crisis in the cockpit, whatever it may be. If the pilots are fighting to keep the plane aloft, they may not have time to use the radio.
Q. Could one of the pilots have crashed the plane deliberately?
A. It’s been known to happen: The crashes of an EgyptAir flight from Kennedy International Airport in 1999 and a SilkAir flight in Indonesia in 1997 were attributed to intentional acts by cockpit crew members. But nothing is yet known publicly to suggest that that happened on the Malaysia Airlines flight.
Q. Have other planes disappeared in this way in recent years?
A. There is no record of big planes simply disappearing, though they may take some time to find. A few pieces of debris from Air France Flight 447 were spotted floating in the Atlantic the day after the plane crashed in June 2009, but it took five days to find most of the wreckage. Small aircraft may be missing for much longer if they go down in remote areas. Steve Fossett, the daredevil adventurer who flew around the world solo in a plane and set records in a balloon, took off in his private plane in Nevada on Sept. 3, 2007, and his remains were found in October 2008.