Air traffic controllers lost contact with the jetliner at the junction of several international air traffic control regions—the kind of fringe location where radar coverage is known be spotty
Modern technology tends to evoke feelings that Big Brother is always watching. The unsolved mystery of Flight 370, however, makes clear that Big Brother does not exist in the sky—long-haul passenger aircraft are at the mercy of a coordinated air-traffic control system that relies on a series of handoffs across independently monitored “flight information regions” to get passengers safely to their destination. Aircraft are equipped with technology that automatically communicates certain information, but this coordination works best there is regular communication between the cockpit and air traffic control.
As defined by the United Nations’ International Civil Aviation Organization, a flight information region is an expanse of airspace within which an aircraft receives basic levels of air traffic service, including information about weather and potentially conflicting air traffic. Larger countries are typically divided into multiple regions, whereas some small countries’ entire airspace fits in a single region.
The area where air traffic control lost contact with Flight 370 the morning of March 8 as it flew 239 passengers and crew from Kuala Lumpur en route to Beijing is a patchwork of regions controlled by different countries. For nearly two weeks, investigators from 26 countries have helped Malaysia look for the plane without success.
Although it is difficult to trace Flight 370’s route exactly because the aircraft’s transponder and secondary radar went silent after about an hour into its journey, several sources report the 777 turned westward from its route to Beijing near the border of several different flight information regions. These regions are maintained by Malaysia, Singapore, Thailand and Vietnam, respectively. Authorities learned several hours after the fact that Flight 370 had changed its heading to fly across northern Malaysia toward the Strait of Malacca. The latest reports about the aircraft’s fate revolves around large pieces of debris reportedly spotted via satellite imagery in the southern Indian Ocean, thousands of kilometers from the aircraft’s original destination. Search teams have yet to confirm whether the objects in the images are from the China-bound flight, however.
Radar coverage at the fringes of flight information regions can be spotty due to radio wave attenuation—that is, loss of signal intensity—that can be exacerbated by rough terrain, says Jason Day, an instructor in Arizona State University’s Aviation Program and a former airline pilot. “Once you get on the fringe, clouds can also mess with the signal,” he adds.
Military aircraft might fly along the edges of two flight information regions to provide stealth, but there are few legitimate reasons for a commercial airline pilot to do this intentionally, Day says.
Air traffic control centers hand off responsibility for flights as aircraft move through these regions and from one region to another. This is analogous to the way cell phone towers pass along mobile phone users as they migrate from one area of coverage to another. In aviation, a pilot generally acknowledges such a transition by saying “good night” or “goodbye” to the previous air traffic control center. Several reports indicate the last verbal communication with air traffic controllers from Flight 370—less than an hour after takeoff—was, “All right, good night.”
Shortly afterward, civilian air traffic controllers lost contact with Flight 370, although military radar reportedly detected the aircraft hours later, hundreds of kilometers off course. Air traffic controllers on the ground are unable to determine whether someone onboard the 777 purposely severed communications or this was done in reaction to a fire or other catastrophe.
Pilots control much of the aircraft directly from the cockpit, including cabin pressure, the flow of oxygen, the flight management system computer and transponder signal, which broadcasts the aircraft’s altitude, direction and air speed. The Aircraft Communications Addressing and Reporting System (ACARS), which transmits information from the flight management system to air traffic controllers, is integrated directly into the computer and runs in the background. A crewmember could effectively turn it off by shutting down the flight management system, according to Day. “The only way someone on the ground would know that you’d made changes to the flight management system is by studying the info broadcast by the ACARS,” he says. If the ACARS is shut off, air traffic control would not immediately know whether someone had programmed new instructions into the flight management system.
Pilots can fly without their flight management system under certain circumstances—an electrical fire requiring power to that circuit be turned off or the system is providing erroneous readings, Day says. If the system “goes haywire,” the pilots might shut it down and navigate using raw data sent to their aircraft by short-range radio signals, a beacon or an instrument landing system, depending upon where the aircraft is in relation to its landing site.
The aviation industry has for the past several years been developing technology to address the inability of air traffic controllers and the airlines themselves to remain in constant contact with aircraft on long flights over the ocean. One of the more promising innovations is satellite-based automated dependent surveillance–broadcast (ADS–B) equipment. ADS–B relies on communication between global positioning system (GPS) satellites and transponders placed on board aircraft to inform pilots, other aircraft and air traffic controllers about an aircraft’s location, identity, speed and altitude. ADS–B continuously collects and transmits information, whereas radar emits electromagnetic waves at regular intervals.
The U.S. Federal Aviation Administration (FAA) has been pushing adoption of ADS-B as part of the agency’s Next Generation Air Transportation System program for years, although the technology is still not mainstream. The FAA is hoping ADS–B “will move air traffic control from a radar-based system to a satellite-derived aircraft location system,” according to the May 28, 2010 Federal Register, which states aircraft operating in most U.S. airspaces must have ADS-B by 2020. (pdf)
Aircraft operating in European Union airspace must have ADS-B by 2017, and new aircraft built beginning 2015 must be equipped with the technology. (pdf) Several other countries, including Australia, Singapore and Vietnam, have already begun to require certain aircraft to have ADS-B when flying in certain parts of their airspace.