Why Flights Will Continue to Drop off the Radar - for Now (en anglais seulement)

For most people, flying is an act of faith. Take a seat, place your trust in the skill of the pilots, the quality of the aircraft and the diligence of those who maintain them, and shut out thoughts of anything less than a happy landing. But tragedies such as the as-yet-unexplained June 1 crash of an Air France Airbus A330 into the sea off Brazil, which killed 228 passengers and crew, crystallize all our old fears. And they occasionally highlight things few travellers had ever previously worried about. Like the fact that transoceanic flights disappear from radar a half-hour after clearing land, leaving air traffic controllers to only guess at their whereabouts for large portions of the voyage.

In an age where your cellphone can track your location - and that of your friends - within a couple of feet, and your car's dashboard navigation system can plot every twist, turn and rest stop of a cross-country trip, it seems inconceivable. But while airline pilots know their aircraft's location thanks to satellite GPS, that information isn't always readily available to those back on the ground. Traditional radar can only reach about 320 km offshore because of the curvature of the earth. And the wide expanses of the ocean make it difficult for planes to share their position. Radio coverage can be patchy, depending on distance and weather, and transmission via satellite is too costly for constant use. (Air France, like many carriers, gets bulletins from on-board computers about mechanical issues that crop up during flights, so it can be ready to fix them once the plane lands. In the case of Flight 447, those messages - sent directly to the airline's headquarters - were the first, and as it turned out only, indication of trouble.)

So, for all of society's high-tech advances, the way planes fly across oceans has barely changed in half a century. As they approach the coastline, aircraft move into designated tracks, high-altitude express lanes spread across the sky. Once in track, planes maintain a strict separation - 80 nautical miles longitudinally, 60 nautical miles laterally, and 1,000 feet in altitude. Their true positions are relayed back to air traffic control when they pass fixed points along the route, usually about once an hour. The rest of the time, controllers have only a vague notion of their progress, based on factors like airspeed, the prevailing winds, and pilots' estimated time of arrival at the next checkpoint.

It's a system that emphasizes safety - each evening along North America's eastern seaboard, for example, hundreds of Europe-bound jets trace basically the same route out over Newfoundland and across the North Atlantic without incident - but at a cost. Not everyone can fly at the most efficient altitudes, and changing tracks to avoid storms or rough air while maintaining separation can be a laborious process. Keeping everyone on the same path also makes many flights more circuitous than necessary.

And despite the ubiquity of GPS technology, it appears change will be slow in coming. Major members of the International Civil Aviation Organization (ICAO), the UN body that governs the world's skies, signed a declaration in early April calling for a "rapid" shift to performance-based navigation - using satellites instead of ground-based monitoring to help make flying more efficient and "green." But the timetable for implementation remains vague. The United States has so far deployed the GPS technology only in parts of Alaska and southern Florida (the first test will be a Paris-Miami flight June 10) and the Federal Aviation Administration is still lobbying Congress for the tens of billions it needs to set up a national network.

Nav Canada, the private sector body responsible for air traffic over this country, debuted its Automatic Dependent Surveillance-Broadcast (ADS-B) system this past January, providing coverage for the skies over Hudson Bay. Previously, the 35,000 flights a year that crossed the region were out of tracking range and had to maintain oceanic separation distances until much further south. Now those equipped with GPS beacons automatically transmit their position, altitude, speed and other data to five ground stations that have been placed around the shores of the bay to relay the information to air traffic control. "It's better than radar," says Jeff MacDonald, NavCan's manager of air navigation systems. "This updates once per second. It takes radar four seconds to do its 360-degree sweep." As a result, ADS-B tracked flights can now move to the same separation - just five miles - they have in radar zones, climbing and descending faster, saving an estimated 18 million litres of fuel a year. The next phase will see Nav Canada and its Danish counterpart set up more of the fridge-sized ground monitors in Labrador and Greenland, providing coverage for part of the North Atlantic.

But until somebody figures out how to anchor the relay stations in the open sea - they must be fixed points to work - or develops a different GPS-monitoring technology, vast zones of the world will remain "off the grid." A reminder that even as it gets smaller, the world remains a frighteningly large place.

See also Aviation.

Maclean's June 22, 2009