Technology Tracks Transatlantic Traffic
Have you ever wondered why there aren’t more collisions in airspace that has no radar coverage? Like most passengers, you probably haven’t given much thought to the complexities of transatlantic air travel. In 2007, more than 425,000 flights crossed the Atlantic—that’s 1,164 aircraft crossings each day. Growth rates are projected at 5 percent to 10 percent annually (depending on the economy) for many years to come.
You’d be amazed at how much goes on behind the scenes to get you across the pond and back again. It’s an intricate process that has evolved into a safe and efficient operation after years of technological innovation and careful oversight.
Imagine a superhighway in the sky, complete with entry and exit ramps, that links New York to London: That’s exactly how the Organized Track System (OTS) and the North Atlantic Track System (NAT Track) function. An enormous number of aircraft use these systems daily, so in order to keep them from running into each other, rigid guidelines have been designed and implemented.
Staying on track
For years, the majority of transatlantic air traffic traveled between two high-density population centers: the United States and Great Britain. But today, carriers from across Europe fly to and from destinations all over North America. To get there, aircraft usually fly in the NAT Track. These tracks are published twice a day by oceanic planners, and they frequently change position to take advantage of the prevailing jet stream and great circle routing. Westbound tracks operate during the day and are labeled with the letters A–F. Eastbound tracks (labeled S–Y) are active during the evening, since many Europe-bound flights take off late at night from U.S. airports and arrive at their destinations in the early morning.
The tracks are 29,000 to 41,000 feet up and have specific entry and exit points, called waypoints, which act somewhat like freeway on- and off-ramps. Aircraft enter the tracks according to dedicated time slots that act much like the stop lights that feed traffic smoothly onto overcrowded highways. Pilots must have an entry time slot (clearance) from Oceanic Air Traffic Control (ATC) before entering the NAT Track system. It is not mandatory to use the OTS to cross the Atlantic, but priority is given to those aircraft that do.
Keeping your distance
Because a large portion of the airspace over the Atlantic is not covered by ground-based radar, aircraft traveling inside it must be remotely monitored. (This concept is all too familiar now, as the remains of Air France flight 447 were not found for days because the plane was not on radar and its exact location at the time of crash was unknown.) Pilots must report their position to ATC at each waypoint to check their progress against the ATC-filed flight plan. These position reports can be made through a satellite data link or high-frequency radio. Any excessive deviation from the plan must be corrected in order to keep safe distances between aircraft.
To maintain a modest margin of safety, the tracks are constructed about 60 miles (one degree of latitude) apart and are separated vertically in thousand-foot altitude blocks. Entry times at ingress waypoints, assigned altitudes and planned speed (mach number) are three of the variables on which the system relies. Aircrews must adhere to these guidelines if they wish to traverse the oceanic airspace.
Sharing the airspace
To use the NAT Track system, aircraft and pilots must be certified to operate in the MNPS/RVSM (Minimum Navigation Performance Specifications/Reduced Vertical Separation Minimum) airspace. Aircraft must have extremely accurate navigation equipment in the form of altimeters, autopilots and a host of other required equipment. All aircraft have to be able to maintain a specific altitude with high accuracy and not deviate from their assigned altitude or ground track without prior approval from ATC.
RVSM is intended to allow a greater number of aircraft to use the airspace more efficiently. Previously, aircraft were separated by 2,000 feet vertically, but the limit has since been reduced to 1,000 feet, as noted above. Not only does this save pilots fuel as they operate more closely to their optimum altitudes, but it also allows more aircraft to operate in the space at any given time.
Given all the moving parts of the NAT Track system, what happens if there’s a problem? Visualize a five-lane freeway at rush hour. All the cars are traveling at the same speed with the same distance between them. Suddenly, a vehicle three cars ahead of you in the second lane from the median blows a tire and starts to change lanes, heading for the right shoulder. Naturally, all the cars in the vicinity start to slow down to avoid the affected car, and a backup starts to build. This same scenario can be applied to the NAT Track system—but with a twist.
Let’s say a 777 on the C track at flight level 350 has a problem and can’t maintain altitude on just one engine. The pilot has traffic on either side (tracks B and D), as well as above and below (at FL360 and FL340). Traffic backup is not acceptable, because planes must maintain a minimum speed to stay airborne. In this scenario, the pilot would immediately transmit his problem over the common frequency, and, depending on which direction he was going in, would turn 45 degrees off-track, then turn parallel (15 miles from track) to get out of the traffic flow.
Next, he would either climb or descend 500 feet to avoid conflict with the other aircraft in his vicinity. Due to the nature of this particular emergency, the 777 would descend and look for an emergency landing field. During the “drift down” procedure, the pilot would assess his situation while looking for a clearance. As soon as he dropped below 29,000 feet, he would be clear of the track system and could accept more direct routing.
Thanks to the dedication and cooperation of the agencies tasked to administer the OTS, we have a system that provides millions of passengers with a safe and efficient way to cross the Atlantic by air. There will be further challenges as we increase the number of daily flights to accommodate our growing population, but well-considered procedures and the dedication of thousands of professionals will bring continued success.
CHRIS COOKE is a pilot with a major domestic carrier. He can be reached at firstname.lastname@example.org.