In the North Atlantic Track System (NATS) alone, the heaviest traveled oceanic sector in the world, 1,200 crossings on average are made every day, 600 in each direction. According to Nat Iyengar, formerly with World Airways and currently a safety pilot in a major corporation's flight department, the amount of traffic encountered in the NATS on a typical crossing has to be seen to be fully appreciated.
“The traffic is so dense that on a clear night you can easily count up to 50 aircraft above, below and on adjacent tracks during your crossing,” he said. “At any given time, the lights of as many as a dozen are visible around you. It's like a six-lane highway: Interstate 95 at rush hour!”
Thus, when an aircraft proceeds out over the North Atlantic, vertical, lateral and longitudinal separation must be precisely maintained for everything to work safely and efficiently. The responsibility for this interaction falls squarely on flight crews (and to a lesser extent on controllers hundreds of miles away).
Depending on projected traffic levels, the NATS consist of as few as four and can exceed 13 parallel tracks, all temporary routes “built” twice a day across North Atlantic airspace, their position determined by prevailing winds. (That is, the tracks are shifted either north or south to take advantage of the most favorable winds.) Eastbound tracks are laid out by Gander Area Control Center (ACC) and apply between 0100 and 0800 UTC (at 30 deg. west longitude), their westbound counterparts by Shanwick ACC, applying between 1130 and 1900 UTC (also at 30 deg. west).
Within the track system, traffic flows only one way, depending on the time of day, i.e., easterly at night, westerly during daylight hours. Typically, the “core” tracks will lie within the confines of Gander and Shanwick airspace, but when the system is built up to accommodate peak traffic loads, the northernmost track can nudge into Reykjavik/Shanwick controlled airspace and southernmost into New York/Santa Maria (Azores) territory.
Flight levels on the tracks are separated vertically at 1,000-ft. levels (RVSM was introduced in 1997, the first region in the world to receive it). Eastbound tracks consistently operate between FL 320 and FL 400, while westbound tracks are commonly set between FL 310 and FL 390. Currently, tracks are separated laterally by 1 deg. of latitude at each 10 deg. of longitude (as standard in Minimum Navigation Performance Specification airspace), resulting in distances between tracks varying between 50.5 nm and 60 nm. Meanwhile, longitudinal separation of 10 min. is maintained by assigned Mach number.
Sometime between 2015 and a future date to be determined, separation will be reduced to one-half degree latitude throughout the Organized Track System (OTS) to allow more capacity (i.e., additional tracks), ratcheting down distance between adjacent tracks to between 25.25 nm and 30 nm — and demanding even tighter adherence to procedures and required navigation performance. Likewise, longitudinal separation is scheduled to be reduced by 50% to 5 min. within the same time frame. We'll elaborate more on these changes and the equipage mandate necessary to meet them later on in this report. (But understand now that there is a big change on the near horizon in how aircraft will need to be equipped in order to operate on the NATS and other North Atlantic MNPS airspace.)
Out in the Pacific region on the Pacific Organized Track System (PACOTS), lateral separation between tracks has been reduced from 100 nm to 50 nm for aircraft operating between FL 290 and FL 410 with navigation equipment certified to RNP-10 accuracy and 30 nm for those meeting the RNP-4 standard plus equipage and approval for Controller Pilot Data Link Communication (CPDLC) and Automatic Dependent Surveillance-Contract (ADS-C).
The PACOTS are generally laid out south of the Northern Pacific published route structure, but depending on winds they may merge (i.e., if winds require that the PACOTS be moved north). Also traversing the vast Pacific Ocean are the Central Pacific published routes between the U.S. West Coast and Hawaii and the Southern Pacific published routes between the West Coast and New Zealand and Australia. Finally, an organized track system runs between Japan and Hawaii but is rarely traversed by business aviation.
A related issue that especially concerns business aviation operators flying in oceanic airspace, especially on the track systems, is the ongoing tally of gross navigation errors (GNEs) and large height deviations (LHDs) attributed to general aviation. Per capita, or as a percentage of usage, general aviation error totals have shown little improvement over the last decade. This is a particular concern to both regulators and the business aviation community, given the forthcoming reduction in oceanic separation standards.