Saturday, April 26, 2008

North Atlantic Tracks

North Atlantic Tracks (NAT) are about jet stream, a fast narrow air currents found in the atmosphere about 10 kilometers above the Earth's surface. In northern hemisphere, jet stream travels in a west-to-east direction.

North Atlantic Tracks are heavily-traveled air corridors that stretch from the northeast of North America to western Europe. Unlike stationary land-based airways, the aviation authorities (Shanwick and Gander Oceanic Centers), collectively, relocate these 'tracks' on a daily basis. In so doing, Europe-bound aircrafts traveling on the NAT can save fuel by taking advantage of the strong tail winds generated by the jet stream and westbound traffics can avoid the strong head wind created by the same narrow jet stream. Because strong jet stream causes difference in ground speed, for any given transatlantic city pair, westbound flights usually take longer than their eastbound counterparts.

Aside from supply and demand, airlines' flight schedules are planned around European airports' nighttime closings and landing restrictions. This in turn has an effect on NAT traffic pattern. For NAT, westbound traffic is heaviest during daylight hours and eastbound tracks become crowded during night hours.

There are 5 or 6 tracks in each direction at any given time. Alphabetical letters are used to identify individual tracks, which are kept 60 miles apart from one another. There are approximately eight waypoints in each track.

Each track starts and ends with two named waypoints, linking it to the land-base airways at either side of the Atlantic. Other intermediate waypoints along a track are identified using earth's coordinates (latitude-longitude pairs). All tracks have waypoints along the following longitudes: 50°W, 40°W, 30°W, and 20°W. Pilots are required to project and report their estimated time of arrival (ETA) at the track's entry point as well as the ETA at each waypoint while traveling along these tracks.

For decades, High Frequency-Single Side Band (HF-SSB) has been used exclusively for opened-waters air-to-ground communication. In recent years, satellite-based air-to-ground communication equipment are widely used throughout the airline industry. Today, aircrafts with advanced ACARS and CPDLC equipment conduct air-to-ground communication (position reporting, ATC routing, flight plan, weather information, etc.) through satellite-based digital data links. Although HF-SSB voice channels are still in use, the voice traffic in these channels is significantly less in comparison.

Active NAT is available at https://www.notams.jcs.mil/common/nat.html. Aside from the waypoints of individual active tracks, the webpage has other information such as the list's update time, effective period, flight levels, remarks, etc.

With no radar coverage in the Atlantic, aircraft separation rules are strictly enforced in NAT until aircrafts again come within the range of land-based radars. In general, aircrafts on the same track are kept separated by 10 minutes time interval at same flight level or are kept at 1000 feet vertical distance.

In pre-flight planning, an active transatlantic track is identified for the flight and the selected track then becomes a part of its flight plan to be filed with the aviation authority, e.g. FAA. As a routine precaution, many in-flight emergencies are also considered and contingencies are hashed out before the actual Atlantic crossing.

Pacific Organized Track System (PACOTS) is NAT's counterpart over the northern Pacific. They comprise a set of airways linking Japan, Southeast Asia, Honolulu and the mainland US.

Comments?

2 comments:

Unknown said...

Note sure WHY this still doesn't have any comments. Thanks for putting it up, very informative!

Anonymous said...

Very informative indeed, thanks!