The National Route Program was developed as a way for participating airlines to fly routes of their choosing based on weather conditions. The only requirements are that they fly standard routes within 200 miles of their departure and destination airports. This ensures an orderly traffic flow during climb and descent. NRP is generally only used for flights over 1000 miles.
When the aircraft are west of Chicago, the western US airspace has a grid pattern of blandly-named, unpronounceable navigation fixes to facilitate flexibility in NRP flight planning. These are referred to as High Altitude Redesign (HAR) fixes. Under NRP rules, airlines may file these HAR fixes to help them make the most out of a headwind or tailwind and/or to avoid thunderstorms or military training airspace. These flights are conducted with advanced GPS navigation, and none of these fixes require any ground based facilities. Some airlines use these fixes more than others. Many choose to fly coast to coast, clearly not in a straight line, under NRP rules, and use only ground based VORs the whole way, keeping the same zig-zagging routes that NextGen will supposedly solve by eliminating VOR navigation. Our current system appears to meet the needs of airlines attempting to save money by flying fuel efficient routes of their choice.
From an ATC standpoint, any aircraft with "NRP" in the remarks of their flight plan should not be given any shortcuts, unless requested by the pilot, and if we have to change their altitude or route due to other conflicting traffic, we are supposed to return that flight to its requested route and altitude as soon as possible.
So let us review a few flights that fly from Boston to San Fransisco in the mid-morning everyday.
UAL719 B757 (United)
Departed Boston at 8:20am.
Filed NRP over Sault St. Marie, then to Minneapolis, airways to Rock Springs, WY, and then Coaldale, NV for the arrival.
Time enroute, with some vectors by Oakland Center: 5:30
AAL183 B757 (American)
Departed Boston at 8:26am, Six minutes behind United.
Filed NRP over Canada in a similar fashion as United, but only as far north as Green Bay. They used a few of the HAR fixes (KP87G, KP81A, KD66S, and KU54M) to connect Green Bay with Medicine Bow, WY and Myton, UT.
After getting a few vectors, as well, approaching SFO, they arrived 14 minutes after United for a total of 5:38.
VRD351 A319 ("Redwood" Virgin America)
Departed Boston at 8:59am, 33 minutes after American.
They filed over Canada as well, but not quite as north as Green Bay. They used 6 HAR fixes to get to Delta, UT. They were also not vectored quite as much by Oakland Center, but given a few wild turns by the approach control.
Total time en-route: 5:40.
JBU631 A320 (jetBlue)
Departed Boston at 9:46am, 47 minutes after the Virgin.
They joined the Canadian party as well, but instead of flying over Utah and approaching SFO from the east, they chose to stay north of everyone else, flying over Crazy Woman, WY (everyone loves that VOR for some reason) to Reno, NV and then joined the arrival from the north. They started south, and ended up north.
They received a big vector to final by approach, and still matched AAL183 with a time en-route of 5:38.
For more perspective, lets look at UAL719 from the day before:
They filed over Syracuse and remained south, compared to the next day, until Utah. However, they either didn't request NRP rules, or they requested a shortcut, because they were cleared direct ONL (O'neill, NE) while climbing out over MHT, and then Cleveland Center gave them direct Coaldale, NV. They were given a brief vector over Nevada, but the most straight-in approach. Gotta love Saturday morning. Still, the flight took 5:45.
Lesson: Using "old-fashioned" VOR navigation doesn't always hinder a flight and force the airlines to lose money. Flying direct routing doesn't always mean the fastest flight time using the least amount of fuel.
Thanks as always to Flightaware.com!
Till next time....