pole and made its 8,000th polar flight in April 2008, demonstrating the dramatic rise of air traffic over the North Pole. United is not alone. Thirteen carriers flew polar routes for a combined total of almost 7300 polar flights in 2007, an increase of nearly 2000 flights from the prior year.

Why polar routes? As Stills indicated, aircraft can cost hundreds of dollars per minute to operate. Polar routes reduce the time in flight. As an example, United Flight 829 on a polar route took 14 hours and 32 minutes to fly from Chicago to Hong Kong in March 2006. It carried 316 passengers and 5000 pounds of additional cargo. If the same plane had flown the best available non-polar route to Hong Kong, due to the greater headwinds it would have required 15 hours and 41 minutes, reducing the passengers to 246 and removing all 5000 pounds of extra cargo. So the polar routes allow United Airlines to avoid the strong wintertime headwinds and decrease travel time, and therefore transport more passengers and cargo, thus offering a more economical and convenient service to its customers.

Federal regulations require flights to maintain communications with Air Traffic Control and their company over the entire route of flight. United relies on SATCOM, which is communication via satellites in geosynchronous orbit (located about 22,000 miles above the equator). Aircraft lose the ability to communicate with these satellites when they go above 82 degrees north latitude (within the circle shown toward the center of Figure 5.1). In this region, aircraft communications are reliant on HF (high-frequency) radio links.

Strong solar activity causes HF radio blackouts in the polar region. Occasionally the Sun emits a shower of high-energy protons and other ions (called a solar energetic particle (SEP) event). When the protons hit Earth’s outermost atmosphere (called the ionosphere), they increase the density of ionized gas, which in turn affects the ability of radio waves to propagate.1 HF radio frequencies in the polar regions are particularly affected because the solar protons can directly reach the ionosphere in the polar cusp of Earth’s magnetic field. The radio blackouts over the poles are called polar cap absorption (PCA) events. When a solar event causes severe HF degradation in the polar region, aircraft that are dependent on SATCOM have to be diverted to latitudes below 82 degrees north so that SATCOM satellite communication links can be used. United Airlines currently utilizes the NOAA Space Weather Prediction Center (SWPC) space weather scales and alerts to plan upcoming flights and to instruct planes in transit to divert from polar routes.

PCA blackouts can last up to several days, depending on the size and location of the disturbance on the Sun that triggers them. For example, between January 15 and 19, 2005, five separate x-ray solar flares occurred that produced radio blackouts of R3 intensity. (The radio blackout scales are shown in Figure 5.2.) One of the alerts, shown in Figure 5.3, tied the expected intensity of the blackout to the X1.2 strength of the solar x-ray flare.2 For 4 consecutive days, flights from Chicago to Hong Kong could not operate on polar routes. The longer non-polar routes required an extra refueling stop in Anchorage, Alaska, which added delays ranging from 3 to 3½ hours. In total, 26 flights operated on less than optimal polar routes or non-polar routes. Increased flight time and extra landings and takeoffs increase fuel consumption and cost, and the delays disrupted connections to other flights.

Stills noted, “Ten years ago United had no reason to take space weather into consideration, but now it is something that United Airlines actively monitors, and we change and enhance our policies and procedures as more information and data become available.”

Stills indicated that United Airlines already considers in its flight planning the information and data it receives from SWPC, such as D region absorption and polar cap absorption that affects HF communications. United is also interested in K index geomagnetic status and x-ray intensity, and has just mandated that its meteorological team monitor proton flux with energy levels of 10 MEV and greater and 100 MEV and greater.

The availability of real-time solar flare monitoring and radio blackout alert services allows the airline industry to use polar routes safely. In response to an audience question, Stills indicated that accurate, high-confidence forecasts would also be useful: “Typically … the planning … for international flights … is done 2 to 3 hours in advance of the actual operation. But the infrastructure and support for an airline operation, typically things like which aircraft is assigned to, say, the Chicago-Hong Kong flight tomorrow, … is done a day in advance. The crews are assigned well in advance. They have duty time limits. All of those things come into play.”

“So it is extremely important to have an accurate prediction,” Stills emphasized. “It is very important to have it in a timely fashion and as far in advance as possible. Clearly we realize there are limitations, but to have from an infrastructure standpoint a forecast, say, 6 to 10 hours in advance would be wonderful, but from an operational



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement