Poised for Takeoff : High-Precision Navigation Becoming Aircraft Standard
In the pre-dawn hours of Sept. 1, 1983, Korean Air Lines transpacific Flight 007 strayed off course and deep into Soviet airspace over Sakhalin Island.
A Soviet fighter pilot, apparently unable to see that the airplane was a commercial one, fired a single missile. The Boeing 747 went down and all 269 people aboard died in one of the Cold War’s worst tragedies.
Almost immediately, President Ronald Reagan cut short bureaucratic infighting over the incident and announced that, to prevent another such disaster, a U.S. Defense Department satellite navigation system then under development would be made available free of charge to the world’s airlines.
Today, the 24-satellite network known as the Global Positioning System is in orbit and helping thousands of motorists, hikers and others figure out where they are with unprecedented precision.
And in May--while aviation regulators wrestle with details and the U.S. and foreign governments fret about the security implications--the original goal of enhancing the safety and lowering the cost of transoceanic flight will come an important step closer. Boeing’s 777, the world’s first aircraft with GPS as standard equipment, will roll off the assembly line.
“The guys that fly long range are all excited about it,” Boeing Vice President Lawrence W. Clarkson said during a recent visit to Tokyo. “Boeing is very confident that GPS will be the navigation system of the 21st Century.”
The 24-satellite system was completed in 1993 and approved by the federal government last year for use in civil aviation navigation. Research continues into its use for precision landings. It is expected to be widely used for transoceanic flights by 1997.
European aircraft maker Airbus has already installed GPS systems on some A340 long-range jets now used for flights over the Atlantic. These and other GPS-equipped planes will at first use the system as a backup to keep pilots informed of their exact positions when planes are beyond the reach of radar and land-based navigational aids.
Once installed in large numbers of aircraft, GPS could save travelers time and money, save airlines billions of dollars a year and make air travel less risky overall.
“Once GPS is fully operational it could save the world’s airlines well into the billions of dollars per year in lower fuel and labor costs,” said Chris Chiames of the Air Transport Assn., which represents the U.S. airline industry. “I’ve seen some estimates of anywhere from $3 billion to $5 billion per year on a worldwide basis.
“On the technology side . . . we think it offers one of the biggest breakthroughs, not just in air traffic control but in safety for airlines and their passengers.”
Magellan Systems of San Dimas, Trimble Navigation and Ashtech of Sunnyvale and ESRI of Redlands are the leading suppliers of equipment for communicating with the GPS satellites.
GPS is already used by motorists to augment the satellite signals with information from land-based broadcasts to show a vehicle’s precise location on a video screen map. Portable receivers are in use in some small private aircraft to double-check latitude and longitude. Hikers can buy a hand-held device for $500.
But one of the biggest payoffs is thought to lie in long-range air travel, since the inaccuracies of conventional navigation techniques require that flight planners keep planes hundreds of miles apart--sending them on longer or less desirable routes and swallowing up far more time and fuel than necessary.
To reap the big savings ultimately expected, most aircraft will need to be equipped with GPS navigational ability, which calculates an airplane’s location by taking precise readings of the position of and distance to at least four GPS satellites. The readings are based on signals emitted by the satellites, including time signals from on-board atomic clocks said to lose only one second every 160,000 years.
Calculations of an aircraft’s position by civil aviation users of GPS will be accurate to within 109 yards at least 95% of the time, and to within 328 yards at least 99.99% of the time, according to Amy E. Bellay, a spokeswoman for the U.S. Federal Aviation Administration, who was in Tokyo recently to promote GPS technology at an aerospace show.
The U.S. military can use the system with greater accuracy, a capability that will remain proprietary.
The technical effectiveness of GPS for commercial flight has been proven in a variety of tests. It has been used for inter-island flights in Fiji since 1993, according to Fred Laird, senior FAA representative at the U.S. Embassy in Tokyo.
More efficient routing will be one major benefit, as flights can be safely crowded together to take advantage of the shortest paths and most favorable winds. Travel times across the Pacific, for example, may be shortened by as much as an hour, Bellay said.
Today’s computer-assisted oceanic navigation--used by the ill-fated KAL Flight 007 and still in common use--depends on precise knowledge of an airplane’s position at takeoff. Measurements from a laser gyroscope and other instruments are then fed into an on-board computer, which calculates changes in the airplane’s position as it flies.
Such calculations, however, have a margin of error of up to 1.1 miles for each hour of flight. This means that after a 10-hour flight outside the reach of land-based navigational aids, the position could be off by 11 miles.
Because of such inaccuracies, flights often are not allowed to take the most ideal route between two points. Airplanes on identical routes must be kept at least 15 minutes apart, and parallel flights at least 69 miles apart, explained Takashi Arima, an FAA official at the U.S. Embassy in Tokyo.
Airplanes also waste significant time and fuel when they overtake slower aircraft, and must take wide detours because positions are not precisely known, Laird said.
The FAA hopes that with GPS, space between flights can be safely cut to just five minutes from the current 15, Arima said. Separation between parallel paths would also be reduced, he said. This would enable many more airplanes to take the most direct routes.
In addition to its advantages for long-distance flights, GPS augmented by ground-based navigational aids should make precision landings possible even in extremely poor visibility.
One noteworthy test of GPS, says Richard Arnold, the FAA’s navigation systems director, Continental Express’s use of it flying into mountainous Aspen, Colo., in the winter of 1993-94. “Continental told us they carried 50,000 more passengers than they would have without it,” Arnold said.
GPS made it safe to land in poorer visibility than would otherwise have been possible, he explained.
Navigation using GPS should also eliminate the kind of massive miscalculation of position--believed the result of pilots’ navigational error--that apparently led to the KAL tragedy, said Hiroki Takeda, deputy director of radio engineering for Japan’s Civil Aviation Bureau.
One of the biggest stumbling blocks to greater international use of GPS in civil aviation is the reluctance of many countries to become dependent on a system owned and controlled by the U.S. military. The Defense Department can turn off the satellites or encode the signals in time of war to shut out an enemy. There also is fear that the United States might someday decide to charge fees for using the system.
Chiames stressed that stronger assurances about access to the system are needed to make foreign users comfortable with it.
He said that foreign users worry about what would happen “if there’s another Desert Storm . . . and (Defense) shuts off or scrambles the system in the name of national security.”
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Transoceanic Navigation by Satellite
The system of 24 Global Positioning System satellites now orbiting the Earth will make aircraft navigation dramatically more accurate, enhancing public safety, shortening flight time and saving billions of dollars in fuel annually. Calculations of position will be accurate to within 328 yards at least 99.9% of the time. Today, to allow safety margin for navigating inaccuracies, planes on identical routes must be kept at least 15 minutes apart while those on parallel routes must be at least 69 miles apart. The GPS system will slash those distances by as much as two-thirds, enabling far more aircraft to travel the shortest, most direct routes using the most favorable winds.
1. By receiving signals from at least four Global Positioning System satellites, an airplane crossing the Pacific can determine its exact position.
2. Information on aircraft will be relayed to traffic controllers by radio or through a communications satellite such as Japan’s MTSAT.
3. More precise information on the location of aircraft will enable controllers to both lessen the distance between aircraft on identical routes and narrow the distance between those on parallel paths.
