GPS technology helps Hanscom improve air traffic management

by Patty Welsh
66th Air Base Group Public Affairs

7/21/2015 - HANSCOM AIR FORCE BASE, Mass.  -- As the 20th anniversary of Global Positioning System, or GPS, technology is this month, the Aerospace Management Systems Division here explains how the technology enables their work enhancing performance and safety of air traffic management.

"The biggest improvement that GPS technology brought to air traffic management is that the aircraft itself can reliably know its position rather than relying on circa 1940s ground-based nav(igation) aids," said Ben Brandt, MITRE senior technical advisor to the Division's Communication, Navigation, Surveillance/Air Traffic Management or CNS/ATM program.

In the United States the transition to GPS-based navigation is a central tenet of the Next Generation Air Transportation System, or NextGen. NextGen is a massive initiative between federal partners to modernize America's air transportation system, and according to documentation developed by the Federal Aviation Administration, it involves a shift to satellite-based and digital technology. The Aerospace Management Systems Division is the main Air Force conduit for participation in NextGen.

The CNS/ATM program's main focus is to ensure Air Force aircraft can operate in this NextGen airspace. Program personnel accomplish this by tracking and contributing to civil aviation standards forums, interpreting the standards into a set of requirements that can be leveraged by any Air Force aircraft program, providing subject matter expertise to aircraft programs in design or development and ultimately conducting an independent assessment of a program's implementation to ensure the aircraft can safely operate in the airspace with civilian aircraft.

GPS technology helps with that interoperability.

The accuracy provided by GPS allows more aircraft to fit in the same amount of airspace by reducing the space between aircraft while maintaining the same level of safety, and enables Performance-Based Navigation. PBN is described on the FAA website as a series of "new routes and procedures that primarily use satellite-based navigation and on-board aircraft equipment to navigate with greater precision and accuracy. PBN provides a basis for designing and implementing automated flight paths, airspace redesign and obstacle clearance."

"PBN is a primary focus area of NextGen," said Brandt.

For the CNS/ATM office, a core objective is to assess military GPS receivers to ensure they can provide the necessary and appropriate information to support capabilities such as PBN.

"The ultimate goal of our GPS-related efforts is to demonstrate that the performance of our legacy and new M-Code GPS receivers can meet the performance necessary to be  interoperable with civilian air traffic without requiring our Air Force aircraft to equip with both civil and military GPS receivers," said Col. Joe Leonard, Division senior materiel leader.

Another key tenet of Hanscom's work that relies on GPS technology and will also support NextGen is Automatic Dependent Surveillance-Broadcast, or ADS-B Out. According to program officials, the system relays the GPS-computed position of the aircraft to the aircraft's transponder and broadcasts it out from the aircraft once a second. This increased rate of position notification is much more accurate than the average 4-5 second sweep-rate of traditional secondary surveillance airport radars.

"(ADS-B Out) allows for more precise reporting of position and information, such as velocity, that can be used in applications other than air traffic control" said Brandt.

For example, aircraft equipped with ADS-B In receivers can receive other aircraft ADS-B Out signals and, through cockpit displays, provide enhanced situational awareness to the pilot. The accuracy of the GPS position also enables improved surface surveillance and conflict-avoidance management at busy airports.

ADS-B Out is mandated to be implemented in U.S. airspace on Jan. 1, 2020, and in Europe June 7, 2020.

In addition to NextGen, Brandt says there are other efforts across the globe under various names, but the philosophy remains the same, replacing the capabilities provided by an extensive, dated network of ground navigation aids with GPS-based technology.

"The use of GPS in civil aviation has grown significantly over the last decade, but there are airlines operating aircraft still today that do not use GPS," he said.

This is largely due to the previous use of selective availability, which was an "intentional degradation of public GPS signals implemented for national security reasons," according to the GPS.gov website. In 2000, President Clinton authorized its discontinuation to ensure all users, whether military or civilian, could receive the most accurate information available.

According to Brandt, the ADS-B mandate will drive more civil aircraft to use GPS, so its importance as critical infrastructure will continue to grow.

The CNS/ATM program was originally stood up by the Secretary of Defense in 1996 to address the addition of Navigation Safety equipment on Air Force aircraft after a couple of high-profile incidents, including a CT-43 crash into a mountain in Croatia that killed then Secretary of Commerce Ron Brown.

Since that time, according to program officials, the CNS/ATM program has become the Center of Excellence for the Air Force for all capabilities related to civil airspace access. Recently the Division has teamed with Air Force Life Cycle Management Center Avionics Engineering Division and the Space and Missile Systems Center GPS User Equipment Office to develop a set of recommendations on courses of action Air Force aircraft can take to integrate ADS-B, Mode 5 IFF and the new M-Code GPS capabilities, which will be presented to the AFLCMC commander during a review in August.