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'Buzzer' beater

Flight planning in the age of GPS jamming

June is packed with flight advisories about scheduled GPS outages in some parts of the country, a reminder to general aviation pilots that no digital-age flight planning session is complete without checking for GPS “interference events.” And more GPS jamming lies ahead.

Photo by Chris Rose.

As the air traffic system migrates from the legacy navaid network to GPS, defense technology is on a similar path. The transition has created the need to train personnel and test equipment in what officials call a “denied environment”—one where GPS reception is intentionally reduced.

The military and the FAA coordinate GPS-signal degradation scheduling, with the FAA disseminating flight advisories such as this one that informed pilots of interference testing at New Mexico’s White Sands Missile Range on numerous days in June with GPS navigation possibly unavailable in a varying radius of hundreds of miles at altitudes from 50 feet agl to the flight levels. The outage included expected loss of Automatic Dependent Surveillance-Broadcast (ADS-B) and Wide Area Augmentation System (WAAS) capabilities.

For GA, lost or degraded GPS navigation has not been the only complication of interference testing. In a filing with the Aviation Safety Reporting System, a business jet captain who had been alerted to possible signal loss by air traffic control described how uncertainty and distractions led to multiple deviations during descent toward the terminal environment, adding, “I think it was because my first officer and I were discussing how confusing all the changes were and how the GPS outage was going to affect our arrival.”

As denied-environment activities have increased in scope and frequency in recent years, AOPA has been critical of the FAA’s response to the need to pay more attention to the safety implications of GPS jamming and has advocated for the agency to act on recommendations issued in 2018 by an AOPA-co-chaired working group of the technical guidance organization RTCA.

As a stopgap measure, AOPA is advising pilots that when an in-flight loss of GPS reception degrades flight safety, the pilot in command should notify ATC to “Stop buzzer,” a phrase used to immediately halt a GPS interference activity. (A pilot invoking “Stop buzzer” should first ascertain that it is the GPS signal, not on-board equipment, that has faltered, even though this takes time and taxes pilot workload.)

That possibility has officials’ attention. Interrupting a denied-environment training exercise or systems test can be a seriously costly disruption, and the military is working internally and with the FAA to find ways to “deconflict” GPS interference events as much as possible, said Edward J. Chupein, deputy chief of the U.S. Air Force Operational Training and Infrastructure Division.

In a June 11 interview, he noted that the number of those events had increased from about 41 in 2012 to 128 in 2017, and “will continue to increase.” Within the Defense Department, mitigating the impact of GPS interference on nonparticipating aircraft starts with “a better way to communicate amongst ourselves,” especially to head off the most troublesome kinds of events—those that overlap between the military branches, or between testing and training. A related goal is to prioritize GPS interference activities, he said.

Chupein noted that officials are exploring ways to work with the FAA to minimize the impact of interference events by taking into consideration factors beyond how the FAA’s Air Route Traffic Control Centers color-code time period traffic volumes as red, yellow, or green for GPS interference, because sometimes those planning boundaries are not workable. He named alternative proposals, including evaluating the density and complexity of air traffic or managing the direction in which GPS is jammed.

Some solutions could be one-offs: In an example of what he termed “dynamic mitigation,” he said a pilot might report signal degradation that could be passed along “to the source of the jamming,” where adjustments could be made, restoring signal integrity, followed by a decision to “resume, or continue with that mitigation.” (An aircraft’s installed equipment, even the placement of its antenna, can have a significant effect on GPS reception, but the Defense Department takes no position on GA equipage, he said.)

Pilots’ preflight awareness of GPS interference remains an important remedy for conflicts. Chupein noted that the FAA’s notice to airmen (notam) system can be “kind of overwhelming” as a source of information about what is going on, and where, in the airspace system. Discussions between the government agencies have focused on finding ways to narrow the effects of GPS interference events and pinpoint the effective times of event notams to make the information more useful.

One promising area of research is focused on technological solutions that would minimize the use of GPS jamming. Not quite “simulation,” but perhaps better described as a way to introduce the needed jamming effects from external sources. “But at the moment no such capability exists,” he said.

Chupein said defense officials recognize that the GPS system “has become integral to our lives,” and when disrupted for national security purposes, “does impose some burden.”

But the need for such disruption “is only going to increase.” As it does, the challenge will be to strike a balance that allows constructive training to take place and bring on line real-time methods to minimize the impact on other flight operations, he said.

In collaboration with airlines that share concerns about GPS interference, AOPA has been meeting with the FAA’s air traffic safety office to find a path forward on further mitigations when jamming is occurring. “We have had some positive conversations in the last month” that have “led to the FAA committing to action on several of industry’s recommendations, but we need to see the results because interference is a daily activity and more effort is needed on the FAA’s part,” said Rune Duke, AOPA senior director of airspace, air traffic, and aviation security. “Initial steps by the FAA include further safety assessments of this activity, controller training, and notam modernization.”

“We constantly hear concerns from general aviation pilots about GPS interference activity and the implications it has for safety and flight efficiency. We appreciate that the military and FAA understand those concerns and are working with us to find a long-term solution,” he added.

Dan Namowitz

Dan Namowitz

Dan Namowitz has been writing for AOPA in a variety of capacities since 1991. He has been a flight instructor since 1990 and is a 35-year AOPA member.
Topics: Advocacy, Airspace, FAA Information and Services

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