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In a recently released paper, the respected analytics firm London Economics determined that the presence of backup systems at the Denver and Dallas Fort Worth airports prevented any noticeable impacts on air travel despite each having experienced a disruption of GPS signals for 24 hours or more. By contrast, recent GPS interference at an airport without a backup system caused scheduled air service to be canceled until an alternative to GPS was established.

Also important to the lack of impact at Denver and Dallas was that the signals interfering with GPS, with a few minor exceptions, only impacted aircraft in the air.

GPS is essential for the safe and efficient movement of aircraft and support vehicles on the ground at airports, as well as the transport of crews, passengers, supplies, and cargo to and from airports, communication systems, and numerous other services.

Backups needed for both air and ground

Previous work by London Economics has shown that disruption of GPS for these ground functions would likely cause numerous flight delays and cancellations. Delays in the arrival of flight crews, passengers and supplies, for example, would quickly upset flight schedules. If this happened at a major airport, such as Denver or Dallas Fort Worth, disruptions could ripple through the entire air transport system. Wide-spread delays, cancellations and schedule adjustments would bog down air travel across the nation, if not the world.

The incident in Denver was caused by an accidental transmission from a government installation on Jan. 21. 2022. It impacted aircraft within approximately 50 nautical miles of the airport and lasted 33 hours before the source was identified and turned off.

The Dallas incident began on Oct. 17, 2022, and affected aircraft within about 110 nautical miles. It continued for 24 hours before ending on its own. The source has never been identified.

Reducing aviation backups may be a bad idea

In addition to recognizing the value of terrestrial navigation systems for aviation, the London Economics paper cautions about moves in the United States and Europe to “rationalize” these systems by reducing their number. In the event of longer or widespread GPS disruptions, the impact of an insufficient number of terrestrial systems could be significant. The cancellation of air service to an airport in Estonia because of chronic GPS jamming is used in the paper as a cautionary tale.

Instead of reducing the number of old backup systems, London Economics suggests policymakers consider establishing more widely available sources of terrestrial PNT. Taking a fresh look might identify alternative PNT sources for aviation that could also be used by other critical infrastructures. Perhaps even in consumer applications as well.

U.S. government representatives were approached for consultation and comment for this paper and expressed their willingness to participate. Unfortunately, they were unable to obtain permission to do so.

London Economics’ work on this effort was commissioned by the Resilient Navigation and Timing Foundation.

The paper “Aviation GPS Incidents Show Importance of Backup Systems. Policy Makers Take Note.” can be accessed from the foundation’s online library here.