The US military has been conducting large scale national security exercises in which GPS navigation signals are degraded to test defense systems and preparedness. I certainly understand the necessity for such testing – I want us to be ready for anything the bad guys throw our way, but has the FAA done enough to educate and inform the pilots flying into and out of the airports and airspace affected by these tests?
The number of jamming events and their locations are increasing and the tests have resulted in a growing number of pilot complaints, as well as less than ideal aircraft performance and handling characteristics. As the proliferation of satellite-based navigation continues, the problem of GPS interference is expected to multiply.
GPS navigation may be unreliable or unavailable in a large portion of airspace while the military is jamming the GPS signals. During the test period, GPS based services, including Automatic Dependent Surveillance-Broadcast (ADS-B), the Ground Based Augmentation System and the Wide Area Augmentation System could also be lost in a radius of several hundred miles from the operations center.
The FAA will post a flight advisory that gives the schedule of the current round of tests and NOTAMs will also be issued for the airspace, but I think broader pilot training and education is necessary. For instance, during tests in November 2018, AOPA reported several instances of aircraft veering off course because of the loss of GPS signals (https://www.aopa.org/news-and-media/all-news/2018/november/28/less-isnt-more-for-gps-and-flight-safety). There have also been documented cases of ATC temporarily losing the tracks of ADS-B Out equipped aircraft.
Specific examples of the safety hazards involving civil aviation navigation and aircraft control, have been reported and collected by the FAA, including a business jet that entered a dutch roll and emergency descent when its yaw damper disengaged on its own: the dual attitude and heading reference system had reacted differently to the GPS signal outage. This issue was specific to the aircraft and has been corrected, but there are hundreds of other reports of aircraft departing under IFR and losing GPS on initial climb out and others losing GPS navigation capability and not regaining it until after landing.
Military testing will continue and it is up to us, the pilots, to be aware of when and where the next test will be occurring. Always check the NOTAM’s for your route of flight and read any flight advisories posted by the FAA. Continued pilot training and application of that knowledge will help keep you in-the-know.