As reported by Forbes: "Does anyone know what happened to GPS/ADS-B last night?" one aviation commentator asked Twitter on June 9, a Sunday. "The issue seemed to be quite wide-spread, with a lot of aircraft grounded... Had this happened on a weekday, it would have been leading headlines on national news—some sort of GPS fault grounded a chunk of the U.S. commercial fleet and hardly anybody noticed."
But at the time of publishing that issue remains unresolved and the weekend is all but over.
According to the FAA, "certain aircraft equipped with the Rockwell Collins GPS 4000-100 and select ADS-B out GPS receivers are indicating 'ADS-B fail, unavailable, TCAS fail or transponder fail' messages." Aircraft without working transponders were directed to coordinate with the FAA before departure, a prior directive had instructed those planes not to fly above 28,000 feet.
Rockwell Collins, acquired by United Technologies last year, provides avionics and information technology systems and services. The issue appears to center on some of the company's ADS-B (Automatic Dependent Surveillance-Broadcast) systems that send flight data to be picked up by ground stations. "The ADS-B system depends on GPS data to function properly," explained Hackaday, "but a problem with the quality of the GPS data has disrupted normal ADS-B features on some planes."
Whether the issue was caused by poor GPS data or a software upgrade to affected systems remains speculation, nothing has yet been confirmed. But, whatever the cause, the issue has led to a significant number of flight cancellations. According to CNBC, regional carriers in the U.S. "canceled about 400 flights scheduled for Sunday." A Delta spokeswoman said "about 80 of its regional flights were canceled," and American and United regional carriers were hit by the same issue.
Various online reports suggested impacted planes were mostly CRJ jets made by Canada’s Bombardier, but also some Boeing 737s, 717s and possibly a 767 as well. "We are working to determine the cause of the problem," the FAA said in a statement, "which may have resulted from a software update to the aircraft navigation systems."
A Collins Aerospace spokesperson told me by email that "we identified a technical issue with our recently released GPS product(s) impacting availability, and have since determined the root cause and the resolution. We are engaging with our customers to ensure continued safe operational capability."
"GPS isn’t down," Hackaday reported, as anyone with a smartphone can see easily enough. "However, it is degraded. How a plane’s GPS system reacts to that depends on the software built into the GPS receiver. If the system fails, the pilots will have to rely on older systems like VOR to navigate. But ADS-B will have even more problems. An aircraft ADS-B system needs position data to operate. If you can’t transmit your position information, air traffic controllers need to rely on old fashioned radar to determine position. All of this adds up to a flight safety problem, which means grounding the aircraft."
There has been online speculation that military testing of GPS jamming might be responsible, although that seems to have been discounted—such tests are heavily publicized beforehand. There was also apparent confusion for some airline passengers, with disruption being blamed on the weather rather than on system issues. "Hey Delta," one passenger tweeted, "some updates would be nice. Y’all keep saying weather but our pilot just said the military is jamming Delta’s GPS which is why we were diverted."
What is clear, is that the issue is more widespread than its lack of publicity might suggest. This comes just as extensions have been announced to the grounding of Boeing 737 Max aircraft following accidents that killed 346 people, as well as speculation around aircraft drone safety measures. And so the quality and reliability of aircraft flight support and navigation tools have been very much headline news.
At the time of writing, the situation is evolving, and we will soon find out if this weekend issue is set to cause Monday morning travel chaos.
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