In the first hour of 25 September, two United crews told Los Angeles controllers that satellite navigation had gone bad. UA1962, an A321neo registered N24542, was climbing out of LAX for Chicago when the call came at 00:36 Pacific. UA1866, San Francisco to Dallas at 35,000 feet, reported similar interference at 01:15. Both aeroplanes continued and landed. AIRLIVE also named Alaska AS222, a 737 MAX 9 from San Diego toward Kona, in an offshore sector off the same coast. No official source has said how many other flights felt it, or whether the signal was jammed, spoofed or merely sick in the box. The cause is not public. That is the point. GPS trouble used to be a briefing item for the eastern Mediterranean. It is now a call on a domestic frequency over the busiest Pacific gateway in America.
The same night there was an FAA flight advisory, CHLKCA GPS 26-07: scheduled interference testing centred on China Lake, 20-25 September, 06:01Z to 13:00Z, with possible effects on GPS, WAAS, GBAS and ADS-B that grow with altitude. AeroCorner noted the coincidence and the absence of an official link. Military tests in the California desert are a known source of civil complaints. So are illegal transmitters and sloppy shop gear. Until the FAA or the airlines publish a finding, the test window is context, not a verdict.
Jamming drowns the weak satellite signal so the receiver loses a fix. Spoofing feeds a fake one so the box believes a lie. Crews are told to watch for both and tell the tower. What they fly on next is older than GPS with inertial reference, VOR, DME, ILS, and a controller who still owns the radar picture. A modern airliner is designed to cross an ocean if the constellation goes quiet. It is not designed for a crew that trusts a false position while the map looks calm. That is why the Ruidoso air-ambulance crash in May revealed GPS interference cited among the factors had four dead.
Who owns the picture is unfinished business. Pilots see the flags. ATC sees what the Mode S and ADS-B feeds still claim. The FAA collects reports. Disclosure to the public is slower than the radio call. Oceanic arrivals from Asia that join the LAX stream on RNAV and RNP procedures have more to lose if the same corridor is is missed approach in IMC with a map that cannot be trusted is a different problem from a midnight climb toward Chicago.
The two United sectors ended on a runway. The useful question is how often the same call is now being made on the Pacific slope, whether the published test is the whole explanation, and who tells the next crew before they arm the approach. Satellite navigation made the sky look precise. Interference makes it a cross-check again.