United Flight Five Twenty-Eight, the Maui GPS Jamming Incident, and What Happens Inside the Cockpit When the Navigation Picture Goes Dark

United Airlines Flight 528, operating between the U.S. mainland and Maui, reported significant GPS anomalies during approach to Kahului Airport. The flight management computers flagged navigation integrity alerts, and the crew’s GPS-derived position was unreliable during one of the most GPS-dependent approach environments in U.S. commercial aviation. The crew cross-checked, reverted to conventional navaids, and landed without incident - but the report filed afterward joined a growing stack of similar events the FAA and aviation safety community are now working to understand.

What Happened on United Flight 528

Kahului Airport sits in terrain that leaves little room for navigational ambiguity. The airport relies heavily on RNAV procedures, which assume GPS is healthy. When the flight management system began flagging integrity alerts, the crew faced exactly the transition that GPS dependency makes harder: moving quickly from a GPS-centered mental model to ground-based navigation.

The handling was professional and by the book. Cross-check, revert, land. But the significance of this event is not what happened on that flight - it is what that flight represents in a pattern of interference reports accumulating across the Pacific region and parts of Southern California.

GPS Jamming vs. GPS Spoofing: What’s the Difference

Two distinct failure modes are relevant here, and they are not equally dangerous.

Jamming is the broadcasting of radio frequency noise on or near the GPS frequencies - 1575.42 MHz for the L1 signal and 1227.6 MHz for the L2 signal - strong enough to overwhelm the satellite signal. The receiver loses lock and tells you it has no position. This is the better failure mode. You know something is wrong.

Spoofing is more insidious. A spoofer broadcasts a false GPS signal that mimics the real satellites but contains deliberately incorrect position data. The receiver accepts it because it looks legitimate. The display shows a position - just the wrong one. A pilot may not recognize the error until cross-checking against a VOR, DME, ILS, or visual landmark. Reports from the Maui area and parts of the Los Angeles region suggest a mix of both phenomena, though definitively attributing the source of any GPS interference event is technically difficult and investigations are ongoing.

Who Is Causing GPS Interference Over the Pacific

Military electronic warfare exercises are a known, legal source of GPS interference, and the Western United States and Pacific region carry a dense schedule of such activity. The Pacific Missile Range Facility at Barking Sands on Kauai, the Channel Islands off Southern California, and ranges over the Nevada desert are all active users of electronic warfare spectrum. The FAA publishes NOTAMs when military GPS testing is scheduled. Some interference pilots are reporting is likely bleed-over from those exercises.

There is also geopolitical context that aviation security researchers are actively examining. GPS spoofing has been documented in conflict zones and near actors with sophisticated electronic warfare capabilities - the Black Sea, Eastern Mediterranean, parts of the Middle East, and the Korean peninsula have all seen spoofing events not attributable to friendly military operations. Whether some of what is occurring over the Pacific has a different origin is an open question in defense and aviation security research circles.

Why Modern Aviation Is So Vulnerable

The Global Positioning System is a constellation of roughly 31 operational satellites in medium Earth orbit, maintained by the United States Space Force. Each broadcasts a precise timing signal; a receiver listening to at least four simultaneously can determine position to within a few meters. The system is extraordinary when it works. The problem is how deeply it is now embedded in aviation at every level.

Modern flight management systems on aircraft like the Boeing 737 MAX and Airbus A320 family are built around GPS for both lateral and vertical navigation - RNAV departures, RNAV arrivals, Required Navigation Performance approaches demanding accuracy to within less than a tenth of a nautical mile. The automation assumes GPS is healthy. When that assumption breaks, crews must transition quickly to a different positional picture.

General aviation is in some ways more exposed. Many GA pilots fly routes and approaches where GPS is not just the primary system - it is the only system. No VOR, no NDB, no ILS. Just RNAV. And across both professional and GA environments, the reliability of GPS over the past two decades has allowed non-GPS navigation skills to quietly atrophy. Not through negligence - through the natural human tendency to lean on the tool that works 99 percent of the time.

The VOR Minimum Operational Network and Why It Matters Now

The FAA has been navigating a slow, contested debate over the VOR Minimum Operational Network (MON) - the agency’s plan to maintain a reduced backbone of VOR stations as a GPS fallback. The goal: any IFR pilot in the contiguous United States should be able to navigate to an airport with an instrument approach using only VOR and DME within 100 nautical miles, even with GPS fully unavailable.

The MON has faced delays, budget pressure, and skepticism from those who argue GPS is reliable enough that a fallback network is unnecessary overhead. Events like the Maui reports are the direct counter-argument.

Most modern airliners also carry inertial reference systems (IRS) - units using accelerometers and gyroscopes to track position changes from a known starting point, independent of GPS. They drift over time and are normally blended with GPS to stay accurate, but in a GPS-denied environment a well-initialized IRS provides usable position for a meaningful period. Most general aviation aircraft do not carry IRS, which further increases GA exposure in interference scenarios.

What Pilots Should Do When the GPS Picture Goes Dark

Know the frequencies before you need them. Every flight should have VOR frequencies not just in the flight plan as a backup, but actually tuned, Morse code identified, and cross-checked against the GPS. If the moving map lies to you, you want a needle you already know is alive.

Know your approach options at your destination. Before departing for any airport, confirm whether a conventional approach exists - an ILS, VOR approach, or localizer. If GPS is the only approach available and you receive a navigation integrity alert, that is information you need before the final approach fix, not after it.

Brief the anomaly. On Pacific routes and through known interference zones, spend thirty seconds before departure thinking through what you would do if GPS position became unreliable. Pilots who have pre-thought a scenario make better decisions when it occurs, because recognition is already half the response.

File the ASRS report. The Aviation Safety Reporting System, operated by NASA, is the anonymous, penalty-protected mechanism for getting anomaly data into the system. The data researchers and the FAA use to build an accurate picture of interference patterns comes from pilot reports. Flight 528’s crew filed. More should.

The Maui GPS interference events are not a catastrophe. No one was hurt, and the crews involved responded correctly. But they are a signal: the system most trusted is the one most worth understanding completely, including its failure modes.

Sources: AVweb, AOPA Pilot, FAA NOTAM and ASRS databases.

Key Takeaways

United Flight 528 reported GPS navigation integrity failures on approach to Kahului Airport, Maui, consistent with a pattern of GPS interference events accumulating across the Pacific and Southern California regions.
GPS failures take two forms: jamming (receiver loses lock, obvious failure) and spoofing (receiver accepts false position data, potentially invisible without cross-checking).
Military electronic warfare exercises at facilities including the Pacific Missile Range Facility at Barking Sands, Kauai are a documented source of interference; other origins remain under investigation.
The FAA’s VOR Minimum Operational Network exists precisely as a fallback for GPS-denied scenarios, and its case grows stronger with each documented interference event.
Every pilot - professional or GA - should brief GPS anomaly procedures before flying GPS-dependent routes, maintain cross-check discipline with conventional navaids, and file ASRS reports when interference is encountered.