Can an airplane land without a GPS?

Military tests endanger passenger jets

The Global Positioning System GPS has been developed by the American military since the 1970s. With the help of this satellite system, it can better locate the positions of its ships, aircraft, vehicles and troops. Nowadays almost every smartphone has a GPS function to use navigation apps and to locate the cell phone.

And airline pilots also use GPS data to navigate their planes. At the same time, however, the military has not stopped looking at the system. The American military, for example, deliberately and regularly interferes with GPS signals. So it can test how its own troops act without correct GPS data. It can also develop and test its own interference systems and interference defense systems.

21 incidents in just one day

This also has consequences for GPS navigation in civil aviation - and to a much greater extent than previously assumed, as the magazine IEEE Spectrum reports. According to this, only around 90 cases have been known in the US from the past eight years, about which pilots reported in NASA's Aviation Safety Reporting System, most of them in 2019 and 2020.

Now, however, the magazine was able to view data from the aviation authority FAA, which documented hundreds of GPS malfunctions in civil air traffic in the vicinity of military tests for a few months in 2017 and 2018 alone. On a single day in March 2018, there were 21 incidents near Los Angeles - a rescue helicopter, several private jets and around a dozen passenger planes were affected.

GPS data manipulated

Each of these incidents is potentially dangerous. One case described in NASA's reporting system revolves around a flight in the state of Idaho in August 2018. In foggy conditions, the aircraft's GPS was disrupted without the cockpit crew noticing. The air traffic controllers reported that only their tip to the pilots at the last minute prevented the machine from crashing into a mountain.

According to the magazine, the military interference can lead to a complete failure of the GPS signal. On the other hand, it is also possible - and usually much more dangerous - that the data can be manipulated. There are reports from pilots who at some point noticed that the autopilot was steering their aircraft on a completely different course due to changed GPS data, sometimes dangerously close to other pilots.

Alerts for huge areas

To prevent all of this, there are warnings. The military published so-called Notices to Airmen, or Notam for short, to warn pilots and air traffic controllers about the tests. The problem: These warnings sometimes cover huge areas, such as the state of Texas or the entire southwest of the USA. This does not mean that disruption will actually occur in the entire area, but that it is possible. Most pilots do not experience anything there despite the warning - and may become dull over time when it comes to the danger.