A warning has been issued to pilots by the Federal Aviation Administration that on June 7, 9, 21, 23, 28 and 30, they’ll be conducting GPS interference testing between 9:30 a.m. and 3:30 p.m. PST. People on the ground probably won’t notice the interference, but it will affect aircraft 50 feet or higher (up to 40,000 feet).

As MNN's Bryan Nelson described in more detail, the testing is centered around China Lake, California, in the Mojave Desert. That’s where the U.S. Navy’s Naval Air Weapons Center is located. It affects a large area, overall, which you can see below.

the map distributed by the FAA that details the GPS outages on the days concerned. This is the map distributed by the FAA that details the GPS outages on the days concerned. (Photo: FAA)

Embraer Phenom 300 business jets are being advised by the FAA to avoid the area completely as the outage could affect their flight stability controls, but no other advisories are made for other types of planes. Which begs the question: What does a pilot do if he is mid-flight and the GPS goes out?

The good news for all us nervous flyers is that while GPS may be convenient for pilots, it's not necessary to fly most planes. GPS serves to help cut route distances more easily, and leaves room for a pilot to do other things, whereas navigation used to be a more involved part of the job — but it's not unsafe to fly a plane sans GPS. After all, GPS didn't even exist until 1994, and there were thousands of flights a day departing and landing safely by then.

As pilot Bob Watson writes on Quora, "With the GPS keeping its finger on the map and computing the ETA, I can concentrate on things it's not doing like looking out the window for traffic, keeping an eye on the engine temps and fuel consumption, plan the next step of the flight, etc. So, I still have a sense of what's going on around me."

Of course, pilots of large jets and small planes navigated just fine before GPS became widely available. In fact, part of a pilot's training (some say the hardest part) is learning various ways to navigate. Private pilot Paul Mulwitz writes, "In flight the plan is checked against actual progress at planned check points. Other well established methods of aircraft navigation include pilotage where the features on the ground are compared to shapes and other features on aviation charts and several different versions of radio navigation that use receivers in the aircraft to locate the aircraft in flight or to help it fly toward its desired destination."

Here's an explanation of how pilots navigate an airplane:

Navigating over open ocean is a bit trickier when GPS is down, but it's still possible. And the FAA GPS interruption won't be over open ocean.

What’s the reason for the test? Well, the Navy isn’t telling. “I can’t go into the details of the testing, it’s general testing for our ranges.” Deidre Patin, a public affairs specialist told Gizmodo. But there are some educated guesses: A good guess would be that the Navy is concerned about the ability of cheap jamming software (available now that the technology is so common) interrupting military or civilian operations. Another supposition is that the military wants to figure out how to prevent drone terrorism.

Either way, don't worry if you're flying on any of these days. Says pilot Doug Hanchard: "A 10-year-old can fly an airplane without GPS. GPS is not mandatory and nor is it 'difficult'."

Starre Vartan ( @ecochickie ) covers conscious consumption, health and science as she travels the world exploring new cultures and ideas.