Why doesn't the GPS not work while flying on an aircraft?

APX7000 · Jul 15, 2016

While flying commercial airlines, the GPS doesn't work. Why is this? I'd just like to know where I am and how close to my destination is.

Now here's the weird part. When the pilot says to turn off all electronics and cellular, I go into airplane mode. While waiting to take off in airplane mode, the GPS works great, but once the craft takes off, wham!, the GPS no longer works. Why is this? Do the pilot have the ability to block civilian GPS signals?

I'm using the pricy Garmin GPS app that stores all maps on the iPhone, so no data is ever needed while in airplane mode.

If the aircraft is actively blocking GPS, fine. But it's so odd while taxiing to take off the GPS works great, then wham, it stops working.

Any ideas why?

scifan57 · Jul 15, 2016

I'm amazed that your GPS will work in airplane mode since airplane mode turns off all radios, including the GPS.

As to why it doesn't work in flight, the metal fuselage of the aircraft does a great job of blocking the GPS signals. I've found that if you have a window seat and hold the GPS device or iPhone next to the window, you'll get a usable signal. I used it while flying from Vancouver, British Columbia to Sydney, Australia and it worked perfectly, accurately predicting the flyover of Oahu from 39.000 feet.

APX7000 · Jul 15, 2016

My iPhone had been in airplane mode for 10 minutes waiting for takeoff. I was able to see where I was at the runway.

Yes the GPS is a "radio", it's only a receiver which never transmits a signal.

What's odd is it works while waiting for runway to takeoff, but once the airplane takes off, no GPS signal.

Even in the isle seat, I could always get a GPS signal, but it suddenly stops when the aircraft takes off. This makes me believe they have a GPS blocker on the aircraft. My Garmin apps just says "searching for signal"

scifan57 · Jul 15, 2016

It's highly unlikely that any sort of GPS jamming or blocking technology is used by any airline as the possession and use of such devices is illegal. Passive blocking by the aliminum skin of the aircraft is widely reported and is probably what is causing your problem.

bear7962 · Jul 15, 2016

When Airplane Mode is on, you'll see

in the status bar of your screen or on your watch face. In Airplane Mode, these wireless features are turned off:

Cellular (voice and data)
Wi-Fi
Bluetooth

If you have a device with iOS 8.2 or earlier, Airplane Mode will also turn off GPS.

Assuming you are on a later IOS, I believe your issue after you leave the ground may be inability to lock into a cellular tower to track from.

APX7000 · Jul 16, 2016

Thanks for all the replies.

I've sat in the aircraft for 40+ minutes before takeoff and even in airplane mode I was able so see my exact location. It was only when the flight took off did I stop receiving GPS signals.

All I'd like to know is where I am in the sky's while flying and how close to my destination I am.

bear7962 · Jul 16, 2016

I usually get that in-flight from the airline's wifi but you may be looking for something more precise.

APX7000 · Jul 16, 2016

I fly cheap! Many times my baggage fee costs more than the flight itself.

Id be happy with the inflight GPS data, just the cheap airlines I fly don't even have wifi.

My GPS seems to cut off as the craft just gets ready to get airborne.

tecknomage · Jul 18, 2016

iPhone GPS uses both actual GPS signal and cell signal for these function (your location). While on the ground in an airplane you may receive these signals, when airborne you loose these signals.

Skull One · Jul 19, 2016

Lets look at some realities about GPS in general, a plane on the ground vs a plane in flight and iPhone GPS.

So GPS in general (and yes I know most of you already know this but for the few that don't lets help them out):

There are 31 (some sites say 32 but I don't think the last one has actually launched yet) total GPS satellite currently orbiting the planet.
24 are needed to allow the average device to see 4 at any given second from most points on this planet.
27 are currently being used to give better coverage .
Your device needs to see 3 data streams to get a two dimensional postilion (no altitude).
Your device needs to see 4 data streams to get a three dimensional postilion.
The more data streams, the more accurate your position can become (up to a certain point, say about 9 meters/30 feet).
WAAS based consumer GPS receivers (when used in the US) are even more accurate (say about 3 meters/10 feet).
The data stream from a GPS satellite is at a very slow speed (50 bits per second. Average human can read data sent at 4800 bit/s to 9600 bit/s).

That should cover the basics of the GPS system.

A plane on the ground vs in the air:

On the ground, can see WiFi and cellular towers. With know collected data, can give you a GPS fix in a matter of seconds.
In the air (say 27K feet or higher and traveling at 450 to 650 mph) you won't be able to stay fixed on a WiFi or cellular tower long enough for the data to mean anything.

Where does that leave us? The iPhone has to read the GPS stream from at least three satellites (something it is not very good at) and keep a lock on those streams. Why isn't it very good? Well because the antenna size is too small to collect the very slow and low wattage signal from the GPS satellites. Which is why they use WiFi and cellular towers to get a fix.

So guess what happens if you aren't sitting next to a window on a typical commercial jet? You don't get enough of a signal to get a lock on the stream. Sorry, that's just the way it is. The data stream is simply to low of a power to punch thru the skin of the aircraft and still be viable for the iPhone to receive. BTW even next to a window I would highly recommend you place the phone against the window to get the best chance of locking on to a data stream. But that creates a whole new issue. You just put the phone in a position to only see three satellites. Add into the fact that you need a good 3 minutes worth of steady data from those three GPS satellites to get your initial fix, odds are you aren't going to ever get a lock on your position until you land.

BTW, my rough guess, the antenna in the iPhone would need to be at least the size of the iPhone 6 Plus to be big enough to collect enough of the signal that you could sit more than one seat away from the Window and still get a fix. Either that or the will have to start making planes that don't use so much metal for the outer skin.