Ask Different is a question and answer site for power users of Apple hardware and software. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I have a very basic question: if I enable GPS in my iPhone when in an airplane cruising at an altitude between 30000-40000 feet (roughly 9-12 km), will the GPS actually give valid data?

I read a couple of articles (linked below) but I'm still confused whether GPS will work or not.

  1. https://www.quora.com/Does-mobile-GPS-work-onboard-airplanes
  2. http://aviation.stackexchange.com/questions/8188/airplane-mode-does-not-disable-gps-is-it-safe-to-use-gps-in-flight

Thanks

share|improve this question

For most practical situations, GPS will work well enough for you to track your progress but not have great coverage (less than 2m accuracy) or accurate speed over ground readings from iOS.

From an antenna / physics perspective, you may have horrendous GPS reception since you are riding inside a mostly complete faraday cage. Even if you have your phone in a window, all the visible satellites might be in a configuration where GPS is very poor or unable to generate a usable fix.

Clearly, cruising altitude is generally one of the best places for GPS reception as long as the antenna is placed on a tip / extremity of the plane. You don't have multi path interference to speak of, no foliage, and no hills or buildings to interfere with a clear view horizon to horizon - not to mention that your altitude will let you see more than the normal "half the sky" visibility you get on the ground at best.

The phone hardware and iOS will certainly try to get you the best fix it can once you have the device out of Airplane mode. I know many pilots that report the iOS GPS in the cockpit is quite good / on par with the other consumer and even commercial navigation products.

share|improve this answer
1  
I don't have an iphone, but my samsung phone's gps is very reliable while at cruising altitude (at least on a window seat, which I mostly use). I have tried this in many different flights, and the numbers shown by the phone's gps always agree with the plane's displayed data and map. – Martin Argerami Jan 29 at 18:38
1  
@MartinArgerami I agree - when you would get 2m to 10m accuracy of a fix with iPhone, you might get 10x the error, but if you are off by half a mile or more, does it really matter while you are tracking your flight? In practice, mobile GPS chipsets works just fine in any aircraft where humans are without pressure suits and even in many military aircraft. – bmike Jan 29 at 18:43
1  
Is the airplane really much of a faraday cage? My phone gets good enough reception on the ground that I can stream movies, which seems to me like the signals are getting in/out just fine. – Cornstalks Jan 30 at 16:52
1  
@Cornstalks the GPS signal is very much weaker than your 3G/4G/wifi signal... – Thruston Jan 30 at 18:25

Domestic Satellite Navigation systems usually include limitations as a security measure. The general rule is that nothing off the shelf should be able to assist in the creation of a guided missile.

To that end most, if not all, civilian GPS units will fail or work poorly if any of the following conditions are met:

  • High Altitude - Once you are higher than a mountain you are no longer a normal civilian user. This limit is usually very high though, more commonly edge of space rather than domestic airline altitudes.
  • High Speed - If you are doing more than one or two hundred miles an hour you are probably a high speed vehicle or missile. That being said the limit could be set close to the speed of sound so that civilian aircraft are unlikely to hit it.
  • High Dynamics - If you are performing high speed turns you might be a missile or air-craft evading attack. It is usually not possible for commercial passenger aircraft to perform manoeuvres that trigger these limits though.

You may find that this causes an issue when using your phone on-board an aircraft. I use to build test equipment for GNSS systems and would often find GPS units behaving strangely if I started to simulate any of the above conditions.

Poor reception due to the fuselage is also a possibility. To test if this is the limiting factor, rather than the security measures, simply try using your phone's GPS within the plane while it is on the ground before take-off. If you can get a position fix before take-off but struggle once in flight it will be the security measures limiting you. I would expect most phones to not be limited by this though. If you can use it inside a bus or train without being by a window I would expect the shielding and signal levels to be similar to inside a aeroplane.

share|improve this answer
    
How would a GPS system technically prevent a fast-moving or fast accelerating receiver from working? GPS is (or can be used) entirely passively; the sender has no way of knowing who receives it, and under which conditions. Do you have references? – Peter A. Schneider Jan 29 at 13:01
1  
@PeterA.Schneider is referring to CoCom regulations for hardware manufacturing. en.wikipedia.org/wiki/CoCom – Stephen P. Jan 29 at 13:51
2  
Even more so than security measures, GPS receivers intended for typical civilian use are designed with that use case in mind. Their signal processing is configured such that it will provide good performance (i.e. high tracking accuracy) in typical user scenarios (moving at car speeds or less, on the ground). High dynamics, altitude, or speed can all result in poor performance, even if not by specific security-based design, by nature of the receiver processes that are tuned for "normal" conditions. – Jason R Jan 29 at 13:54
    
@StephenP. I see; the limitation is in the receiver. Wikipedia reports the limits as 1900 km/h and 18,000 meters though, both beyond current civil aeronautics. Since CoCom (-successors) concern exports out of the US, GPS receivers elsewhere are not impacted, cf en.wikipedia.org/wiki/… – Peter A. Schneider Jan 29 at 14:32
1  
@LovesTha Just to reiterate: A passenger plane does noot meet either of the criteria for the ITAR restrictions to kick in (too [s]low), and some of the answers here contain first-hand accounts of off-the shelf GPS devices, including apple products, working in-flight. (Others provide first-hand accounts of them not working, sure; that can have all sorts of reasons, but ITAR is not one of them.) – Peter A. Schneider Jan 30 at 9:18

This is from a fact, on my last trip, I was trying to see how fast the airplane was travelling using Speedometer app on iPhone 5c. It didn't work.

Speedometer doesn't show location, so I tried Strava. It also didn't show speed, but it's showing that the position on map jumped occasionally.

I don't think it's GPS signal issue, I brought a Garmin bike computer one time and it recorded the flight just fine. I still have the records of a couple of flights, it's interesting to see that planes don't just take the shortest path. The only thing that didn't look right was the altitude, since it's using barometer and the cabin is pressurised.

share|improve this answer
2  
It's interesting that it got the altitude wrong. GPS is a 3D system (actually 4D, as it solves for time offset as well), and normally the height would be calculated from the GPS loci. But if the receiver can only "see" 3 satellites "good" software will guess the height - I'm guessing that's what Garmin did. The down-side of that is that guessing wrong (as it did) will introduce positional errors... – Grimxn Jan 29 at 8:48
    
@Grimxn: Many GPS devices also have a pressure-based altimeter. It's sometimes a selectable setting whether the altitude readout is based on that or the GPS data. I believe the altimeter is better at detecting small altitude changes. – Nate Eldredge Jan 30 at 16:34
    
@NateEldredge: It will indeed be - but my point was that if a receiver can see four or more satellites, it will at least be able to estimate height as well as time offset and 2D horizontal position, but if it could only see three satellites (quite likely inside an aircraft), it would use the altimeter (wrongly, in this case) to constrain the Z in the solution... – Grimxn Jan 30 at 18:05
    
I just look at the record again and I think less accurate is more correct, since the cabin pressure is more constant. There were small dips after the planes landed. – imel96 Jan 31 at 18:01

It will work, but you must hold the phone at the window. And sometimes it takes plenty of time to fix the signal.

share|improve this answer

I can't speak to an iPhone specifically, but an iPad Air 2 works just fine as long as I'm in a window seat. I use ForeFlight, software used for navigating while flying, all the time during commercial flights when a passenger. During the climb/descent a turn might throw it off and it'll take a few seconds to reacquire the signal, and it might require holding it right to the window to reacquire position. But in cruise, once it's got a position, I can leave it on the tray table and it'll happily show position, ground speed, and GPS-computed altitude for a half hour or more without issues. The altitude is of course slightly off because when you're in cruise the plane is flying not at a fixed "feet" altitude but rather at a given flight level.

share|improve this answer

GPS itself works very well even in space. As the other answers have already mentioned the problem with low signal inside the plane is probably the biggest problem you will face.

However, all GPS receivers are limited to speeds and altitudes.

See http://gizmodo.com/5824905/your-gps-doesnt-work-at-mach-2-because-its-afraid-youre-a-soviet-spy

share|improve this answer
1  
The fear is not that you are a spy, but a high speed nuclear missile. – gnasher729 Jan 29 at 17:09

Here is a picture that I have taken in the plane using my iPhone 6. It is the IGO application on the screen. I do not know the exact altitude but it was really high. You can see our ground speed.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.