GPS Team Tracker — FAQ & Knowledge Base
Why no GPS signal is received when you are inside an aircraft
Enabling airplane mode does not disable the GPS receiver, and GPS is technically capable of tracking an airliner at its cruise speed and altitude. However, in practice a phone lying on a tray table inside a commercial aircraft rarely gets a usable GPS fix. The reason is not the phone and not the aircraft's speed — it is the aircraft itself. A pressurised metal fuselage behaves as a Faraday cage, and the extremely weak GPS signal from 20,200 km away cannot punch through the skin of the plane. The only reliable window into the sky is the literal window seat.
Xopoz will continue to run, the map will remain open, and the last-known position will stay displayed — but no fresh position updates will arrive until the GPS chip can see enough satellites again, typically only when you hold the phone close to the cabin window or after landing.
Yes. A typical commercial airliner cruises at approximately 900–920 km/h (around 250 m/s) at an altitude of 10,000–12,000 metres. These numbers are comfortably inside the operating envelope of any modern GNSS receiver.
There is a historical export-control ceiling known as the CoCom limits, inherited from the Cold War, which requires commercial GPS chips to stop tracking when the receiver simultaneously exceeds 515 m/s (~1,852 km/h) and 18,000 metres (~59,000 ft). These limits were set to prevent civilian GPS from being used to guide intercontinental ballistic missiles. A cruising airliner is well under both thresholds — roughly half the speed limit and two-thirds of the altitude limit — so CoCom does not come into play on normal passenger flights.
| Parameter | Typical Airliner (Cruise) | CoCom Ceiling | Headroom |
|---|---|---|---|
| Ground speed | ~250 m/s (900 km/h) | 515 m/s (1,852 km/h) | ~52% |
| Altitude | ~11,000 m (36,000 ft) | 18,000 m (59,000 ft) | ~39% |
Note that some chipset vendors disable tracking when either limit is reached, others only when both are exceeded. Either way, a civilian airliner does not trigger the shut-off.
So if the receiver works fine physically, and airplane mode does not switch the GPS chip off, why does the little blue dot on the map refuse to move?
GPS signals are astonishingly weak by the time they arrive at the Earth. A navigation satellite in medium Earth orbit (≈20,200 km altitude) transmits with only about 27 W of RF power. By the time that signal has travelled through 20,000 km of vacuum and another several kilometres of atmosphere, the power arriving at your phone's antenna is on the order of −130 dBm. Airbus's own safety bulletin puts it memorably: "the GPS signal is comparable to the power emitted by a 60 W light-bulb located more than 20,000 km away from the surface of the Earth" [1].
At 1.575 GHz (the GPS L1 frequency), radio waves propagate in essentially straight lines. They do not bend meaningfully around obstacles, and any conductive material in the path acts as a barrier. A commercial airliner's aluminium fuselage is a near-perfect conductor, forming an enclosed metal shell — the textbook definition of a Faraday cage. Inside such a shell, the incident electric field from the satellites is very largely cancelled by induced surface currents in the skin, and what reaches the passenger's phone is a tiny fraction of what is hitting the hull outside.
Published measurements of RF propagation through commercial aircraft fuselages show that fuselage attenuation is not uniform: it is a directional property. IEEE studies of in-cabin to ground cellular interference found that nose-on and tail-on attenuation can exceed the average fuselage attenuation by more than 30 dB [2]. At L-band (roughly where GPS operates), this translates into a signal that is already a thousand times weaker after entering through the skin, in a link budget where the starting margin was less than 10 dB.
The dominant leakage path for RF inside the cabin is not the metal skin but the cabin windows. This is why systems located in the passenger area experience less attenuation than those in enclosed compartments — the windows are the "holes" in the Faraday cage.
This single physical fact explains the universal hobbyist observation: a phone pressed against a cabin window has a fighting chance of acquiring GPS, whereas a phone on a centre-seat tray table almost never does. Pilots and enthusiasts who have tried this consistently report that a window-seat tablet gets a usable fix around 85–90% of the time, dropping to 40% or less further inside the cabin [3]. The degrees-of-sky-visibility that matter are set not by the plane's altitude but by the size of a 30 × 23 cm oval of acrylic next to your seat.
Worse, the window itself is not always transparent at GPS frequencies. Modern cabin windows often contain a thin conductive coating for heating or dimming (Boeing 787 electrochromic windows, for example), and cabin dust/oil films and the rounded thick acrylic introduce additional loss. On some aircraft you can feel the difference by simply sliding from one row to the next.
Aluminium fuselages are bad; carbon-fibre fuselages are often worse for GPS reception. The Boeing 787 and Airbus A350 are built largely of carbon-fibre reinforced polymer (CFRP), which is a reasonable conductor but also an excellent RF absorber — it tends to soak up radio waves rather than reflect them cleanly. Published measurements on CFRP panels show attenuation on the order of 16 dB per millimetre of laminate in the 2–18 GHz range [4], and typical fuselage skins are several millimetres thick. This is why drone and model-aircraft builders who use CFRP airframes have to route GPS antennas outside the composite shell: inside, the signal is simply gone.
The aircraft itself has no trouble with GPS. Every modern airliner continuously computes its position from GNSS as part of its flight management system, feeds it into ADS-B broadcasts, and uses it for precision approaches (RNP, RNAV) and for satellite-based landing systems. It achieves this by putting the antenna outside the Faraday cage: the GPS antenna is mounted at the very top of the fuselage, on the centreline, with an unobstructed view of the sky from horizon to horizon [5].
Your phone enjoys none of these advantages. Its patch antenna is a few square millimetres of copper on a PCB inside an aluminium-framed handset, typically held horizontally on your lap, under a tray table, under an overhead bin, inside a pressurised metal tube. The sky is geometrically reachable only through the nearest cabin window — and not even always then.
Because Xopoz uses the native Android LocationManager API directly (no Google Play Services, no cloud round-trip for the fix), the behaviour during a flight is entirely determined by what the phone's GPS chip can and cannot acquire. Expect the following sequence:
GPS typically works fine while the plane is parked at the gate with the doors open, or taxiing with the aircraft still oriented such that windows have some sky view. Your last valid fix and its timestamp are saved by Xopoz to the local encrypted position store. Use this opportunity to pre-cache the map tiles you might want to see en route.
Reception often degrades gradually during climb-out as the aircraft banks and manoeuvres. The window-seat rule kicks in: phones pressed to the window may still track; phones on tray tables typically lose the fix within a minute or two of wheels-up.
The map will continue to display — osmdroid draws whatever tiles are in its local cache — but the user cursor will remain frozen on the last valid fix. Xopoz does not fabricate positions; if the GPS chip reports no fix, nothing is recorded. The Android location provider will typically enter a TEMPORARILY_UNAVAILABLE state, which Xopoz reflects by keeping the cached location visible until a new fix arrives.
If you lean over to a window seat and hold the phone flat against the glass with the back of the handset (where most smartphone GPS patches are located) facing outward through the window, you can frequently obtain a fix within 30–90 seconds. This is a true satellite fix, with real altitude, real ground speed, and real bearing. Xopoz will happily record those positions if Local Save Permission is enabled.
Keep the Xopoz map screen on while doing this. Android aggressively throttles background location requests: when the screen is off or the app is not visible, the OS can downgrade GPS sampling to the low-power doze path, suspend location callbacks entirely, or defer them by minutes. By keeping the map open with the display on, you force the OS to honour the high-frequency GPS request Xopoz has registered, so every satellite fix that squeezes through the window is immediately delivered to the app and written to the local history. In a weak-signal environment like a cabin window, this difference between "sampled continuously" and "sampled once in a while" is often the difference between getting useful positions and getting nothing at all.
Reception usually returns before touchdown as the aircraft lines up with the runway and the windows point more upward. Positions resume being written to local storage. Once you re-enable cellular or Wi-Fi after landing, the Xopoz flush worker will push any offline positions to the team server on the next scheduled sync (see the Airplane Mode FAQ for details of the queue-and-flush model).
The same Faraday-cage physics applies to high-speed trains, with a twist: the train is at ground level, it passes through tunnels and cuttings, and it drags a powerful electromagnetic environment along with it.
In practice, a phone on a TGV or ICE travelling in open countryside with un-metallised windows can track position well. On trains with low-emissivity metallised glazing, or in tunnels, the fix is lost exactly as it is inside an airliner, for exactly the same reasons.
| Factor | Blocks GPS? | Explanation |
|---|---|---|
| Airplane mode (software) | No | Only disables transmitters (cellular/Wi-Fi/Bluetooth); GPS is receive-only and unaffected |
| Aircraft cruise speed (~250 m/s) | No | Well below the 515 m/s CoCom ceiling |
| Aircraft cruise altitude (~11 km) | No | Well below the 18 km CoCom ceiling |
| Aluminium fuselage | Yes | Acts as a Faraday cage; direct path from satellites is attenuated by tens of dB |
| Carbon-fibre fuselage (787/A350) | Yes (more) | CFRP absorbs RF energy; attenuation can exceed metal in some frequency bands |
| Distance from window | Partial | Signal leaks in through windows; seats more than ~1 m inside the cabin usually fail to fix |
| Coated or heated windows | Partial | Conductive coatings add further L-band attenuation |
| High-speed train body | Yes | Same Faraday-cage principle, plus tunnels, low-E glazing, and traction EMI |
| Aircraft's own navigation GPS | No | Antenna mounted on the roof, outside the shielded cabin, with full sky view |
| Xopoz when no fix is available | — | Map and last-known position remain visible; cursor freezes honestly until fix returns |