GPS Off DEMO
Location is blocked on this page, so the DME has no position to measure from.
Lamp test
Install Pocket DME on this phone so it opens full screen and works offline in the cockpit.
No altitude yetWaiting for GPS
The app keeps the difference between your figure and GPS, and applies it as you climb and descend.
Simulated DMEs for teaching. They stay on this phone. Tap one in the list to tune it.
TST on 108.00, here
Puts DME TST at your exact present position and altitude on 108.00 MHz and tunes to it. Set it on the ground so it sits at ground level. Press again to move it.
Add a DME by position
Latitude as N521132 or 52.1922, longitude as W0013652 or -1.6144. Frequencies are given in turn from 108.05 upwards, skipping those used by real stations.
Flies a simulated aircraft at 100 kt and 3,000 ft with a 250/15 wind, heading for the tuned station, so you can try the DME on the ground. Drag sideways across the display to turn; use ALT to climb or descend.
Tap one to tune it.
Set the station’s frequency on the drums: MHz, then tenths and hundredths. The DME channel shows beside them. Press DME: the display tests itself, shows dashes while it searches, then locks on.
NM is the slant range, the straight-line distance from the aircraft to the station. KT is how fast that distance is changing, and MIN is the time to the station at that speed. MIN shows dashes while the distance is increasing.
KT and MIN are only right when you fly straight to or from the station. On a DME arc KT reads close to zero.
If the signal is lost the DME holds its reading for about 10 seconds (MEM lights), then shows dashes and searches again.
IDENT switches the station’s Morse ident on and off: a 1350 Hz tone. Here it repeats every 10 seconds; a real DME sends it about every 30.
TEST lights every segment and shows how good the GPS fix is. A red GPS flag means there is no position; a red ALT flag means there is no altitude (set one with ALT).
Menu holds practice DMEs, altitude, ident volume, a demo flight and the stations near you.
The app works out the slant range in three dimensions: from your GPS position and altitude to the station’s position and published elevation. Overhead the station the DME reads your height above it, about 1 nm for every 6,000 ft.
Rule of thumb: slant range error is small once you are at least 1 nm from the station for every 1,000 ft you are above it.
PROFILE shows the geometry: ground distance, height above the DME, slant error (slant range less ground distance) and GPS ground speed to compare with KT. Switch it off to fly on the DME alone.
GPS altitude is often within 50 to 100 ft, but can be worse. If it is wrong, tap ALT and enter what the altimeter reads on QNH, or the airfield elevation while on the ground. The app keeps the difference and applies it as you climb and descend. Use GPS altitude clears it, and a correction is forgotten after 6 hours.
Android phones give height above the WGS84 ellipsoid, which the app turns into altitude above sea level with the EGM96 geoid (150 to 185 ft in the UK). iPhones give altitude above sea level already. With no GPS altitude at all, the altitude you enter is used as it stands.
In Menu, Set TST here puts DME TST on 108.00 at your exact position and present altitude, and tunes to it, so a student can fly away from it and back. Add a DME by position takes an ident, a latitude and longitude, and the station’s elevation, and gives it the next free frequency from 108.05 upwards. WSB at Wellesbourne, elevation 159 ft, is there as an example. Practice DMEs are received anywhere within 200 nm, at any height.
Real stations need line of sight: roughly 1.23 × (√ your altitude + √ station height) nm, with heights in feet, and they are limited to 50, 100 or 200 nm by power. Low down or far away, the DME stays on dashes. In Stations near you, stations out of reach at your altitude are greyed out.
Close to the station the DME always reads more than the ground distance. That is slant range, not a fault.
Training aid only. This is not a navigation instrument and must not be used as one.
Stations come from the OurAirports database (downloaded November 2026): VOR/DMEs, TACANs, DMEs and NDB/DMEs in the UK, Isle of Man and Channel Islands. ILS DMEs are not included. Some stations may since have been withdrawn, so check the UK AIP before relying on one. Magnetic variation is from the WMM2025 model; sea level is from the EGM96 geoid.
Audio: on iPhone, ident audio needs the ringer on unless your iOS supports playback mode. Plug into the intercom or use Bluetooth for headset audio.
Copyright J Wilby 2026