# Background - DME allows for aircraft to determine their approximate distance from a VOR - More information can be found from the [FAA: DME Information](https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gbng/lpdme) ![[DME on VOR image.png]] ## How DME Works - The equipment on an aircraft sends out a signal to the ground equipment - based on the amount of time it takes to get a response, the equipment can calculate the aircrafts approximate distance from the station $ Distance \space from \space station = \frac{1}{2} \times time \space to \space get \space response \space (hours) \times 582,749,918 $ - 582,749,918 is the approximate speed of light in knots # DME Accuracy - DMEs are quite accurate, but they *DO NOT* calculate an aircrafts distance across the ground from a station - We call the distance that DMEs display *slant distance* because they display an aircrafts distance if it went directly to the VOR - DMEs should not be used when the airplane is less than 1NM away from the station for every 1,000 ft of altitude ## Calculating Distance Across the Ground $ Distance = \sqrt{DME \space measurement^2\space - \space altitude^2} $ - Note that you would have to convert your altitude *above the station* to nautical miles for the calculation to be accurate # Identifying DME - When a VOR and DME are co-located (VORTAC or VOR-DME) the DME transmits the same identifier as the VOR, but during the pause between VOR idents - The DME ident is usually played between every $3^{rd}$ or $4^{th}$ VOR identifier - The DME ident is higher-pitched - DME: 1350 Hz - VOR: 1020 Hz ![[Pasted image 20240204122504.png]]