How Do Aircraft Use Distance Measuring Equipment (DME)?

In the days before electronic flight displays and modern flight instruments, distance measuring equipment (DME) served as a critical asset for conducting flight. As a radio system that could determine the distance between an aircraft and a VOR station, DME helped many pilots navigate much easier and safer. As the electronic flight display and modern flight instruments became more common, however, the original DME system quickly became outdated and the term eventually spread to include any navigation system that could provide accurate distance measurements to stations.

In the early days of aviation, many aircraft were fitted with one to two VOR receivers which relayed the bearing of the aircraft from the VOR station. While one could utilize an additional NAV receiver or a cross radial to determine distance from the station, the DME served as a simple solution that came in the form of small avionics equipment. Across most DME models, the general functionality allowed pilots to set a VOR frequency and receive distance identifiers in the form of audible sounds. In more advanced aircraft at the time, some DME equipment could have even been attached to a separate display to relay data visually.

To communicate with the VOR station, the DME sends out radio signal transmissions to the VOR ground station. Once received, the transponder of the station responds with a reply. As the reply reaches the aircraft, the DME unit will utilize the complete signal transmission time and determine the distance between the aircraft and the station in a straight line. For this simple, yet useful, process to be carried out, the VOR station would need to have the correct systems and apparatuses in place for such communication.

While the DME serves as a very convenient tool for safer flying, there are various downsides to such navigation systems. As stated before, the distance between the aircraft and the station is measured in a straight line, which is inaccurate for how aircraft operate. In reality, the aircraft will most likely be at a slanted line from the station due to its altitude, and thus the distance between the two is slightly inaccurate. As the aircraft ascends or reaches closer to the station, the inaccuracy of measurements only rises. Despite this, such issues tend to be minimal when farther away from the ground station and thus are rarely a major issue.

Nevertheless, a number of newer systems have come about since the original DME to further improve pilots’ abilities to navigate efficiently and map out their distances. After the DME, many avionics manufacturers began to implement area navigation systems, or RNAV systems, which gave pilots the ability to set a specified location for navigation. This greatly assisted the endeavors of many larger aircraft, as they could then operate on a wider variety of airways while still reaching their desired landing point.

After the RNAV system, global positioning systems quickly took the world by storm with their advanced navigational capabilities. By using satellite measurements as a distance indicator, pilots no longer needed to rely on VOR stations to travel from one point to the next. As such, the GPS system has become extremely commonplace in many aircraft, and may even legally replace a DME unit if certified and implemented correctly. 

While we have come so far since the original navigation systems relying on VHF communication, DME paved the way for more robust and safe equipment that we now rely on today. At Veritable Aviation, we can help you secure the navigation system parts and components that you need for your operations with ease. As a leading distributor of aviation parts and components, we can provide you with competitive pricing and rapid lead-times on over 2 billion new, used, and obsolete items that we carry. Get started today with a personalized quote when you fill out and submit an Instant RFQ form on our website.


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