There are around 15 HF ground stations (HGS) available today, and, like a canopy within a jungle, the stations provide overlap and redundancy in the unlikely event of a HGS failure. Today, HFDL is an air/ground data link standard with coverage in virtually every corner of the globe, approximately 168,000,000 square miles (440,000,000 km 2) where aircraft are never out of touch both in the air and on the ground. The CMU is an airborne communications router that interfaces with many aircraft communications systems including SATCOM, VHF, HFDL, FMS and others. To use the service, an aircraft only needs a Communications Management Unit (CMU), or equivalent and an HFDL data radio. As a result, pilots can always communicate with someone on the ground.
Using the unique propagation characteristics of high-frequency radio waves, the ground stations provide data link communications to properly equipped aircraft operating anywhere in the world. High Frequency Data Link ( HFDL) is an ACARS communications medium used to exchange data such as Aeronautical Operational Control (AOC) messages, Controller Pilot Data Link Communications (CPDLC) messages and Automatic Dependent Surveillance (ADS) messages between aircraft end-systems and corresponding ground-based HFDL ground stations. ( May 2013) ( Learn how and when to remove this template message) This article may have too many section headers.
