ACARS ([A]ircraft [C]ommunication [A]ddressing and [R]eporting ystem) is a digital data link system transmitted via VHF radio which allows airline flight operations departments to communicate with the various aircraft in their fleet.
This VHF digital transmission system, used by many civilian aircraft and business jets, can be likened to "email for airplanes," as the registration of each aircraft is it's unique address in the system developed by aeronautical radio giant ARINC (Aeronautical Radio, Inc.). Traffic is routed via ARINC computers to the proper company, relieving some of the necessity for routine voice communication with the company. With ACARS, such routine items as departure reports, arrival reports, passenger loads, fuel data, engine performance data, and much more, can be requested by the company and retrieved from the aircraft at automatic intervals. Before the advent of ACARS, flight crews had to use VHF to relay this data to their operations on the ground.
