The scope of this specification covers all the provisions necessary to enable communication of large messages between airborne and ground applications without degradation of the availability required of air-ground links to deliver Air Traffic Service (ATS) messaging in a timely manner.

This standard defines a communication protocol for air-ground communications aiming at:

• Exchanging AOC messages of any type between aircraft and ground to take place over ARINC 618 networks, without current networks limitation (e.g., 3360 bytes maximum size limitation for ACARS downlinks, 3520 bytes for ACARS uplinks)

• Allowing existing ARINC 620 AOC exchanges between ground and aircraft to occur over IP networks

The standard is intended to be used only for AOC exchanges, but its design should not preclude future use by Air Traffic Control (ATC).

Purpose of Document

The purpose of this document is to provide an industry standard for Media Independent Aircraft Messaging (MIAM) which permits the exchange of a large volume of data over Aircraft Communications Addressing and Reporting System (ACARS) subnetworks or broadband Internet Protocol (IP) subnetworks.

The volume of data transmitted over ACARS data link is increasing, notably on new generation aircraft. Although availability of new IP-based communication systems provides additional communication paths, ACARS will continue to be used for Aeronautical Operational Control (AOC) message transmission.

There is thus a need for a protocol that allows avionic systems to exchange large volumes of data (larger than maximum ACARS message) over ACARS subnetworks (VHF Digital Link Mode 2 (VDL2) or traditional ACARS subnetworks under certain conditions) as well as broadband IP subnetworks.

ARINC Specification 841 was developed to:

• Improve ACARS performance and efficient Radio Frequency (RF) spectrum utilization

• Define a communication service common to ACARS and IP subnetworks

• Provide ACARS access to new data link users (e.g., Electronic Flight Bag (EFB) applications)

• Avoid proliferation of proprietary solutions