A056 LOAs can be issued for FANS 1/A+ (oceanic), ATN B1 (European over land), or both depending on how the aircraft is equipped. A056 requests are initially submitted to the Operator’s local FSDO via email or USB drive. The FSDO inspectors conduct an initial review, then the request is uploaded to a regional navigation specialist for more in-depth review.
Part 91 A056 LOAs are not required for US domestic datalink operations or European ATN B1 operations.
NAT Data Link Mandate (DLM) requires aircraft to be equipped with, and operating, CPDLC and ADS-C in the NAT region. Currently, the mandate incorporates FL290 to FL410 inclusive. The FAA's A056 LOA is required to conduct operations in Datalink Mandate airspace in the North Atlantic.
DLM is not applicable to aircraft operating in:
a) Airspace north of 80° North (see map below);
b) New York Oceanic East flight information region (FIR);
c) Airspace where an ATS surveillance service is provided by means of radar, multilateration and/or ADS-B, coupled with VHF voice communications as depicted in State Aeronautical Information Publications (AIP), provided the aircraft is suitably equipped (transponder/ADS-B extended squitter transmitter)
The ICAO North Atlantic Operations and Airspace Manual provides extensive information on operational requirements for the North Atlantic, including Datalink Mandate (DLM) Airspace.
Below is a map of non-DLM airspace (extracted from NAT DOC 007 V Jan 2022):