 It was the same as VDL Mode 2 except that it used the same VHF link as VHF ACARS so it could be implemented using analog radios before VHF Digital Radio implementation was completed.The ICAO AMCP completed validation of VDL Modes 1&2 in 1994, after which the Mode 1 was no longer needed and was deleted from the ICAO standards.The ICAO VDL Mode 2 is the main version of VDL.