1.1.1.1 Downlink Message Delivery-Sequence of Events
1. If VHF is available,FANS-1/A aircraft will attempt to deliver messages through one VHF RGS only.If this attempt fails,delivery will be attempted via SATCOM.Where VHF is not available and the aircraft is in VHF NOCOMM mode,delivery will only be attempted via satellite.
Note:For non time-sensitive traffic,(satellite-equipped) aircraft operating in (VHF)CAT-B mode will usually attempt to deliver messages through three VHF BGSs before reverting to satelite.
2. The DSP will extract the address of the CAA to which the message shall be delivered.This address is contained in the supplementary address field of the message.The message shall now be in Type-B format.
Note:If required an airlines can request that FANS-1/A datalink messages are also delivered to a pre-configured address.Usually,however messages are only delivered to the intended CAA,as indicated by the supplementary address contained in the downlink message.
