RWA - The ACARs messages go via any of one 4 (soon to be 7) operation Inmarsat sateliites (plus backups). The SATCOMs is continously tracking the satellite on which the A/C has logged-on. The Inmarsat Aero air-interface should allow any ACARS messages to be transmitted within a few seonds in normal circumstances and certainly in less than a minute if the Ground Earth Station is operating normally.