RogerRamjet01
12th May 2009, 09:27
I have a question for the more experienced IFR RNAV (GNSS) users out there.
IS there a firm, legal requirement to perform an inflight RAIM prediction?
During my instrument rating I was taught to obtain a RAIM prediction using the reciever (TSO 129) once within 30nm and prior to commencing track / descent for the RNAV approach. But I cannot for the life of me find the documented basis for this.
I realise there is a requirement to assess RAIM / FDE for flightplanning purposes, and that this wil impact selection of alternates if you have TSO 145 / 146 equipment in the aircraft (and that if you have TSO129 equipment then you cannot use the GPS to satisfy alternate requirements anyway).
However after hunting through the relevant CAAPs and CAOs, as far as INFLIGHT RAIM availability / prediction is concerned, I can only find statements to the effect that RAIM must be "available" prior to descent below LSALT, and that a missed approach must be commenced if a RAIM warning appears.
CAAP 179a(1) mentions that the equipment automatically performs a prediction for the approach, and will not enter approach mode until RAIM is to predicted to be available. That document (section 8) also specifically mentions the limitations of reciever based predictions compared to the ones you find attached to the Met briefings (I am guessing because the latter include GPS notams issued since the last GPS almanac issue).
So wouldnt it be more accurate in any case to do your RAIM / FDE prediction using the Airservices data preflight?
Please note I am not casting in doubt the wisdom of doing a double check RAIM prediction prior to an RNAV approach - I am just wondering if there is a requirement for it in law.
Any comments / thoughts appreciated.
IS there a firm, legal requirement to perform an inflight RAIM prediction?
During my instrument rating I was taught to obtain a RAIM prediction using the reciever (TSO 129) once within 30nm and prior to commencing track / descent for the RNAV approach. But I cannot for the life of me find the documented basis for this.
I realise there is a requirement to assess RAIM / FDE for flightplanning purposes, and that this wil impact selection of alternates if you have TSO 145 / 146 equipment in the aircraft (and that if you have TSO129 equipment then you cannot use the GPS to satisfy alternate requirements anyway).
However after hunting through the relevant CAAPs and CAOs, as far as INFLIGHT RAIM availability / prediction is concerned, I can only find statements to the effect that RAIM must be "available" prior to descent below LSALT, and that a missed approach must be commenced if a RAIM warning appears.
CAAP 179a(1) mentions that the equipment automatically performs a prediction for the approach, and will not enter approach mode until RAIM is to predicted to be available. That document (section 8) also specifically mentions the limitations of reciever based predictions compared to the ones you find attached to the Met briefings (I am guessing because the latter include GPS notams issued since the last GPS almanac issue).
So wouldnt it be more accurate in any case to do your RAIM / FDE prediction using the Airservices data preflight?
Please note I am not casting in doubt the wisdom of doing a double check RAIM prediction prior to an RNAV approach - I am just wondering if there is a requirement for it in law.
Any comments / thoughts appreciated.