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RNP AR non precision approach procedures are RNAV approach procedures where, to my understanding, RNP is below 0.3 NM and down to 0.1 NM, GPS is required and a special authorization is required for the operator (airline + crew + a/c tech status).
I understand that, for this kind of operation, besides the relevant RNAV approach authorization, a special authorization has to be issued by the State Authority in charge of the relevant airport.
I've checked the A320 FCOM and it states that operators are responsible for drawing contingency procedures for RNP AR NPAs.
Does any of you have any idea on when one can find an overwiew of these contingency procedures? I mean, just to have an idea on what are the actions required to perform a missed approach and to mantain the required obstacle clearence while experiencing navigation accurancy problem.
Thanks!
RNP AR IAPs can have a line of minima as high as 0.30 and as low as 0.10. Also, the missed approach can be conventional TERPS or PANS-OPS missed approach criteria or it can be an RNP missed approach. An RNP missed approach is "telescopimg" RNP segments, which presumes at least one IRU to maintain positioning throughout the missed approach in the event of loss of GPS, albeit degrading position information, thus the reason for the "telescoping" expansion.
Also, if a line of minima is used that is less than RNO 0.30 then at least one IRU is required for that purpose, independent of the missed approach construction.
So, only on an RNP 0.30 procedure with a conventional missed approach could position be lost unless a dual failure occurs (loss of GPS and IRU(s) ). Because most airplanes have 3 IRUs, this event is highly unlikely.
Here is an RNP AR procedure that does not require any IRU(s), so the loss of GPS could cause the wings to level during the final segment RF leg, thus pointing you at very high terrain.
http://aeronav.faa.gov/d-tpp/1302/05737RR30.PDF
A properly trained crew should revert to the departure procedure for this airport, which would mandate rolling back into the turn and proceeding directly to the BIH VOR to pick up the departure procedure.
If the VOR were out of service that day, then turning towards the airport, then when overhead establishing a heading the same as the departure procedure, should make a DR heading sufficently safe to fly into a less critical area of terrain.