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Old 15th Aug 2015, 03:04
  #66 (permalink)  
Join Date: Sep 2011
Location: Mercer Island WA
Posts: 139
@CM ...Not so

CM,... Not so. The fact that a system may have an ANP adequate to fly a "GNSS only" approach means absolutely NOTHING in an RNP world. ANP must always be less than, and be predicted to stay less than, the specified level of RNP (even for non-normals) for the specific RNP based procedure to be flown, with adequate FTE margin. Further, your assertion about "RNAV approaches with LNAV and VNAV minima" has nothing whatsoever to do with RNP based RNAV procedures (e.g., NZQN RNAV(RNP) RWY23). This discussion relates purely to those kinds of RNP based procedures, and is a subject for which no current BizAv based avionic system, as typically used in any RJ presently flying, comes anywhere close to meeting RNP.1 capability, for the leg types and configurations of the RNP based approaches noted, or duplicating the key capability needed to address rare normal and non-normal conditions for those procedures, as I cited earlier. I'm not aware of ANY RJ currently capably of flying RNP based procedures at low RNP values near or at RNP .1, such as needed at NZQN or PAJN, let alone for meeting the VEB related to the vertical RNPs associated with those procedures. In fact from what I've seen in recent months for design specifications for AFDS and FMS system improvements in the RJ fleets, and for even a few new designs in development in that class, this full equivalent RNP capability that has been flying in the big jets for years isn't likely to happen at any time soon in the RJ fleet, in even the intermediate future. Further, even the basic fundamental avionics architecture is weak in some of these RJ designs, potentially even permanently precluding beneficially combining use of modes for LAND 3 using GLS, also with low RNP capability.
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