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Old 15th Aug 2013, 18:07
  #146 (permalink)  
PEI_3721
 
Join Date: Mar 2006
Location: England
Posts: 848
OK465. Thanks for the chart explanation (#132 / 135), although I am surprised by the accuracy difference between LOC (an angular system) and GPS RNAV (linear, RNP 0.3); I also note that BIDPE is a waypoint in the GPS procedure.
However, it still appears illogical for the RNAV approach to allow a descent to 2600ft (well below a constant-angle path), when such a relatively new procedure could have been constructed to help improve safety.

As Airbubber notes, most modern installations use the GPS receiver built into EGPWS; however this is not used for navigation. Other EGPWS configurations still depend on an external nav input, which even with GPS (used for nav) is only assumed to correctly represent the aircraft’s position, i.e. GPS drop out / error, the nav position could ‘slip’.
Depending on the aircraft’s nav installation, some of the early EGPWS installations could suffer map slip, which could falsely position the aircraft in the EGPWS safe area before the runway, and the in-parallel standard GPWS function would not warn of low terrain due to the landing configuration – gear and flap.
Thus what was the EGPWS nav configuration in this aircraft?
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