NDB minima.
And you are correct, you could follow the ILS completely on RNAV. Having both displayed on the PD, the only time they really deviate is at the bottom as the VNAV is using the piano keys as a reference.
With RNP at less than 0.3 or better in approach phase conducting a LOC/VOR/RNAV/GNSS is fine. The last two have no reference aid at all. And the last one is for the Seychelles (CAT C) sliding along the mountain range in a turn on to short finals, or for JFK for 13L/13R to near CAT I minima.
However performing a line-selectable NDB approach without an ADF, but with RNP usually around 0.1 or better seems daunting.
NDB approaches have huge tolerances built in. If there was little room for error then another aid/approach would be there instead.
And it's not my logic. It's the way things are changing toward.
Believe me, if the NAV SYS fell over and the only approach available was an NDB, l would be wanting ADF's there in front of me. But l guess that is a calculated risk by the manufacturer, the company and regulator.
halas
ps: For those not familiar... Line-selectable means the approach that is desired is available in the aircraft nav data base which is updated every 28 days.
This is validated against the chart for the same approach for distances, bearings, speed limits, timing, altitude constraints and temperature.
RNP 0.3 equals 0.3 of one nautical mile before an alert for UNABLE RNP is sounded.
Last edited by halas; 16th January 2012 at 21:23.