Initial RNAV turn

02.10.2009

Submission:

I. W.

Previously in Pans-Ops the initial segment of an RNAV approach did not use wind spirals on the inside of the turn. Now wind spirals are used from both latest turning points. Sounds very reasonable and looks very reasonable in the diagram.



However it only looks reasonable if the initial waypoint is further than 8nm from the intermediate waypoint. When the initial waypoint is closer the initial segment protection area spills over into the intermediate and final segments. The obstacle protection area can even include area passed the missed approach waypoint.



If we are protecting an area it means that an aircraft could be there. Is it reasonable to protect an area significantly passed the IWP and would an aircraft ever be there during the initial phase of flight? A RNAV equipped aircraft would have to fly past the IWP, FAWP and the MAWP to be in that position.

Has any one else got any ideas, could this really happen?

Answer or Commentary:

I agree with Ian, that it is virtually impossible to construct a ‘standard’ RNAV procedure.

My own ‘solution’ is that I don’t use the 2nd wind spiral on turns of 90° or less. Figures III-2-2-2 and III-2-2-5 in Pans-Ops essentially show a similar turn, but are substantially different, and very confusing. The former shows N” drawn at ATT from the turn bisector, the latter show N” drawn at ATT from the bisector, but originating along the latest turning point line.

Jerry Willmot – procedure designer
Airways Corporation – New Zealand