MSA sectors

28.10.2004

Submission:

I have a question concerning MSA. To keep an RNAV ARR above MSA until established on the LLZ, I need to make a MSA SUBSECTOR based on a VOR called FLS. The existing MSA 25 nm sectors centred on FLS VOR are

360-090 DEG= 5400 FT

090-180 DEG= 5300 FT

180-360 DEG= 3300 FT

I would like to develop sub-sectors valid within 17 NM of FLS VOR and with the boundaries of:-

360-025 DEG= 3500 FT

025-140 DEG= 5300 FT

140-180 DEG= 3500 FT

180-360 DEG= 3300 FT

I will then have to publish two MSA boxes for the different DME distances from FLS VOR next to each other.

Can I take this practical approach or is it not recommended?

Ingar Lie, NATAM, ( PANS-OPS SECTION )

Norway

Answer or Commentary:

(I.W.

Normally the MSA sectors go out to 25 nm only and do not include inner sub-sectors (17nm). There are two ways that I can see that you could overcome this problem without using MSA sectors.

If you have Radar available you could develop radar-vectoring sectors inside the 25 nm MSA sectors. This will enable ATC to radar vector aircraft onto the Localizer at the correct interception altitude.

Or you could extend the initial approach segment out to 17 nm. You would then have to determine the most critical obstacle within the initial segment, obstacle protection areas and apply the applicable MOC.

Usually at major airports both ways are developed and used. I have never seen a MSA subdivided as suggested above but it may occur elsewhere in the world. Does anyone know of such a sub-division of MSA sectors existing?)