Precision or Non-Precision ILS

14.03.2007

Submission:

(I.W.

 I had an interesting situation a while back. How does one analyse obstacles in an ILS approach when the FAF/FAP is before the beginning of the 300m precision segment. As in the following diagram:

 Diagram 1

1./        Treat that portion (see shaded area in following the diagram) as if it is a LLZ only approach and apply a MOC of 75m even though the aircraft has LLZ and GP information. Then you may have a step down fix in an ILS approach??

 Diagram 2

2./        Or extend the OAS contour out to the FAF/FAP as in the following diagram. However that also extends the “Y” surfaces and makes the protection area larger than the previous example.

 Diagram 3

Any thoughts?)