Aircraft Operations. Volume II - Construction of Visual and Instrument ...

Part II — Section 1, Chapter 1 II-1-1-5
1.3.1.2 The primary and secondary areas at the FAP are defined in terms of the ILS surfaces. Consequently, the
general criteria in Part I, Section 4, Chapter 4, “Intermediate Approach Segment” are applied except as modified or
amplified in the paragraphs below with regards to alignment, area length and width, and for obstacle clearance. For
RNAV initial approach segments, the criteria in the applicable RNAV chapters apply.
1.3.2 Intermediate approach segment alignment
The intermediate approach segment of an ILS procedure shall be aligned with the localizer course.
1.3.3 Intermediate approach segment length
1.3.3.1 The optimum length of the intermediate approach segment is 9 km (5 NM) (Cat H, 3.7 km (2 NM)). This
segment shall allow interception with the localizer course and with the glide path.
1.3.3.2 Segment length should be sufficient to permit the aircraft to stabilize and establish on the localizer course
prior to intercepting the glide path, taking into consideration the angle of interception with the localizer course.
1.3.3.3 Minimum values for distance between localizer and interception of glide path are specified in
Table II-1-1-1; however, these minimum values should only be used if usable airspace is restricted. The maximum
length of the segment is governed by the requirement that it be located wholly within the service volume of the
localizer signal and normally at a distance not exceeding 46 km (25 NM) from the localizer antenna.
1.3.4 Intermediate approach segment area width
1.3.4.1 The total width at the beginning of the intermediate approach segment is defined by the final total width of
the initial approach segment. It tapers uniformly to match the horizontal distance between the OAS X surfaces at the
FAP (see 1.4.8.4, “Definition of obstacle assessment surfaces (OAS)”).
1.3.4.2 For obstacle clearance purposes the intermediate approach segment is usually divided into a primary area
bounded on each side by a secondary area. However, when a DR track is used in the initial approach segment, the
primary area of the intermediate approach segment extends across its full width and secondary areas are not applied.
1.3.4.3 The primary area is determined by joining the primary initial approach area with the final approach
surfaces (at the FAP). At the interface with the initial approach segment the width of each secondary area equals half
the width of the primary area. The secondary area width decreases to zero at the interface with the final approach
surfaces. See Figures II-1-1-1, II-1-1-2 and II-1-1-3.
1.3.4.4 Where a racetrack or reversal manoeuvre is specified prior to intercepting the localizer course the
provisions in Part I, Section 4, Chapter 4, 4.4.4, “Turn not at the facility” apply, the facility being the localizer itself
and the FAF being replaced by the FAP. (See Figure II-1-1-4.)
1.3.5 Intermediate approach segment obstacle clearance
The obstacle clearance is the same as defined in Part I, Section 4, Chapter 4, “Intermediate approach segment” except
where the procedure permits a straight-in approach in which the aircraft is stabilized on the localizer course prior to
crossing the IF. In this case, obstacles in the secondary areas need not be considered for the purpose of obstacle
clearance.
23/11/06