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

Part III — Section 3, Chapter 6 III-3-6-11
c) Determine which of the obstacles identified in steps a) and b) is the highest. This will give the controlling
obstacle.
d) Add the appropriate aircraft category related margin (Table III-3-6-3) to the height of the highest controlling
obstacle.
ha =
hma cot Z + (–xz +x)
cot Z + cot θ
where: ha = height of equivalent approach obstacle
hma = height of missed approach obstacle
θ = glide path angle
Z = angle of missed approach surface
x = range of obstacle relative to landing threshold point (negative after LTP)
xz = distance from threshold to origin of Z surface (–900 m, –700 m for Cat H)
6.4.8.8.3 Adjustments for high airfield elevations and steep glide path angles.
6.4.8.8.3.1 The margins shall be adjusted as follows:
a) for airfield elevation higher than 900 m (2 953 ft), the allowances shall be increased by 2 per cent of the radio
altimeter margin per 300 m (1 000 ft) airfield elevation; and
b) for glide path angles greater than 3.2° in exceptional cases, the allowances shall be increased by the 5 per cent
of the radio altimeter margin per 0.1° increase in glide path angle between 3.2° and 3.5°.
6.4.8.8.3.1.1 Procedures involving glide paths greater than 3.5° or any angle when the nominal rate of descent (Vat
for the aircraft type × the sine of the glide path angle) exceeds 5 m/sec (1 000 ft/min), are non-standard. They require
the following:
a) increase of height loss margin (which may be aircraft type specific);
b) adjustment of the origin of the missed approach surface;
c) adjustment of the slope of the W surface;
d) re-survey of obstacles; and
e) the application of related operational constraints.
Such procedures are normally restricted to specifically approved operators and aircraft, and are associated with
appropriate aircraft and crew restrictions. They are not to be used as a means to introduce noise abatement procedures.
6.4.8.8.3.1.2 Part II, Section 1, Chapter 1, Appendix B shows the procedure design changes required and the
related operational/certification considerations.
23/11/06