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

II-1-1-14 Procedures — Aircraft Operations — Volume II
23/11/06
1.4.9 Obstacle clearance of the precision segment — application of collision risk model (CRM)
1.4.9.1 General. The CRM is a computer programme that establishes the numerical risk which can be compared
to the target level of safety for aircraft operating to a specified OCA/H height. A description of the programme and
instructions on its use, including the precise format of both the data required as input and the output results, are given in
the Manual on the Use of the Collision Risk Model (CRM) for ILS Operations (Doc 9274).
1.4.9.2 Input. The CRM requires the following data as input:
a) aerodrome details: name, runway threshold position and runway orientation in threshold elevation above MSL,
details of proceeding segment;
b) ILS parameters: category, glide slope angle, localizer-threshold distance, localizer course width, height of ILS
reference datum above threshold;
c) missed approach parameters: decision height (obstacle clearance height) and missed approach turn point;
d) aircraft parameters: type, wheel height (antenna to bottom of wheel), and wing semi-span, aircraft category (A,
B, C, D or DL) missed approach climb gradient; and
Note.— The CRM does not consider Category E aircraft.
e) obstacle data: obstacle boundaries (either as x and y coordinates relative to the runway threshold or as map grid
coordinates) and obstacle height (either above threshold elevation or above MSL). For density assessment, all
obstacles penetrating the basic ILS surfaces described in 1.4.7.2 must be included.
1.4.9.3 Output and application. The output of the programme is:
a) the overall (total) risk of collision with obstacles for aircraft operating to a specified OCA/H; and
b) the minimum OCA/H which will provide the target level of safety.
The user, by rerunning the CRM with the appropriate parameters, can assess the effect on the safety of operations of
any alteration in the parameters, typically varying the glide path angle or remaining obstacles.
1.5 MISSED APPROACH SEGMENT
1.5.1 General
1.5.1.1 The criteria for the final missed approach are based on those for the general criteria (see Part I, Section 4,
Chapter 6). Certain modifications have been made to allow for the different areas and surfaces associated with the
precision segment and for the possible variation in OCA/H for that segment with aircraft category. Area construction is
according to the navigation system specified for the missed approach.
1.5.1.2 The datum used for calculation of distances and gradients in obstacle clearance calculations is termed
“start of climb” (SOC). It is defined by the height and range at which the plane GP’— a plane parallel with the glide
path and with origin at –900 m (Cat H, –700 m) at threshold level — reaches the altitude OCA/H – HL. OCA/H and
HL must both relate to the same category of aircraft.