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

Appendix C to Chapter 3
CONSTRUCTION OF OBSTACLE CLEARANCE
AREAS FOR REVERSAL AND HOLDING PROCEDURES
1. INTRODUCTION
The construction of obstacle clearance areas for reversal procedures (Part III, Section 3, Chapter 7) is based on the
direct application of the tolerance criteria specified in Part I, Section 2, Chapter 2. These may be applied either on an
additive tolerance basis, or using statistical methods.
2. STATISTICAL AREA CONSTRUCTION
If statistical methods are used to combine the variables and then to extrapolate distributions to develop areas, the
probability level associated with that extrapolation should meet an acceptable level of safety.
3. ADDITIVE TOLERANCE AREA CONSTRUCTION
A variety of methods may be used; whichever method is used, the criteria and parameters given in 3.5 of Part III,
Section 3, Chapter 7 apply. The method described in this attachment is the template tracing technique (TTT).
3.1.1 General
3.1 Protection area of a base turn
The primary area of a base turn can be drawn either by applying the construction method of the template specified in
3.1.2 of this attachment or by using one of the precalculated templates contained in the Template Manual for Holding,
Reversal and Racetrack Procedures (Doc 9371) for the appropriate timing, speed and altitude. This template caters for
all factors which can cause an aircraft to deviate from the nominal track, tolerances of the navigational facility, flight
technical tolerances and wind effect, so that it represents the primary area of the base turn.
3.1.2 Construction of the base turn template
3.1.2 (Reference Table I-4-3-App C-1 and
3.1.2 Diagram I-4-3-App C-1)
3.1.2.1 Draw a line representing the axis of the procedure and locate point “a” on the fix — draw the nominal
outbound leg and inbound turn:
— angle between outbound leg and procedure axis: θ (Table I-4-3-App C-l, line 10)
I-4-3-App C-1 23/11/06