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

II-1-1-App D-2 Procedures — Aircraft Operations — Volume II
b) maximum 45° break-out angle.
2.2 Due to the nature of the surfaces, these two parameters are interdependent. During the evaluation, it was
found that the lower the break-out was considered, the earlier the assessment surfaces would be penetrated, causing the
break-out angle to be reduced, e.g. a minimum break-out height of 60 m (200 ft) would result in a break-out angle of
20°, and a minimum break-out height of 300 m (1 000 ft) would result in a break-out angle of 65°.
2.3 It was considered necessary to restrict the minimum break-out altitude/height. One reason was that break-out
manoeuvres at too low heights could be considered unsafe. Moreover, considering the maximum assumed blunder
angle of 30° and approach speed of 150 kt, it could be assumed that below a certain height the blundering aircraft could
not reach the threatened aircraft before it landed. and therefore it would be of no use to protect for these low heights.
2.4 Information available in respect of flight and simulator tests conducted by one State for these manoeuvres
showed that phraseology used by the air traffic services (ATS) was similar to that contained in the PANS-ATM,
Chapter 12, on independent parallel approaches. Following the instructions from air traffic services, the pilot actually
first arrested the descent and then established climb, crossing the glide path (if below) before turning. This information
supported the assumptions used to validate the proposed obstacle assessment criteria.
2.5 The evaluation report further indicated that it was not considered convenient to provide additional obstacle
assessment surface (OAS) constant tables in PANS-OPS for these cases for each localizer-threshold distance
combination. The proposed surfaces are based on operational rather than statistical considerations. Therefore, it was
proposed to use one set of surfaces for all combinations of localizer-threshold distances. These surfaces would
guarantee protection for aircraft following the assumed operational scenario.
2.6 A mathematical match was made from the surfaces for an average runway length/localizer distance contained
in the Federal Aviation Administration (FAA) Order (8260.41). This approach was considered acceptable for the
assessment of rare events for which statistical analysis was not feasible.
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3. APPLICATION OF PARALLEL APPROACH OBSTACLE
ASSESSMENT SURFACE (PAOAS) CRITERIA
3.1 General
In addition to the application of OAS criteria specified in Chapter 1, 1.4.8, “Obstacle clearance of the precision
segment using (OAS) criteria,” parallel approach obstacle assessment surfaces (PAOAS) are defined to safeguard the
execution of an immediate climb and turn manoeuvre to the assigned heading and altitude/height. PAOAS criteria are
used to demonstrate obstacle clearance, accommodating turns up to 45° from the approach path and a lowest break-out
manoeuvre initiation of 120 m (400 ft) above threshold elevation. PAOAS criteria are valid for all categories of
instrument landing system/microwave landing system (ILS/MLS) approaches.
3.2 Definition of surfaces.
3.2.1 The PAOAS consists mainly of two sloping plane surfaces (denoted P1 and P2) positioned on the side of the
runway opposite to the adjacent runway. The geometry of the sloping surfaces is defined, similar to the OAS surfaces
(see Chapter 1, 1.4.8.4, “Definition of obstacle assessment surfaces (OAS)”) by a linear equation of the form z = Ax +
By + C. The constants are related to the glide path angle only. They are independent of the category of ILS/MLS
operations and localizer-threshold distance. The constants are given in Table II-1-1-App D-1.