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

III-1-7-2 Procedures — Aircraft Operations — Volume II
23/11/06
7.5 XTT, ATT AND AREA SEMI-WIDTH
Cross-track and along-track tolerances (XTT and ATT) are equal to the RNP value.
RNP area semi-width is determined by the formula:
2×XTT+BV
where:
BV = buffer value (see Table III-1-7-1)
Note — The buffer values are derived from an assessment of the worst case maximum excursion beyond the ANP
alarm limits generated by the RNP system.
Example calculation
The calculation for RNP 1 departures is shown below.
XTT = 1.85 km (1.00 NM)
BV= 0.56 km (0.30 NM)
area semi-width =
2 × 1.85 + 0.56 = 4.26 km
2 × 1.00 +0.30 = 2.30 NM
Table III-1-7-1. RNP buffer values
Segment Buffer value (BV)
Departure 0.93 km (0.50 NM)
En route 1 and arrival 2
1.85 km (1.00 NM)
Arrival 3 /initial/intermediate approach 0.93 km (0.50 NM)
Final 0.37 km (0.20 NM)
Missed approach 0.56 km (0.30 NM)
Holding 4
1. For all RNP types equal to or exceeding RNP 1.
2. Arrivalupto46km(25NM)beforetheIAF.
3. Arrival closer than 46 km (25 NM) to the IAF.
4. Holding areas use different principles.
Note.— The buffer values in Table III-1-7-1 are derived from an assessment of the worst case maximum excursion
beyond the ANP alarm limits generated by the RNP system.
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