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leg from the FROP to PFAF can be calculated by formula 3-12.
Formula 3-12
LengthRF = DPFAF −DFROP
Example
FROP
where DPFAF = 29147.45 (from formula 3-9)
D = 8548.35 (from formula 3-10)
LengthRF=29147.45−8548.35 = 20599.10
8260.52 6/3/05
Page 3-10 Par 3.4.2
The number of degrees of arc given a specific arc length may be calculated using
formula 3-13.
Formula 3-13
Degrees of Arc [ ]: 180 L
R
φ φ
π
⋅
=
⋅
Conversely, the length of an arc given a specific number of degrees of arc may
be calculated using formula 3-14.
Formula 3-14
Length of Arc [L]:
180
L R
φ⋅ π ⋅
=
3.4.2 a. Determining RF PFAF Location Relative to LTP. This method may be
used for calculating WGS-84 latitude and longitude (see figure 3-3). Several
software packages will calculate a geographical coordinate derived from
Cartesian measurements from the LTP. Use formulas 3-15 and 3-16 to obtain
the Cartesian values.
STEP 1: Determine the flight track distance (DPFAF) from LTP to PFAF under
formula 3-9.
STEP 2: Determine the distance (DFROP) from LTP to the FROP (see paragraph
3.3).
STEP 3: Subtract DFROP from DPFAF to calculate the distance around the arc to
the PFAF from the FROP. Use formula 3-13 to determine number of degrees of
arc; conversely, use formula 3-14 to convert degrees of arc to length.
If the PFAF is in the RF segment, determine its X,Y coordinates using formulas
3-15 and 3-16:
Formula 3-15
X=DFROP+R⋅sin(φ)
Formula 3-16
Y=R− R⋅cos(φ)
6/3/05 8260.52
Par 3.4.2a Page 3-11
Figure 3-3. Determining PFAF Position (X,Y) Relative to LTP
PFAF
LTP FROP
R
R
DFROP
R•Sin(Φ)
R•Cos(Φ)
R•R•Cos(Φ)
Φ
X=D +R•Sin( ) FROP Φ
Y=R-R•Cos(Φ)
3.5 FINAL SEGMENT OEA.
The final segment OEA begins 1×RNP prior to the PFAF and extends to the
LTP/FTP. The OEA contains a sloping OCS to evaluate obstructions prior to DA,
and a visual segment surface from DA to LTP (see figure 3-4).
8260.52 6/3/05
Page 3-12 Par 3.5
Figure 3-4. Final Segment OEA and OCS
2RNP
2RNP
LTP
Glidepath Angle (θ)
ASBL
FAF
LTP DA FAF
Intermediate Segment
OEA
OEA
DVEB
OCSVEB
500’ ROC
The OCS origin distance from LTP (DVEB) and its slope are determined through
application of the Vertical Error Budget (VEB). The VEB calculations require
input of values for two variables: final segment RNP value and temperature (°C)
deviation (ΔISALOW) below the airport ISA temperature. A link to a Microsoft
Excel spread sheet that performs the VEB calculations is available on the
internet at the following address: http://av-info.faa.gov/terps/ under the label
“RNP SAAAR VEB”. See figure 3-2.
Calculate the MSL elevation of the OCS at any distance ‘d’ from RWT using
formula 3-17.
Formula 3-17
VEB
slope
where d = distance along course centerline from RWT
D = distance of OCS origin from LTP
OCS = OCS slope from VEB calculations
VEB
MSL elev
slope
VEB LTP d D
OCS
−
= +
Example
VEB
slope
where d = 4107.23
D = 3559.42
OCS = 20.71
400 410723 3559 42 426 45
2071
. . .
VEBMSL .
−
= + =
LTPelev = 400
6/3/05 8260.52
Par 3.5.1 Page 3-13
3.5.1 Obstacle Evaluation.
If the FAS OCS is not penetrated, the MINIMUM HAT value of 250 ft applies.
Limitation: The distance from LTP to DA must not be less than the
distance from LTP to OCS origin (DVEB). Determine the DA using
formula 3-18.
Formula 3-18
DA = HAT + TDZE
Obstacles that penetrate an OCS may be mitigated by one of the following
actions: remove or lower obstacle, lower the RNP value for the segment (if
appropriate), adjust the lateral path, raise glidepath angle, raise TCH (within
table 3-2 limits), or adjust HAT (see figure 3-5 and formula 3-19).
Figure 3-5. VEB Adjustment of DA or Glidepath Angle
NOTE: DVEB decreases slightly when glidepath angle is increased. Therefore if the
angle is increased to accommodate a penetration, the VEB must be recalculated and
the OCS re-evaluated.
Formula 3-19
( ) ( ) ( )
where = glidepath angle
d = distance (ft) LTP to obstacle
p =
HATadjusted tan d p OCSVEB TCH LTPelev TDZE
θ
= θ ⋅ + ⋅ + + −
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