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tan OCS OCS
adjustment
OCS OCS
p MA VEB
HAT
MA VEB
θ
θ
=
+
Example
( )
OCSslope
OCSslope
18 3 40 2072
1288
40 2027
where p = 18
= 3
VEB = 20.72
MA = 40
tan .
.
HATadjustment .
θ
×
= =
+
Calculate the distance from LTP to DA using formula 4-8.
Formula 4-8
( )
( )
elev
TDZE = Touchdown Zone elevation
LTP = LTP elevation
where = Glidepath angle
tan
FAS adjustment elev
adjustedDA
HAT HAT TCH TDZE LTP
D
θ
θ
+ − + −
=
Example
( )
( )
elev
FAS
300 1288 52 403 400
503498
3
where = Glidepath angle
TCH = 52
TDZE = 403
LTP = 400
HAT = 300
.
.
DadjustedDA tan
θ
+ − + −
= =
HATadjustment = result from formula 4-x
6/3/05 8260.52
Par 4.3.1a Page 4-7
Finally, calculate the adjusted DA value using formula 4-9.
Formula 4-9
DAadjusted=tan(θ)DadjustedDA+(LTPelev + TCH)
Example
( ) ( )
adjustedDA
where = 3 degrees
D = 4977.81
LTPelev = 400
DAadjusted tan 3 4977.81 400 52 712.88
θ
= + + =
TCH = 52
4.3.1 b. Calculating MA climb gradient. See figure 4-4. Where the section 1b OCS
is penetrated and resulting HAT or visibility can be reduced by at least 50 ft or
¼ SM respectively, consider avoiding the obstruction by requiring an MA climb
gradient.
Figure 4-4. MA Climb Gradient
8260.52 6/3/05
Page 4-8 Par 4.3.1b
To determine the climb gradient required to clear a section 1b obstacle, apply
formula 4-10.
Formula 4-10
( )
elev
ab
abobs
where OBS = Obstruction MSL elevation
HMAS = MSL height of HMAS at ab line
D = distance (ft) from ab line to obstacle
8000 elev ab
CG
abobs
Obs HMAS
MA
D
−
=
measured along MA course
Example
( )
elev
ab
abobs
where OBS = 649
HMAS = 457.55
D = 5409
8000 649 45755
28316
5409
.
MACG .
−
= =
If the climb gradient exceeds 425 ft/NM, evaluate the MAS using the OCS slope
appropriate for 425 ft/NM (18.82:1) and adjust DA for the remaining penetration
per paragraph 4.3.1a.
4.3.1 b. (1) Calculating CG termination altitude. Calculate the altitude above
which the climb gradient is no longer required using formula 4-11. Round the
result to the next higher 100 ft increment.
Formula 4-11
( )
CG = climb gradient
Dabobs = distance (ft) from ab line to obstacle
TACG= DA−50 +CG×Dabobs
Example
( )
CG = 284
Dabobs = 5409'
713 50 284 5409 91582 round up to
60 6
10
7
TACG= − + × = . 00
DA = 713
6/3/05 8260.52
Appendix 1
Page 1
APPENDIX 1. VERTICAL ERROR BUDGET (VEB) REQUIRED
OBSTACLE CLEARANCE (ROC) EQUATION EXPLANATION
The required obstacle clearance (ROC) for the VEB is derived by combining known three
standard deviation variations by the root-sum of squares method (RSS) and multiplying by four
thirds to determine a combined four standard deviation ( 4σ ) value. Bias errors are then added
to determine the total ROC.
The sources of variation included in the ROC for the VEB are:
Actual navigation performance error (anpe)
Waypoint precision error (wpr)
Flight technical error (fte) fixed at 75 ft
Altimetry system error (ase)
Vertical angle error (vae)
Automatic terminal information system (atis) fixed at 20 ft
The bias errors for the ROC are:
Body geometry error (bg)
International standard atmosphere temperature deviation (isad)
Semi-span for narrow body fixed at 68
Semi-span for wide body fixed at 131
The ROC equation which combines these is:
4 2 2 2 2 2 2
3
roc=bg−isad+ anpe +wpr +fte +ase +vae +atis
Three Standard Deviation Formulas for Root-Sum of Squares Computations:
The anpe: 1225 1852
03048
. tan
.
anpe= ⋅rnp⋅ ⋅ θ
The wpr: wpr =60⋅tanθ
The fte: fte = 75
The ase: ase = −8.8 ⋅10−8⋅(elev)2 + 6.5 ⋅10−3⋅(elev)+ 50
The vae: (tan tan( 0.01 ))
tan
vae elev ltpelev θ θ
θ
= − − − °
The atis: atis = 20
Bias Error Computations:
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