UFC 3-535-01
17 November 2005
Figure 12-6. Siting PAPI without an ILS Glide Slope (2 of 2)
c. Case 4 - Runway with varying grade.
Ideal
ath, θ
RRP
ide p
Gl
RRP
TCH
H
Horizontal reference plane
H
1
0
h
RW surface
1
d
1
Use this method if longitudinal runway grade changes within 671 meters (2200 feet) from the runway threshold.
Consider that a 0.1% change in runway grade at about 150M (500') from threshold translates to a 15cm (6") change in
elevation at 300M (1,000'), and about a 3M (10') error in calculating the RRP, using the runway grade beginning at the
threshold. The trial method requires elevation data along the runway centerline in proximity of the PAPI site.
(1) Select a trial value for d ("d "). [Case 1 or Case 2 can be used to select initial trial value].
1
(2) At distance d , determine elevation difference from threshold (H - H = h )
0
1
1
1
TCH + h
=? tan θ
(3) Test d and h in following equation:
1
d
1
1
1
0
[NOTE: tan θ = 0.0524 for glide path angle of 3 .]
(4) If value in (3) is larger than tan θ , then increase d, determine new h, and test equation in (3). If value
is smaller than tan θ , then decrease d, determine new h, and test equation in (3). Continue until within
about + .0001 of tan θ [this yields a value for "d" within about + 2' of where RRP should be located.
Example data from field survey
EXAMPLE Case 4 (Assume the following: TCH = 50', θ = 3 ).
o
d
Point Station
H
h
110.4'
0
-
Thld, 0 0+00
At d = 950', h = 4.2', and (TCH+h)/d = 0.0571 (too large)
950'
4.2'
114.6'
9+50
1
1
1
1,00'
4.6'
115.0'
10+00
2
At d = 1,000', h = 4.6', and (TCH+h)/d = 0.0546 (closer)
1,050'
5.0'
115.4'
10+50
3
2
2
At d = 1,050', h = 5.0', and (TCH+h)/d = 0.0524 (matches tan θ - OK)
3
3
[NOTE: Suggested longitudinal tolerance for locating PAPI is + or - 10 `.]
DEFINITIONS:
RRP =
RW reference point, where PAPI is located based on adjustment for runway grade.
Ideal RRP = RW reference point if runway has 0% grade (no slope).
RW =
Runway
TCH =
Threshold crossing height
d=
Distance PAPI is located from runway threshold, based on adjustment for runway grade.
θ=
Glide path angle, degrees (from horizontal).
α=
Runway slope, degrees (use positive value in above equations).
h=
Elevation (height) difference between RW threshold and RRP, measured on RW centerline surface.
H=
Elevation at a point along runway centerline.
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