Calculation of PAPI-ILS/Glide Slope
Harmonisation
PAPI ILS-Cross pointer
Other Activities:
Radar and Radio Coverage Calculations
Development of ICAO Flight Profiles
e-mail contact: spichti@yahoo.de
Detailed Calculation of harmonisation between PAPI (Precision Approach
Path Indicator) and ILS- GS (Instrument Landing System- Glide Slope) Signal
1. General:
The requirement to harmonise
the optical glide slope (PAPI) with the electronic glide slope (ILS- GS) is expressed in ICAO
(International Civil Aviation Organisation)- Annex 14 and in the ICAO-
Aerodrome Design Manual, Part 4, Visual Aids.
ICAO prescribes the formula
for calculation of the ILS- GS position as well as for the PAPI position.
Reference point for both calculations is the so called Threshold, which is a
point defined by ICAO. It is located at the beginning of the runway and is
defined by a height above ground of 15m + max. 3m.
The calculation has to take
into account terrain level profile of the longitudinal and the lateral slopes
of the runway and the adjacent terrain accommodating the PAPI and ILS- GS
installations.
The formula for calculation
of the ILS- GS position is to be considered binding for the ICAO- member states
and applies for all categories of aircraft.
The calculation of the PAPI
position is related to the ILS- GS position, but has to take into account a lot
more parameters and interdependencies. Besides the longitudinal and lateral
slope of the runway and the height profile at the PAPI position, the
calculation has to consider the difference in height between the eye level of
the pilot and the ILS antenna, the Minimum Eye Height (MEHT) and the minimum
wheel clearance at the threshold.
The trimming of the aircraft
results in different pitch angles and levels.
The respective
characteristics for eye level, aircraft antenna height and pitch level are
summarised in the Aerodrome Design Manual Part 4.
Frequently the distance
between taxiway outlet and touch down point on the runway and the runway length
are of importance for PAPI positioning, to avoid unnecessary taxiing on the
runway. This is of concern especially in cases where no ILS is available, or
the ILS- GS should be out of service.
Due to the rather global
calculation examples contained in the Aerodrome Design Manual, Part 4, the
requirements for locating the PAPI are reflected rather vague, especially in respect
to harmonisation optimisation.
Various ICAO member states
tend to take the hyperbolic structure of the Glide Slope signal as basis for
the determination of the Threshold crossing height and the respective ILS- GS
position. In such case the GS threshold crossing height has to be calculated
based on the linear glide slope crossing the runway (“Glide Slope Origin”) on a
given GS distance.
2. Background of the ICP Calculation Scheme:
The calculation scheme has
been developed strictly in line with the respective ICAO Regulations.
The prerequisite data are
shown in the schematic layout (Add. 1).
Normally those data can be
depicted from construction plans with height lines (in case of less than 5cm
increments, interpolation is required).
The data depicted from the
plans are entered in the first text page (Add. 2).
The respective Civil Aviation Department (CAD) has to specify/approve the Glide Slope angle, the “ILS-GS Threshold Crossing Height” (hyperbolic or linear), the ILS-GS distance from Threshold, the “most demanding aircraft” and the required “Wheel Clearance”.
These data are then entered
in the respective tables of the calculation scheme, by entering the aircraft
reference data (as listed in the Aerodrome Design Manual. Part 4) in the
formula (Add. 3).
For calculation of the linear
glide slope position in case of a given hyperbolic one, a separate sub- scheme
is available. As a result the relation of runway slope, GS reflection plane
slope, GS Origin, GS distance and threshold height is provided. This
information is also given in graphical form (Add. 4). The GS origin is
the point on the runway where also the PAPI beam has its origin, when projected
on the runway.
Once all data have been entered in the first text page, the calculation automatically calculates the PAPI distance from threshold, the MEHT, the wheel clearance and the harmonisation limits. The results are available for 20’ and 30’ PAPI beam width.
The different pitch levels
provided by ICAO Aerodrome Design Manual, Part 4, are also considered, even
they are of minor impact on the civil aircraft types (Add. 5).
In order to give an impression of the PAPI presentation to an aircraft mix, usually the consideration of B-737, A-300 and B-747 is sufficient. However, any other aircraft type, whose characteristic data are available can be considered.
By inserting different PAPI
distances into the calculation, the impact on landing length or distance to the
taxiway outlet(s) is available.
For visualisation the
calculation results are also presented in graphical form (Add. 6).
The advantage of the calculation scheme is the quick consideration of changing customer demands without redoing complete manual calculations.
For calculation of the PAPI
position on sloping terrain, the longitudinal slope is automatically included
in the calculation.
Once the cross slope within
the considered PAPI area is available, the pole height of the PAPI can be
selected by varying the PAPI beam level related to the runway level at the PAPI
position (Add. 7).
3. Summary:
The ICP calculation scheme is
considered to be a valuable tool for investigating the influence of PAPI
positioning related to the ILS-GS, based on varying customer demands. The
calculation is strictly in line with the ICAO regulations and the results can
be used for optimising the PAPI position for individual airports and their
related requirements.
Various calculation results
can be combined in a summary table, showing the interdependencies of i.e.
distance, MEHT/wheel clearance, TCH (threshold crossing height)and touch-down
distance, based on changing one or more selected parameters.
The considered parameters
are:
ILS- GS distance from
threshold
ILS-GS threshold crossing
height
ILS-GS glide angle
ILS-GS «Origin» on the runway
Runway longitudinal slope
Longitudinal terrain slope at
ILS-GS and PAPI locations
PAPI distance from threshold
related to ILS-GS origin
Lateral slope at ILS-GS location
related to the runway
Lateral PAPI slope(s) related
to the runway
Aircraft parameters according
to ICAO Aerodrome Design Manual, Part 4
Ideal PAPI position related
to the reference aircraft
PAPI position matched to MEHT
and wheel clearance 6m and 9m for different eye levels
Wheel clearance for 20 ‘ and
30’ PAPI beam width for different aircraft
Distance limit for
harmonisation related to threshold for various aircraft
4. List of Addenda:
Addendum 1:
Layout schematic for data acquisition
Addendum 2:
First Text Page for data insertion
Addendum 3:
ICAO data for various aircraft types
Addendum 4:
Relation between runway and glide slope origin
Addendum 5:
Influence of pitch level on the PAPI distance and MEHT
Addendum 6:
Examples of visualisation
Addendum 7:
PAPI- position related to the runway
Addendum 1:
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Abbreviations: |
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D = Longitudinal distance |
ey = Eye |
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d = cross distance |
ant = ILS antenna |
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H = Ground level |
rad = Wheel |
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h = Height above ground |
PAPI = papi = Precision
Approach Path Indicator |
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q = Glide
Path Angle |
RWY = rwy = Runway |
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trh = Runway Threshold |
CL = Centre Line |
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xh = Threshold Crossing Height |
Whcl= Wheel Clearance |
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GP = gp = Glide
Path/Slope |
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@ = Longitudinal
Slope |
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Expected Area of
Installation = Area which has: |
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- almost no longitudinal
slope changes |
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- to be enlarged if
required by calculation results |
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