Safety around airports is maintained through regulations set by the International Civil Aviation Organization (ICAO). Standards define Obstacle Clearance Limits (OCLs) for operational areas; objects penetrating these areas violate safety. The standards take into account generic operational procedures, but actual OCL implementation depends on the physical layout of the airport. It is thus essential to map and visualise restricted zones and objects that could interfere with aeronautical activity.

Kleia’at Airport

Kleia’at is one of three active airports in Lebanon. It lies on the Mediterranean coast, some 90km from Beirut and about 7km from the northern Lebanese border with Syria. It has two opposite runways, named 06 and 24. The reference point of the airport is taken to be the midpoint of the runway at latitude N34^o 35.139’, longitude E36^o 00.183’ and mean elevation 7m above sea level. The airport is currently a military airbase also catering for some general aviation and training traffic. Recent government plans to transform it into a regional civilian airport have prompted the need to obtain accurate 3D aerial zoning to define its obstacle limiting surfaces.

Zoning Specifications

The development of the application required first specification of reference codes given in Annex 14 to the Convention on International Civil Aviation; these codes define runway dimensions The coding of runway type also needed to be fixed because of its direct bearing on the geometry of the OCLs. Since the runway at Kleia’at is 2,850m long and 48m in width, the airport was coded ‘4D’; the numeral ‘4’ indicates that the runway is longer than 1,800m, while ‘D’ indicates that it is wider than 36m but less than 52m. Kleia’at is currently a non-instrument approach airport. However, future plans are to transform it into a CAT I precision-approach airport. Runway specifications differ regarding surface dimensions for approach and departure. The surface dimensions for the 4D-CAT I approach runways as defined in Annex 14 are given in Table 1, and for take-off climb in Table 2. Both runways are to be used for departure.

Mapping Reality

To achieve the 3D-model defining the OCLs around Kleia’at air­­port, a three-step methodology was adopted. The first step involved accurate definition of the phy­sical characteristics of the airport. Ortho-rectified satellite  imageryof 1m reso­­lution was used to define paved areas of the airport such as runways, taxiways, aprons and intersections, to identify airport buildings and facilities and to locate essential features such as start and end of runways, runway centreline and reference point. Elevation contours were digitised from 1:20,000 maps. Although more accurate data sources could have been used, such as as-built airport drawings, satellite images are adequate to illustrate the procedure.

Design of 2D-Model

The next step involved the design of a 2D-model outlining extent of the OCL, including conical, inner horizontal, approach surfaces, departure surfaces and transition surface. The starting point was to define the runway zone: a rectangular feature comprising 150m on either side of the runway centreline and extending 60m from each threshold. The approaches relative to each runway, both in terms of longitudinal distance from each end of the runway zone and of the lateral angular expanse, were fixed according to the definitions in Table 1. The same procedure was applied to the departure areas. In both cases, limits in length direction extended to 15km from the narrower edge of the runway zone. The circles encompassing the inner horizontal and conical surfaces were also included; these were centred at the reference point, with respect­ive radii of 4km and 6km.

From 2D to 3D

Once ready, the OCLs 2D-model was extended to 3D by introducing appropriate heights and slopes, taking into account terrain heights and fixing elevations of the various points defining these surfaces (Figure 4). In particular, the airport reference point was set at 7m above sea level, while the edges of the runway zone on either side of the thres­holds were set at 5m and 13m. The elevations of the boundaries of the various sections of the approach and departure clearance surfaces were also appropriately set. As required by the definitions outlined in Table 1, the upper level of the transition zone was made to intersect with both the departure surfaces and the inner horizontal surface at 45m above the reference point. Around the latter OCL, the conical surface projected upwards to 100m at a rate of 5%.

Results

The GIS-model enabled clear assessment of the geometry of the OCLs at Kleia’at airport. Maximum permitted height of obs­tacles such as buildings and cables could be determined with relative ease and good accuracy as a function of their distance from the airport and height above sea level. The GIS-model also enabled identification of municipalities subject to zoning restrictions (Figure 5, top left). The airport authority and the Civil Aviation Authority have to work together with municipal­ities to ensure that aerial zoning criteria are respected. The airport conical surface and parts of the Departure 06 and Approach 24 surfaces extend beyond the border with Syria, so that the design of departure and approach procedures for these runways requires bilateral dialogue. Figure 5, top right, shows a 3D-view of the approach, departure and transition surfaces for north-easterly Lebanese terrain. Such a GIS representation enables acquisition of the difference between the terrain and limiting surface elevations, and the subsequent deduction of obstacle height limits at any location. Similar representations could be generated for the inner horizontal and conical surfaces. The two images at the bottom of Figure 5 illustrate a simulation in which buildings in the town to the north-east of the airport were extruded 10.5m above ground level. Some such height buildings would have intruded in the OCL and will need on-ground assessment.

Concluding Remarks

It is essential that this GIS application be applied at other Lebanese airports and that these are regularly updated to meet with new ICAO requirements. Moreover, the work should be extended to incorporate existing obstacles to ensure that they meet the standards, and be used as a decision-support system for building future constructions. The developed GIS can easily be used as a tool for managing airport facilities, pavements and civil works.

Acknowledgements

Thanks are due to the Lebanese Air Force Command and cadet officers, Mrs Amal Iaaly-Sankari, University of Balamand, and students there.

Further Reading

• Annex 14 to the Convention on International Civil Aviation, International Standards and Recommended Practices, Aero­dromes, Vol. I: Aerodrome Design and Operations, International Civil Aviation Organization, Second Edition, July 1995.

• Arafa, M. R., Zanaty, A.A., Hasan, L.M., 2005, Airport Management and Development System, Paper No. 2259, 25th ESRI International User Conference, San Diego, CA, USA, July 25-29, 2005.

• Iza, S., 2004, Birdstrike Data with ArcView at Santa Barbara Airport”, Paper No. 1178, 24th ESRI International User Conference, San Diego, CA, USA, August 9–13, 2004.

• Jadayel, O.C. and Ibrahim, R.Y., 2006, Three Dimensional Aerial Zoning around a Lebanese Airport, Paper No. 1270, 26th ESRI International User Conference, San Diego, CA, USA, August 7-11, 2006.