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The issue was given to a multidisciplined group called the Airport Obstructions Standards Committee (AOSC) to resolve. After much deliberation, this group grandfathered runways and taxiways meeting existing separation standards into the airport design standards and determined further analysis was neces- sary. In the interim, separation standards for construction of new runways or taxiways were increased to 500 ft for Cat II/III operations involving Group V aircraft and for Cat I approaches involving Group VI aircraft. For Group VI aircraft making a Cat II/III approach, a separation of 550 ft would be required between new runways and taxiways. The AOSC work is docu- mented in AOSC Decision Document #04 (AOSC, 2005). ICAO Rationale To harmonize the development of aviation (including air- ports) globally, the ICAO was established toward the end of World War II with the signing of the Convention on Interna- tional Civil Aviation (also known as the Chicago Convention) on December 7, 1944. Since then, ICAO has developed and updated international speciï¬cations on all aspects of aviation. In Annex 14 to the Chicago Convention, ï¬rst published in 1949, the ICAO promulgated speciï¬cations on airport design and operations (ICAO, 1949). ICAO has kept pace with technological developments in the aircraft industry and kept Annex 14 current to provide to its Contracting States (or Member Nations) the minimum safety speciï¬cations for designing new airports and upgrading exist- ing ones to handle succeeding generations of newer, larger, and heavier aircraft. Many of the current standards and recommended practices (SARPs) contained in Chapter 3 of Annex 14 were deï¬ned by the Aerodrome Reference Code Panel (ARCP) in 1981 (ICAO, 1981). As part of the process to deï¬ne a new reference code for airports, ARCP also undertook a fundamental review of SARPs based on a more rational approach. In 1990, Annex 14 was separated into two volumes (ICAO, 1990). Volume I now contains international speciï¬cations on aerodrome design and operations only, and Volume II deals with the design of heliports. Statistics have shown that approach and landing is the most critical phase of a ï¬ight because the aircraft must follow a pre- cise and stable approach path despite the challenging circum- stances that characterize this flight phaseâaircraft engine power is at its minimum, weather conditions on the ground may pose difï¬culties for landing, and habitation and land devel- opments surrounding airports can be signiï¬cantly impacted by deviations from the approach path. Moreover, aircraft may sometimes touchdown before the runway arrival end or reject the takeoff and depart the runway if something goes wrong. These are the main reasons runways have a safety area. The FAA refers to this area as an RSA, whereas the ICAO deï¬nes an area with an equivalent function, con- sisting of the runway strip plus the runway end safety area (RESA). The objective of this area is to reduce the risk of dam- age to aircraft running off a runway and protect aircraft ï¬ying over a runway during takeoff or landing operations. The safety area applies not only to the airspace on or around an airport but also to the ground itself. Runway Strip Width ARCPâs basis for the speciï¬cations of the graded portion of the strip is the acceptable risk of occurrence of aircraft veer- offs. From the information available, there seems to be no deï¬ned basis for the development of the speciï¬cation of the full strip width for the protection of over-ï¬ying aircraft using the CRM. ARCP identiï¬ed the following factors in the deï¬nition of the strip width: ⢠Aircraft approach speed ⢠Wingspan ⢠Aircraft mass ⢠Type of approach (visual or instrument) Statistical data on aircraft veer-off events presented at the 8th Air Navigation Conference in 1974 were the basis for the 8 Figure 4. Wingtip clearance for taxilanes.
analysis. The frequency of veer-offs exceeding a given dis- tance from the runway centerline were determined according to the type of operation and class of aircraft. To maintain a safety area around the runway, a runway strip width of 984 ft (300 m) is specified for instrument runways, and a runway strip of 492 ft (150 m) is speci- fied for smaller, non-instrument runways. The strip is symmetrically located on either side of the runway center- line. The central portion is required to be graded to certain specified slopes so that it is less likely that an aircraft will suffer substantial damage during runway veer-offs. These requirements are used to establish a safety area around the runway in which only those objects that must be located there are permitted, subject to the applicable frangibility criteria being met. Airfield Separations Every aircraft landing or taking off on a runway must pro- ceed along a system of taxiways. During these movements, aircraft should be protected by wide, obstacle-free areas; thus, even the circulation areas (taxiways and aprons) must be located at suitable distances apart and at a speciï¬ed distance from the runway. The early speciï¬cations in ICAO Annex 14 were based on the layouts of airï¬elds that existed at the timeâmostly military airï¬eldsâthat were deemed to be examples of best practice. It is not uncommon to see older airports with runways from 98 to 197 ft (30 to 60 m) wide. Similarly, the circulation taxiways were separated from the runways so that aircraft on the taxi- way did not cause major risk to aircraft landing or taking off from the runway. Since then, numerous ICAO studies, undertaken with assis- tance from ICAO technical panels and study groups, have ï¬ne- tuned the speciï¬cations as actual aircraft performance results and airport experience have become available. Improvements in aircraft manufacturing technology, better training, and the availability of modern visual aids have also contributed to this ï¬ne-tuning. The broad principles governing airfield separations are explained in greater detail in the following sections. Separation Distance between a Runway and a Taxiway A parallel taxiway is located such that no part of the largest aircraft expected to operate on the parallel taxiway would penetrate into the adjacent runway strip. This is intended to accommodate any potential veer-off of a landing aircraft when the taxiway is being used and also to provide a sterile area, free of obstacles that may endanger an aircraft executing a missed approach or balked landing maneuver. The separation distance is expressed as follows: where SRWY-TWY is the distance between the centerlines of a runway and a parallel taxiway, SW is the runway strip width, and WS is the aircraft wingspan. Figure 5 depicts the main factors in the ICAO rationale. Although a link taxiway for entry into and exit from the runway is located within the runway strip, whenever the runway is in use, an aircraft on a link taxiway is required to stop and hold at a distance of 295 ft (90 m) from the run- way centerline (ICAO Code E) (ICAO, 2004). For aircraft designated ICAO Code F, where the wingspan is greater than 213 ft (65 m) but not more than 262 ft (80 m), the holding position location is at a distance of 350 ft (107 m) from the runway centerline (ICAO, 2004). This distance may need to be increased for certain operational conditions, and this minimum holding distance should be reviewed if it interferes with radio navigational aids provided for the runway. The separation distances between a runway and ï¬xed objects other than visual aids required for air navigation purposes are the following (ICAO, 2006a): ⢠Within 254 ft (77.5 m) of the runway center line of a pre- cision approach runway Cat I, II, or III where the code number is 3 or 4 and the code letter is F; S SW WS RWY-TWY = + 2 2 9 Figure 5. Runway/parallel taxiway separation distance.