The term Alighting Area (ICAO), abbreviated as ALA, is a specific zone defined in aviation operations to facilitate the safe touchdown and deceleration of aircraft during landing phases. According to the International Civil Aviation Organization (ICAO), an Alighting Area refers to a designated portion of the aerodrome surface prepared to receive an aircraft in the landing phase, ensuring controlled and safe operations. The concept and specifications for the Alighting Area are crucial for airport design, operational efficiency, and compliance with international aviation standards.
The ICAO’s guidelines for the Alighting Area are extensively outlined in Annex 14 to the Convention on International Civil Aviation, Volume I – Aerodrome Design and Operations. The precise definition and parameters enable airports worldwide to maintain standardization in runway design, which is vital for safety, particularly in complex or congested environments. This article explores the technical aspects, requirements, and implications of the Alighting Area (ICAO) in aviation.
Understanding the Alighting Area (ICAO)
The Alighting Area (ICAO) is essentially the portion of an aerodrome surface—usually runway terrain—prepared and intended for aircraft to complete the final landing maneuvers. It covers the specific zone where the aircraft initially makes contact with the ground, allowing it to decelerate safely before reaching taxiways or other parts of the airport. This area must be adequately designed to withstand the loads exerted by landing aircraft and to ensure traction, drainage, and minimal foreign object debris.
ICAO stipulates that the Alighting Area must be free of obstacles, maintain specific surface characteristics, and meet particular dimensional standards depending on critical aircraft characteristics that will use the aerodrome. These dimensions are based on criteria such as aircraft wingspan, approach speed, and landing weight. For reference, runways involving large jets like Boeing 777 or Airbus A380 require longer and more robust alighting areas, often exceeding 2,500 meters in length and 45 meters in width, with shoulders extending even wider.
Technical Specifications and Design Criteria of Alighting Area (ICAO)
The Alighting Area (ICAO) must comply with several technical regulations related to runway strength, surface friction, and markings. The pavement must sustain the maximum taxying weight and landing impact. ICAO Annex 14 specifies that runway pavements should be evaluated using the Pavement Classification Number (PCN) system, which communicates the pavement’s bearing capacity to accommodate aircraft with various Aircraft Classification Numbers (ACN).
Additionally, surface materials in the Alighting Area need to provide a friction coefficient to handle aircraft braking measures safely. Friction values often hover around 0.3 to 0.4 under wet conditions for good performance. Moreover, the Alighting Area’s slope and grade are carefully engineered. ICAO recommends that longitudinal slope should generally not exceed 1.25%, with a transversal slope allowing effective drainage, usually around 1.5% to 2.0%.
Safety and Operational Implications of Alighting Area (ICAO)
Proper implementation of the Alighting Area (ICAO) ensures that aircraft land safely without risk of skidding, runway excursions, or structural failure of the remaining runway. Safety margins are critical, including provisions for runway end safety areas (RESAs) adjacent to the Alighting Area to provide an additional margin during aborted landings or overruns. The ICAO recommends a RESA length of at least 90 meters beyond the runway threshold or strip.