Safety Assessment for reduced Approach Lighting System

In some cases, the required length for an Approach Lighting System cannot be fully provided in accordance to ICAO or EASA requirements: due to topographical (lake, sea, mountain) or other reasons, only a reduced Approach Lighting System can be provided.

Such deviation may hinder airport operators to introduce precision approaches (e.g. ILS CAT I, ILS CAT II), or may require the introduction of operational restrictions. However, an Aeronautical Study or Safety Assessment may be used to determine if the safety of air operations is effectively compromised, and if the non-compliant Approach Lighting System can be tolerated.

A European airport operator was confronted with the above-detailed situation: the required 900m length for the Approach Lighting System could not be provided to the full extent for ILS CAT I and CAT II operations. It commissioned airsight to conduct a safety assessment aiming to evaluate the impact of the non-compliant installation on the safety of air operations.

airsight's assessment consisted first in a comprehensive review of the applicable requirements, contained in different documents, such as ICAO Annex 14 – Volume 1 and EASA.CS.ADR and associated Guidance Material (GM), but also in EASA “Commercial Air Transportation” (Part-CAT) and “Specific approvals” (Part-SPA).

Several scenarios were subsequently modelled, based on the possible combinations resulting from different lengths of an approach lighting system with respect of the visual reference reaching decision altitude / decision height (DH) for CAT I and planned CAT II operations. Each scenario were modelled and assessed by a group of multi-disciplinary experts (commercial pilots, air traffic controllers, aviation safety expert, etc.) taking into account all relevant operational parameters (aircraft types, visibility conditions, approach type, etc.).

The present safety assessment results could demonstrate that a reduced approach lighting systems length, combined with risk mitigating measures, is acceptable in terms of safety according to the As Low as Reasonably Practicable (ALARP) principles.