Aeronautical Study of Visual Segment Surface (VSS) obstacle penetrations: Taiwan

Surfaces established by Procedure designers of Air Navigation Services and Aircraft Operations (PANSOPS) are intended to safeguard an aeroplane from collision with obstacles when flying on instruments. The VSS is designed to keep the area from where an aircraft reaches decision altitude or minimum descent altitude (depending on the approach type), to the landing threshold on a straight-in approach, clear of obstacles. Per ICAO Doc 8169 Vol II, if the VSS is penetrated, the approach procedure should not be promulgated without an aeronautical study.

In order to obtain insights into the potential operational impacts of the identified obstacles penetrating the VSS, MovingDot held two group interview sessions with safety management representatives and pilots respectively. If based on provided information areas of concern would have been identified, an incident assessment initiative would be warranted. A third group interview session was with obstacle monitoring representatives, providing insight into the processes in place for regular obstacle verification and identification of potential new obstacles with corresponding corrective and/or communication efforts. If based on provided information areas of concern would have been identified, a full obstacle verification initiative would be warranted.

VSS obstacle penetrations that were also found to penetrate the more stringent obstacle clearance surface (OCS) require further analysis beyond a VSS Aeronautical Study if the obstacle cannot be removed or modified to no longer penetrate the OCS, or if cancellation of the flight procedure is undesirable.

The aeronautical study was performed based on the VSS Assessments performed by ANI Service GmbH and the therein identified VSS penetrating obstacles.

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Nienke Jester

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