Visual Segment Surface (VSS)

28.10.2011

Submission:

I have a little question regarding the Visual Segment Surface (VSS). According to PANS-OPS, objects up to 15m height as well as moving objects such as aircraft may penetrate the VSS. This seems a little weird, especially when thinking about ICAO Annex 14. The 15m exception can be justified, at least as long you have a RDH of 15m, but what about the holding aircraft? Within Annex 14, such objects shall not penetrate the approach surface. Therefore, there shall be no holding position leading to aircraft penetrating the approach surface. In the plan view, the VSS and Annex 14 Approach Surface are the same (at least near the runway). However, the Annex 14 Approach Surface is lower than the VSS. Therefore, it should be possible, that an aircraft is penetrating the VSS. So, why is this exception included in PANS-OPS? What is the rationale?

Peter P. Germany

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Answer or Commentary:

The VSS is mainly there for one reason: When the aircraft hits the OCH it is possible that the controlling obstacle that resulted in the OCH is still ahead. When descending below OCH it could now be that there is an encounter with the controlling obstacle if the VSS was not assessed. That is why aircraft on ground are not part of that equation. If the Annex 14 obstacle limitation process is correctly applied, aircraft will never penetrate the VSS. As you say, the Annex 14 app surface is LOWER, therefore more conservative. If the Annex 14 is not penetrated, the VSS will not be either.

Beat Zimmermann - Chairman of the IFPP - Air Navigation Institute GmbH - Switzerland


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