O que é uma superfície de identificação de obstáculos e por que um piloto a penetraria intencionalmente durante uma abordagem de ILS?

As superfícies de identificação de obstáculos se aplicam às partidas e à parte de um IAP de precisão além do ponto de descida visual. Se você estiver nas nuvens, nunca deve penetrar no OIS na partida.

Na chegada, o VDP garante a remoção de obstáculos com uma abordagem normal ao pouso. As abordagens apenas do ILS não têm um VDP representado, portanto não há OIS para penetrar. (A inclinação de deslizamento leva você diretamente à zona de aterrissagem.) As abordagens ILS / LOC (e somente Localizer) possuem um VDP para a versão não precisa da abordagem. Você pode penetrar no OIC em uma abordagem localizadora e, se isso acontecer, os mínimos de visibilidade serão aumentados conforme explicado no último parágrafo do AIM abaixo.

O projeto de aeroporto AC 150-5300-13-c12 tem uma boa visualização da partida do OIC. (Como um aparte, ele tem muitos quadros e gráficos mostrando como as partidas e abordagens são projetadas.)

AIM 5-2-8. Procedimentos de partida de instrumentos (DP) - Procedimentos de partida de obstáculos (ODP) e partidas padrão de instrumentos (SID)

…if an obstacle penetrates what is called the 40:1 obstacle identification surface, then the procedure designer chooses whether to:

1. Establish a steeper than normal climb gradient; or

2. Establish a steeper than normal climb gradient with an alternative that increases takeoff minima to allow the pilot to visually remain clear of the obstacle( s); or

3. Design and publish a specific departure route; or

4. A combination or all of the above.

5. The 40:1 obstacle identification surface (OIS) begins at the departure end of runway (DER) and slopes upward at 152 FPNM until reaching the minimum IFR altitude or entering the en route structure. This assessment area is limited to 25 NM from the airport in nonmountainous areas and 46 NM in designated mountainous areas. Beyond this distance, the pilot is responsible for obstacle clearance if not operating on a published route, if below (having not reached) the MEA or MOCA of a published route, or an ATC assigned altitude. See FIG 5−2−1. (Ref 14 CFR 91.177 for further information on en route altitudes.)

5-4-5. Gráficos do procedimento de abordagem por instrumento (IAP)

h. The Visual Descent Point (VDP), identified by the symbol (V), is a defined point on the final approach course of a nonprecision straight−in approach procedure from which a stabilized visual descent from the MDA to the runway touchdown point may be commenced. The pilot should not descend below the MDA prior to reaching the VDP.

i. A visual segment obstruction evaluation is accomplished during procedure design on all IAPs. Obstacles (both lighted and unlighted) are allowed to penetrate the visual segment obstacle identification surfaces. Identified obstacle penetrations may cause restrictions to instrument approach operations which may include an increased approach visibility requirement, not publishing a VDP, and/or prohibiting night instrument operations to the runway. There is no implicit obstacle protection from the MDA/DA to the touchdown point. Accordingly, it is the responsibility of the pilot to visually acquire and avoid obstacles below the MDA/DA during transition to landing.

Editar: Este objetivo é consistente com o que o Manual de Procedimentos do Instrumento diz sobre abordagens de não precisão, mas não é consistente com o que o manual diz sobre o potencial de obstáculos nas abordagens de ILS.

p 7-9

...if an ILS is configured with approach lights or a nonprecision approach is configured with either MALSR, SSALR,or ALSF-1 lighting configurations and the procedure has a published visibility of 3/4 SM or greater, a penetration of the final approach OIS may exist. Also, pilots will be unable to determine whether there are penetrations of the final approach OIS if a nonprecision procedure does not have approach lights, or is configured with ODALS,MALS, or SSALS/SALS lighting since the minimum published visibility will be 3/4SM or greater.

As a rule of thumb, approaches with published visibilities of 3/4SM or more should be regarded as having final approach OIS penetrations and care must be taken to avoid any obstacles in the visual segment. Approaches with published visibilities of 1/2 SM or less are free of OIS penetrations...