曝光台 注意防骗
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12.7.2 Since missed approach obstacle clearance is assured only if the missed approach is commenced at the published MAP or above the DA/MDA, the pilot should have preplanned climb out options based on aircraft performance and terrain features. Obstacle clearance is the sole responsibility of the pilot when the approach is continued beyond the MAP.
NOTE.
The FAA Administrator retains the authority to approve instrument approach procedures where the pilot may not necessarily have one of the visual references specified in CFR 14, part 91.175 and related rules. It is not a function of procedure design to ensure compliance with part
91.175. The annotation “Fly Visual to Airport” provides relief from part 91.175 requirements that the pilot have distinctly visible and identifiable visual references prior to descent below MDA/DA.
12.8 Charting of Close in Obstacles on Instru-ment Procedure Charts. Obstacles that are close to the airport may be depicted in either the planview of the instrument approach chart or the airport sketch. Obstacles are charted in only one of the areas, based on space available and distance from the runway. These obstacles could be in the visual segment of the instrument approach procedure. On nonprecision approaches, these obstacles should be considered when determining where to begin descent from the MDA (see “Pilot Operational Considerations When Flying Nonprecision Approaches” in this paragraph).
12.9 Vertical Descent Angle (VDA) on Nonpreci-sion Approaches. FAA policy is to publish VDAs on all nonprecision approaches. Published along with VDA is the threshold crossing height (TCH) that was used to compute the angle. The descent angle may be computed from either the final approach fix (FAF), or a stepdown fix, to the runway threshold at the published TCH. A stepdown fix is only used as the start point when an angle computed from the FAF would place the aircraft below the stepdown fix altitude. The descent angle and TCH information are charted on the profile view of the instrument approach chart following the fix the angle was based on. The optimum descent angle is 3.00 degrees; and whenever possible the approach will be designed using this angle.
12.9.1 The VDA provides the pilot with information not previously available on nonprecision approaches. It provides a means for the pilot to establish a stabilized descent from the FAF or stepdown fix to the MDA. Stabilized descent is a key factor in the reduction of controlled flight into terrain (CFIT) incidents. However, pilots should be aware that the published angle is for information only . it is strictly advisory in nature. There is no implicit additional obstacle protection below the MDA. Pilots must still respect the published minimum descent altitude (MDA) unless the visual cues stated 14 CFR Section 91.175 are present and they can visually
Federal Aviation Administration Twentieth Edition
acquire and avoid obstacles once below the MDA. The presence of a VDA does not guarantee obstacle protection in the visual segment and does not change any of the requirements for flying a nonprecision approach.
12.9.2 Additional protection for the visual segment below the MDA is provided if a VDP is published and descent below the MDA is started at or after the VDP. Protection is also provided, if a Visual Glide Slope Indicator (VGSI); e.g., VASI or PAPI, is installed and the aircraft remains on the VGSI glide path angle from the MDA. In either case, a chart note will indicate if the VDP or VGSI are not coincident with the VDA. On RNAV approach charts, a small shaded arrowhead shaped symbol (see the legend of the U.S. Terminal Procedures books, page H1) from the end of the VDA to the runway indicates that the 34:1 visual surface is clear.
12.9.3 Pilots may use the published angle and estimated/actual groundspeed to find a target rate of descent from the rate of descent table published in the back of the U.S. Terminal Procedures Publication. This rate of descent can be flown with the Vertical Velocity Indicator (VVI) in order to use the VDA as an aid to flying a stabilized descent. No special equipment is required.
12.9.4 Since one of the reasons for publishing a circling only instrument landing procedures is that the descent rate required exceeds the maximum allowed for a straight in approach, circling only procedures may have VDAs which are considerably steeper than the standard 3 degree angle on final. In this case, the VDA provides the crew with information about the descent rate required to land straight in from the FAF or step down fix to the threshold. This is not intended to imply that landing straight ahead is recommended, or even possible, since the descent rate may exceed the capabilities of many aircraft. The pilot must determine how to best maneuver the aircraft within the circling obstacle clearance area in order to land.
12.9.5 In rare cases the LNAV minima may have a lower HAT than minima with a glide path due to the location of the obstacles. This should be a clear indication to the pilot that obstacles exist below the MDA which the pilot must see in order to ensure adequate clearance. In those cases, the glide path may be treated as a VDA and used to descend to the LNAV MDA as long as all the rules for a nonprecision approach are applied at the MDA. However, the pilot must keep in mind the information in this paragraph and in paragraph 12.10.
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