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时间:2011-04-18 01:03来源:蓝天飞行翻译 作者:航空
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24.3.4.2 The required visual references for the runway of intended landing are no longer distinctly visible and identifiable to the pilot using the EFVS imagery;
24.3.4.3 The aircraft is not continuously in a position from which a descent to a landing can be made on the intended runway, at a normal rate of descent, using normal maneuvers; or
24.3.4.4 For operations under 14 CFR parts 121 and 135, the descent rate of the aircraft would not allow touchdown to occur within the TDZ of the runway of intended landing.
24.3.5 Missed Approach Considerations. It should be noted that a missed approach after passing the DA, or beyond the missed approach point (MAP), involves additional risk until established on the published missed approach segment. Initiating a go.around after passing the published MAP may result in loss of obstacle clearance. As with any approach, pilot planning should include contingen-cies between the published MAP and touchdown with reference to obstacle clearance, aircraft performance, and alternate escape plans.
24.4 EFVS Operations At and Below 100 Feet Above the TDZE. At and below 100 feet above the TDZE, the regulations do not require the EFVS to be turned off or the display to be stowed in order to continue to a landing. A pilot may continue the approach below this altitude using an EFVS as long as the required visual references can be seen through the display using natural vision. An operator may not continue to descend beyond this point by relying solely on the sensor image displayed on the EFVS.
24.4.1 Required Visual References. In order to descend below 100 feet above the TDZE, the flight visibility..assessed using natural vision..must be sufficient for the following visual references to be distinctly visible and identifiable to the pilot without reliance on the EFVS to continue to a landing:
24.4.1.1 The lights or markings of the threshold, or
24.4.1.2 The lights or markings of the TDZ.
It is important to note that from 100 feet above the TDZE and below, the flight visibility does not have to be equal to or greater than the visibility prescribed for the IAP in order to continue descending. It only has to be sufficient for the visual references required by 14 CFR part 91.175 (l)(4) to be distinctly visible and identifiable to the pilot without reliance on the EFVS.
24.4.2 Comparison of Visual Reference Require-ments for EFVS and Natural Vision. Again, the visual reference requirements for EFVS in 14 CFR part 91.175 (l)(4) are more stringent than those required for natural vision in 14 CFR part 91.175 (c)(3). The main differences for EFVS operations are that the ALS and red terminating bars or red side row bars, the REIL, and the VASI cannot be used as visual references. Only very specific visual references from the threshold or the TDZ can be used (that is, the lights or markings of the threshold or the lights or markings of the TDZ).
24.4.3 When to Go Around. A missed approach must be initiated when the pilot determines that:
24.4.3.1 The flight visibility is no longer sufficient to distinctly see and identify the required visual references listed in 14 CFR part 91.175 (l)(4) using natural vision;
24.4.3.2 The aircraft is not continuously in a position from which a descent to a landing can be made on the intended runway, at a normal rate of descent, using normal maneuvers; or

Federal Aviation Administration Twentieth Edition
24.4.3.3 For operations under 14 CFR parts 121 and 135, the descent rate of the aircraft would not allow touchdown to occur within the TDZ of the runway of intended landing.
24.4.4 While touchdown within the TDZ is not specifically addressed in the regulations for operators other than 14 CFR parts 121 and 135 operators, continued operations below DA or MDA where touchdown in the TDZ is not assured, where a high sink rate occurs, or where the decision to conduct a missed approach procedure is not executed in a timely manner, all create a significant risk to the operation.
24.4.5 Missed Approach Considerations. As noted earlier, a missed approach initiated after the DA or MAP involves additional risk. At 100 feet or less above the runway, it is likely that an aircraft is significantly below the TERPS missed approach obstacle clearance surface. Prior planning is recommended and should include contingencies between the published MAP and touchdown with reference to obstacle clearance, aircraft performance, and alternate escape plans.
24.4.6
Light Emitting Diode (LED) Airport Lighting Impact on EFVS Operations. The FAA has recently begun to replace incandescent lamps with LEDs at some airports in threshold lights, taxiway edge lights, taxiway centerline lights, low intensity runway edge lights, windcone lights, beacons, and some obstruction lighting. Pilots should be aware that LED lights cannot be sensed by current EFVS systems.

25.
Visual Approach


25.1 A visual approach is conducted on an IFR flight plan and authorizes a pilot to proceed visually and clear of clouds to the airport. The pilot must have either the airport or the preceding identified aircraft in sight. This approach must be authorized and controlled by the appropriate air traffic control facility. Reported weather at the airport must have a ceiling at or above 1,000 feet and visibility 3 miles or greater. ATC may authorize this type approach when it will be operationally beneficial. Visual approaches are an IFR procedure conducted under Instrument Flight Rules in visual meteorological conditions. Cloud clearance requirements of 14 CFR Sec-tion 91.155 are not applicable, unless required by operation specifications.
 
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