FAA关于RVR的概念
跑道视程概念
运行最低标准用地面能见度、塔台能见度、跑道能见度值和跑道视程等术语来规定。像跑道视程这样的系统迅速而可靠地提供飞行员预期在接地区和跑道沿线会碰到的目视条件报告。
A用校准的视距测量仪系统及找出周边背景灯效果和跑道灯强度的办法来测量跑道测程。策略地设置视距测量仪表系统以提供有关一条跑道的三个基本段中的一个或更多的跑道视程测量。这三个基本段是：接地区(TDZ)、跑道中段(MID)和跑道末端(Rollout).
(1)跑道视程是用仪表得到的数值，该数值反映在跑道上或邻近跑道段的人造目视条件。这种人造目视条件靠使用高强度跑道边界、接地区和中心线等灯光来实现。这些灯光增加了着陆道面的醒目度并“伸向”飞行员，从而产生一个明显好于地面能见度或塔台能见度报告的目视条件。由于跑道视程以使用高强度灯光为基础，在任何特种浓雾下，跑道视程 将明显大于报告的能见度。既然跑道视程是基于高强度灯光，跑道视程报告只有在与获得报告那一段跑道(接地区、跑道中段或跑道末端)或接近该跑道的目视条件相结合才有意义。除非飞行员也看到作为报告基础的高强度灯光，否则，跑道视程报告没有意义。
(2)为了正确运用运行最低标准，理解跑道视程至关重要。下面是“什么是跑道视程”的陈述条目：
•跑道视程是用仪器得到的数值。
•跑道视程是用设置在距跑道中心线约400英尺的视距测量仪实时测量的。
•跑道视程与大气的透射度(暗度)有关。
•跑道视程是当航空器在或稍高于与报告有关的跑道段时飞行员应看见距离的近似值。
•跑道视程是参考跑道灯光和物体对比进行校准的。
•跑道视程是一个随跑道灯光设定而变化的数值。
•跑道视程是只对与跑道视程报告有关的跑道段(接地区、跑道中段或跑道末端)有意义的数值。
(3)下面是“什么不是跑道视程”的陈述条目：
•跑道视程不是气象能见度的量度。
•跑道视程不是地面能见度或塔台能见度的量度。
•跑道视程不是滑行道、客机坪、停机坪上目视条件的量度。
•跑道视程不是在或接近最低下降高度或决断高时目视条件的量度。
•跑道视程不是由观测员肉眼所观测或报告的。
•跑道视程不是“能见度”。
注：跑道视程数值在夜间可比地面能见度或塔台能见度大5至6倍、在白天大2至3倍。
CONCEPT OF RVR. Operating minimums are specified in terms of ground visibility, tower visibility, runway visibility values (RVV), and runway visual range (RVR). The RVR concept has evolved over a long period and its use in the U.S. began in 1955. As operating minimums were reduced due to improvements in airborne and ground based equipment, it became more likely that pilots would not see the full length of the runway upon arrival at the specified decision point. Positions established for taking visibility observations were often several miles from the approach end of many runways. This resulted in reported visibility values which frequently did not represent the seeing conditions encountered during the final stages of approach and landing. This deficiency was particularly critical when rapidly changing weather conditions within the terminal area occurred. These factors generated a need for systems such as RVR which could rapidly and reliably provide reports of the seeing conditions which a pilot could expect to encounter in the touchdown zone and along the runway.
A. RVR measurements are taken by a system of calibrated transmissometers and account for the effects of ambient background light and the runway light intensity. Transmissometer systems are strategically located to provide RVR measurement associated with one or more of the three basic portions of a runway: the touchdown zone (TDZ) portion, the mid runway (MID) portion, and the rollout (Rollout) portion
(1) RVR is an instrumentally derived value which reflects an artificially created seeing condition on or near the portion of the runway associated with the RVR report. This artificially created seeing condition is achieved by using high intensity runway edge, touchdown zone, and centerline lights. These lights increase the conspicuousness of the landing surface and "reach out" to the pilot thereby creating a seeing condition which is significantly better than the reported ground visibility or tower visibility. For any particular fog density, RVR will be significantly greater than reported visibility because RVR is based on the use of high intensity lights. Since RVR is based on high intensity lights, an RVR report only has meaning when associated with the seeing conditions on or near the portion of the runway where the report was obtained (TDZ, MID, or Rollout). An RVR report has no meaning unless a pilot is also seeing the high intensity lights on which the report is based.
(2) To properly apply operating minimums it is important to understand RVR. The following is a list of statements which describe what RVR is:
(a) RVR is an instrumentally derived value.
(b) RVR is currently measured by transmissometers located approximately 400 ft from runway centerline.
(c) RVR is related to the transmissivity (degree of opaqueness) of the atmosphere.
(d) RVR is an approximation of the distance a pilot should see when an aircraft is on, or slightly above, the portion of the runway associated with the report.
(e) RVR is calibrated by reference to runway lights and/or the contrast of objects.
(f) RVR is a value which varies with runway light setting.
(g) RVR is a value which only has meaning for the portions of the runway associated with the RVR report (TDZ, MID, or Rollout).
(3) The following is a list of statements which describe what RVR is not:
(a) RVR is not a measure of meteorological visibility.
(b) RVR is not a measure of surface visibility or tower visibility.
(c) RVR is not a measure of seeing conditions on taxiways, ramps, or aprons.
(d) RVR is not a measure of seeing conditions at or near MDA or DH.
(e) In the U.S., RVR is not measured or reported by a human observer.
(f) RVR IS NOT "VISIBILITY."
FYI: RVR is a value which can be five to six times greater than ground or tower visibility at night and two to three times greater during daytime.
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FAA RVR 概念
