If the RVR is not reported, what meteorological value should you substitute for 2400 RVR?

Question

If the RVR is not reported, what meteorological value should you substitute for 2400 RVR?

BlackTom AI · Accepted Answer

Begin by identifying the core question: when RVR (Runway Visual Range) is not reported, what substitute visibility value should be used for a reported RVR of 2400? 
Option 1: 'A ground visibility of 1/2 NM.' This option uses 0.5 nautical miles as the substitute. In aviation meteorology, when RVR is missing, the prevailing visibility is used, and sometimes guidance provides a substitute value that aligns with typical RVR ranges. However, the common substitute related to a 2400-foot RVR is not expressed in nautical miles, so this choice is questionable and likely incorrect as the standard substitution is not specified in terms of NM here.
Option 2: 'A ground visibility of 1/2 SM.' Here the substitution is 0.5 statute miles. This aligns with the commonly taught rule that when RVR is not reported, a visibility value around 0.5 statute miles (2400 feet of RVR is roughly 0.45 miles, so 0.5 mile is a reasonable proxy) can be used as a substitute for planning and briefing, and it matches typical shorthand used in some procedures.
Option 3: 'A slant range visibility of 2,400 feet for the final approach segment of the published approach procedure.' This option mentions slant range visibility, which is not the standard substitute for missing RVR. Slant range concerns line-of-sight distance at an angle and is not used as a substitute for RVR in the final approach segment when RVR is unavailable. Therefore, this choice is incorrect.
Reassess: The phrasing in many aeronautical references indicates that when RVR is not reported, the substitute global visibility value is used, and 0.5 statute miles (0.5 SM) is commonly cited. The option using 1/2 SM matches this idea, while the 1/2 NM option would be inconsistent with the typical substitution practice, and the slant range option describes a different concept altogether and is not the substitute for RVR in this scenario.
In summary, evaluating each choice: Option 1 misstates the unit of the substitute, Option 2 correctly identifies a half-mile replacement commonly used as a practical substitute, and Option 3 introduces slant range terminology that does not apply to substituting for missing RVR in this context. The reasoning favors Option 2 as the appropriate substitute, with Option 1 and Option 3 being inaccurate for this purpose.

If the RVR is not reported, what meteorological value should you substitute for 2400 RVR?单项选择题

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