AEROGRAPHER'S MATE 3 & 2 



Table 5-5. — Reportable visibility values (Miles) 



Increments of Separation (Miles) 



1/16 



• 1/8 



1/4 



1/2 



1 



5 







3/8 



1 1/4 



2 



2 1/2 



3 



10 



15 



1/16 



1/2 



1 3/8 



2 1/4 



3 



4 



11 



20 



1/8 



5/8 



1 1/2 



2 1/2 





5 



12 



25 



3/16 



3/4 



1 5/8 







6 



13 



30 



1/4 



7/8 



1 3/4 







7 



14 



35 



5/16 



1 



1 7/8 







8 



15 



40 



3/8 



1 1/8 



2 







9 





etc. 



HIS VISIBILITY VALUE IS 

 ATTAINED OR SURPASSED 



HROUGHOUT HALK OF THE 

 HORIZON CIRCLE. 



THIS VISIBILITY VALUE IS 

 ATTAINED OR SURPASSED 

 THROUGHOUT AT LEAST 

 HALF OF THE HORIZON 

 CIRCLE. 



209.215 

 Figure 5-3. — Illustrative examples of determi- 

 ning prevailing visibility. 



Control Tower Visibility 



Unless otherwise exempted, certified tower 

 personnel will report prevailing visibility when 

 the prevailing visibility at the usual point 

 of observation or at the tower level is less 

 than 4 miles. These observations may be 

 used immediately for aircraft operations. As 

 soon as practicable they should be recorded 

 on a graphic transcriber, MF1-10, or separate 

 form with the time of observation, prevailing 

 visibility, remarks, and the observer's initials. 

 It should then be forwarded to the weather office. 



Weather office personnel should also advise 

 the tower as soon as possible when the surface 

 visibility decreases to less than, or increases 

 to equal or exceed 4 miles. Weather office 

 personnel should also re-evaluate weather 

 station prevailing visibility, as soon as practi- 

 cable, upon receipt of a differing tower value, 

 and upon receipt of subsequent reportable 

 changes in tower visibility. They shall also 

 use tower values at stations where the ob- 

 server's view of portions of the horizon is 

 obstructed by trees, buildings, etc. If a surface- 

 based obstruction to vision that is uniformly 

 distributed to heights above the tower exists, 

 it will constitute a sufficient reason to classify 

 the weather station's prevailing visibility to 

 be the same as the towers. 



Runway Visibility (RVV) 



Runway visibility is the visibility along 

 an identified runway. Where a transmissometer 



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