Chapter 5 — CLOUDS AND VISIBILITY 



NWSC 3140/8 Entries 



SKY AND CEILING (COL. 6). — Enter the 

 ceiling and sky cover data in accordance with 

 previous instructions listed for column 3 of 

 MF1-10. 



VISIBILITY (COL. 7). — Prevailing visibility 

 is reported in nautical miles and is determined 

 in the same manner as for surface observations, 

 except that visibility markers, of course, cannot 

 be utilized. In estimating visibility, use radar 

 or stadiometer distance or other distances 

 to known objects, such as ships in company, 

 horizon, etc. For a table which shows the distance 

 to objects on the horizon at sea level in nautical 

 miles, see NAVWEASERVCOMINST 3144.1 

 Chapter IV. 



SKY COVER DATA (COLS. 17 AND 18).— 

 Enter sky cover data for columns 17 and 18 

 in the same manner as in the columns 21 

 and 36 respectively of MF1-10. 



REMARKS (COL. 16). — Enter appropriate 

 remarks in the same manner as in column 13 

 of MF1-10. The major exception to this is 

 that 3- and 6-hourly additive data entered at 

 land stations is not entered in marine aviation 

 observations. 



Recording Charts 



The Cloud Height Set AN/GMQ-13 ( ) and 

 Transmissometer AN/GMQ-10 ( ) recorder 

 records require specific entries and adjustments 

 to be applied to them during their operation. 



The ceilometer (AN/GMQ-13 ( ) ) records 

 should be handled in the following manner: 



1. Enter station name, time check, and 

 date-time (LST) group at beginning and end 

 of chart or any detached portion of chart. 



Enter time check and date-time group near 

 the trace during periods of operation at the 

 time of each 6-hourly observation, when notified 

 of an aircraft accident at or in the vicinity 

 of the station; and when the recorder is stopped 

 or started. 



Enter dual time checks, a date-time group, 

 and an arrow from time check at end of trace 

 to time check at beginning of trace, when ohart 

 is adjusted for time. Make time adjustments 

 when error at time of inspection exceeds 



2 l/2 minutes. Frequency of inspections should 

 be such as to make it unlikely that time errors 

 will reach 5 minutes. 



2. Retain complete ceilometer records for 



3 months after which they may be destroyed 

 unless otherwise Instructed. 



Transmissometer (AN/GMQ-10 ( ) ) records 

 should be handled in the following manner: 



1. Place station name, time check, date- 

 time group (LST), runway number and length 

 of transmissometer baseline at the beginning 

 and ending of each chart. 



Enter a time check and date-time group 

 (LST) at the actual time of each 6-hourly 

 observation. 



Indicate maintenance shutdowns or other 

 periods of nonoperation by inscribing time 

 checks and date-time groups at the end of one 

 period of operation and beginning of the next. 



Enter a time check and date-time group 

 near the trace whenever notified of an aircraft 

 mishap at or in the vicinity of the station. 



Adjust the chart to correct time whenever 

 the time error is 5 minutes or more and note 

 the time of adjustment and a new time check 

 on the recorder chart. 



2. When the transmissometer recorder roll 

 has been exhausted, it should be placed in the 

 empty chart carton. The station name, dates 

 for beginning and ending of roll and runway 

 identification should be entered on the carton, 

 and the used roll retained as prescribed by 

 local instructions. 



CLOUD HEIGHT MEASURING 

 EQUIPMENT 



The accurate determination of cloud heights 

 is a difficult problem to solve under all con- 

 ditions. To aid inobtaining these determinations, 

 several types of equipment have been devised. 

 Some are capable of night determination only, 

 while others provide capability for both day 

 and night observations. The following paragraphs 

 will describe these equipments, their operation, 

 and maintenance. 



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