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apache created the topic: BECMG question
could someone please enlighten me on BECMG I understand the terminology but I still do not know how to apply
ex. TAF YDUK 280033Z 2802/2814 330/10KT 4000 SHRA RA BKN012 BKN020
BECMG 2808/2810 2000 RA SCT035 T21 22 21 19 Q1020 1020 1018 1018
My question is if the arrival time is 0900, which visibility do i use? correct me if i am wrong i think it is 4000
BECMG implies a gradual change and two times are always given. One is the expected time of commencement of the change and the other is the expected time of completion. The rule is simple. You always take the pessimistic view.
If the change is to a deterioration in conditions, you must plan for the worst case commencing early.
If the change is to an improvement in conditions, you must plan for the best case commencing late.
Because you are flight planning on a forecast, you must apply a 30min buffer in case the forecaster got it wrong.
So the OPR for an alternate or holding will apply;
for any arrival within 30 mins of the commencement time for deterioration;
and until 30min after the cessation time for improvement.