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domcheung created the topic: Shaded grey box for instrument approach
You say if this box is shaded grey and you can get the actual QNH from an approved source such as ATIS or AWIS, you may reduce the published MDA by 100 feet .
My question is if the QNH is from a TAF eg QNH 1015 hpa . I guess this QNH is not regard as the actual QNH . Am i correct
bobtait replied the topic: Shaded grey box for instrument approach
No, a TAF gives a forecast QNH that is OK for flight planning (alternate requirements etc,), But when it comes to actually flying the approach to MDA with the TAF QNH, you must use the published figure because that assumes you are going to use the TAF QNH. However you may reduce the published figure by 100ft only if you have the actual QNH.
Note that in this case, you are not flight planning - you have actually arrived and are in the process of flying the approach. As long as you can be sure that you can get the actual QNH, you can take 100ft off the published figure.