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Old 2nd Apr 2021, 17:54
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Banana Joe
 
Join Date: Jan 2018
Location: Amantido
Posts: 712
It's very important to fill that in when you have a high QNH and mandatory for a VNAV flown approach. The FMC receives data from the barometric altimeter, and at the transition level VNAV will recalculate its profile showing you are too high i.e. a QNH of 1023 will leave you 300 ft high.
A high QNH will move the T/D further away from the E/D point, a low QNH will move the T/D closer to E/D point.
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