December 9, 201213 yr I still don't follow. Altitude constraints and vertical paths are constructed with respect to altitude above MSL. With the correct QNH selected on the EFIS panel you'll be flying with respect to the same altitude. How would the setting in the FMC change that? Correct me if I am wrong but I think the fmc calculates a vertical path based on a number of parameters one of which includes atmospheric pressure, I'm guessing standard pressure, then when the correct pressure is set in the efis when for example descending through the transition level the plane will either descend faster or slower to recapture the path. You can make it more accurate by inputting the destination airport qnh in the fmc and that will give you a better prediction on the vertical path Bryan Richards "People depend so much on automation that they forget how to get the automation to work." B.W.
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