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Why are some MEA’s unidirectional?

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Under IFR, you may use Victor airways to fly your intended route of flight.  These airways usually have a bidirectional MEA which makes sense to me.  But on occasion, you see a Victor airway that has a unidirectional MEA (one altitude for one direction and another altitude for the opposite direction).  What is the rationale behind this?  Why do they need to have different altitudes for the exact same route?

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1 Answers

  1. Best Answer


    John D Collins on Aug 30, 2015

    This is not an uncommon situation when flying into mountainous areas. When a route goes from a lower MEA to a higher MEA, the normal case is that at the boundary fix where the two segments meet, the aircraft is still at the lower MEA and then initiates the climb to the higher MEA. Obstacles and terrain along the route in the direction of the higher MEA are considered and as long as an aircraft maintains a standard 200 feet per NM climb gradient, they are assured of adequate obstacle and terrain clearance in the climb to the higher MEA. When this is not possible, the route designer has a few choices. They can establish a required minimum crossing altitude at the MEA transition fix, or they can raise the MEA of the lower segment. If they choose the latter method, then the question arises, do they need to penalize the opposite direction traffic and not allow them to use a lower MEA. In some cases, they lower the MEA in the opposite direction, because there isn’t a climb criteria to ovoid obstacles in that direction.

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