Originally Posted by PPRuNe Radar
As an example, the MEF for the quadrangle containing Dublin is 31. This is based on the highest obstacle, a mast with an elevation of 2890' (380' AGL), plus 300' for unknown obstacles. I assume the CAA round down to the nearest hundred when making this calculation. I guess their logic is that the extra 90' (in this example) should not make a great difference to a VFR flight !!
That's not quite right. The 300' allowance for unknown obstacles would only be added go a ground elevation, not to a known obstacle. It's not the 2,890' amsl mast that's determining the MEF in that quadrangle, it's the high ground at elevation 2,788', plus 300' = 3,088' which then gets rounded
up to 3,100'.
Mark