I have impression I have diffilculties to make me understand
Have no worry. One of the difficulties with any discussion involving folk without an idiomatic common language is making sure that what one is saying is what the other is hearing and comprehending and that applies for both people. Just means that we take a little bit longer to work through a discussion and that is fine.
nevertheless, for Airlingus C= 500
This suggests that the two trimsheets are not the same. I need to see the other trimsheet to check if that is the case or if, for instance, the 500 reference is in error.
So I deduct the only data which is able to explain difference between two register is LEMAC
LEMAC is a fixed position, defined by the OEM design. This cannot be the cause, I fear.
Your calculations are fine.
However, we don't have enough information to work out where the apparent error comes from. You will have to let me see both the trimsheets so that I can compare them. At this stage, the likely answer is that you are trying to treat two different designs as the same and that just won't work.
Can you scan both the trimsheets you are working with and email them to me ? That way there can be no confusion regarding just what data you are working with.