ACN-PCN Relation and Calculation

[CURAviation]

Dear all,

I just read an archived thread about PCN values and runway usage. I saw that member Overrun had some good explanations. I'm not that active yet on this forum which is why I ask my question here again regarding PCN values.

I read that an aircraft can land on a runway with a higher ACN value compared to the runway PCN. How can this be determined? I thought that the PCN could never be exceeded by the ACN. If an aircraft lands on a runway with a higher ACN on a frequent basis, how can it be calculated how often such aircraft are allowed to land on the runway?

Overrun, can you explain this to me in more detail? Many thanks.

Edit: What do the different letters mean, such as F, B, X, U, A, W, T? I assume these letters can be used in all combinations depending on the calculation and/or condition of a runway?

Best regards,

CURAviation