Getting to grips with performance says:
In the event of an aircraft system failure, known prior to dispatch and affecting
the landing distance, the available runway length must at least be equal to the
required landing distance with failure. This distance is equal to the required landing
distance without failure multiplied by the coefficient given in the MMEL, or to the
performance with failure given by the Flight Manual.
This calculation is only used for dispatch.
Suppose that you have flaps locked and your actual landing distance is 2300m
and then find rwy with distance 1.67*2300
