Climb
It is covered by BLR's (bid line rules) which mainline pilots work to as covered in our MOA (memorandum of agreement).
Draft assign as it is called was designed for extreme circumstances and in my 11 years in BA has been seldom used.
However for a variety of reasons, not least that BA are under established, there are now problems covering work at certain times of every month and this DA is being used on a monthly basis to keep the operation going.
It is a very divisive system. The guys hate it and the ops guys hate it but it was never designed to be used in this way.
However, if you have half a brain avoiding the call if fairly easy, as we are now wise to the tricks BA have resorted to to contact us.
For every trick, we have an answer.
Still some people blindly answer the phone when they know its going on and then whinge when they get caught.