Hi Mohat,
There is no monitor(MN) variable for critical. Even if there were I don't think it would behave the way you expect. For example:
The critical path can move dynamically minute to minute. The job that fails may or may not be on the critical path at that time. Five minutes later it might become critical.
Possible solution:
It is possible to use the TAG field to denote CRIT and LATECRIT values for a job Ex. CRIT23. When the job fails parse it to find that it is CRIT 2 and LATECRIT 3