It was allowed to fly because you are allowed a certain number of defects (ADDs) standing for Acceptable Deferred Defects. These have a time limit by when they have to be fixed. If the limit is exceeded, the aircraft is grounded untill it is fixed. The defects on this aircraft were not being cleared, so as soon as it was no longer legal to fly, it was grounded. Air Scotland tore up the agreement, and moved to Air Holland, by far a much more professional company!!
Eff Oh.