IndiGo flight disruptions were not caused by new Flight Duty Time Limitations (FDTL) norms, but by the airline's own internal rostering lapses and "mismanagement", said Civil Aviation Minister K Rammohan Naidu to the Rajya Sabha on Monday. He highlighted that revised FDTL rules were functioning smoothly for a month before December 3 crisis occurred. "We'll take strict action," he added.