New Delhi, Dec. 10 -- Shares of InterGlobe Aviation Ltd, promoter of IndiGo airlines, have dropped about 15% since 1 December, as flight cancellations jumped from roughly 200 at the start of the crisis to over 1,000 by 5 December.

IndiGo cited a multitude of "unforeseen operational challenges", primarily crew shortages triggered by the new flight duty time limitation (FDTL) rules that took effect for all airlines in November. These rules are designed to prevent pilot fatigue by capping flying hours and mandating rest periods.

As India's largest airline with roughly 65% of the domestic market share-and therefore the highest pilot requirement-IndiGo has been hit the hardest. The carrier's long-standing model of maximum utilization of exis...