Dense fog across northern and eastern India has caused significant flight disruptions, leading to cancellations and delays for major airlines including IndiGo, SpiceJet, and Air India. IndiGo alone cancelled 13 flights on Sunday and 57 on Saturday, citing adverse weather and operational reasons. The Directorate General of Civil Aviation (DGCA) has designated December 10 to February 10 as the official fog window, requiring airlines to use trained pilots and compliant aircraft for low-visibility operations.