New Delhi: As many as 66 flights were cancelled at the Delhi airport on Friday due to fog and low visibility conditions. Several airlines cancelled 66 flights to and from Delhi due to fog and reduced visibility conditions, a source said. Of them, 32 were arrival flights, and the remaining 34 were departure flights, the source said. Aviation regulator DGCA has announced the period from December 10 to February 10 as the official fog window during this winter.