The winter flight schedule to dog the fog is out.

All four operators — Jet Airways, GoAir, IndiGo and Air India — would start their winter schedule from this Sunday (October 27).

About the difficulties in operation of aircraft at Patna airport during winter, Atul Singh, executive director of Delhi-based Centre for Aviation, Policy, Safety and Research, said: “During winter, pilots mostly depend on instrument landing system (ILS) for navigating the aircraft. The ILS helps pilots at the time of landing to identify the position of the runway at which the touchdown has to be made. The ILS at Patna airport is of Category-1 (CAT-I ILS). According to standard operating procedure, the “runway visual range” — minimum visibility for operation of aircraft — for CAT-I ILS is 1,600 metres. But because of the foggy condition with the onset of winter, the aircraft are not able to meet this visibility condition in the morning hours.”

“Based on the observation of the present weather system, we are expecting that fog would start forming not before October 30. The level of moisture is quite high at present and wind direction is also easterly, which is highly moist. The wind direction is expected to change to dry westerly only from November 1, after which the moisture content might also start reducing — a condition conducive for fog formation,” said Ashish Sen, director, India Meteorological Department, Patna.

Sources in Air India claimed that though their winter schedule would be in effect at Patna airport from October 27 but there would not be any changes in the timing of its four Delhi-bound flights from the city. “There is no change in the timings of the four flights as of now,” said Satish Bhage, station manager, Air India Patna airport.