Fog affected flight operations at Jayaprakash Narayan International Airport on Wednesday as the first flight, which was scheduled to land at 7.55am, landed at 10.55am.

Conditions of several other flights remained the same as low visibility disrupted landing and take-off of Air India, Go Air and IndiGo flights.

The Patna-Delhi route appears to be the most affected as both cities are engulfed in fog particularly in morning hours. Flight operations were adversely hit as visibility reduced to less than 500m in the morning hours. An airport official said: "As against the required visibility of at least 1,200m, the visibility was less than even 200m till 8am on Wednesday, causing several flights getting delayed."

The GoAir G8 134 flight scheduled to leave Patna airport for Delhi at 8.25am left on Wednesday at 11.28am. Similarly, the G8 140 flight from Delhi to Patna scheduled to arrive here at 11.30am landed at Patna airport at 1pm.

Similar, was the condition of other carriers.

The Indigo 6E339 flight from Calcutta to Patna arrived one hour late at 11.19am while the Patna-Calcutta IndiGo 6E634 flight departed 4 hours and 30 minutes late at 2.38pm against scheduled departure time of 10am. The Air India Delhi to Patna flight AI 409 was also 30 minutes late as it reached Patna at 12.25pm.

Due to delayed arrivals, several flights scheduled for evening hours also were re-scheduled on Wednesday.

The Delhi-Patna Indigo flight 6E 5192 arrived Patna at 6.15 pm, one hour late as its departure time from Delhi itself was delayed by an hour. Similarly, the Indigo 6E 633 -Patna to Lucknow - flight departed one hour late at 8.55 pm from Patna airport.

A few flights operating from Patna airport have also been cancelled while timings of a few others have been re-scheduled in the wake of the prevailing foggy conditions. GoAir would stop operating its morning Delhi-bound flight from Patna airport from Thursday till the weather conditions improve. The first flight of GoAir for Patna (G8 140) would now leave Delhi at 10.35am and arrive here at 12.10pm. Meanwhile, IndiGo has cancelled its flights on Thursday on the Patna-Delhi route.

The short runway at Patna airport is one of the major factors responsible for delayed flight operations. Patna airport is marked as one of the most critical airports in the country due to its short runway and obstacles in its approach funnel. Against the runway length of 2,286m (7,500 feet), only 1,954m (6409 feet) remains available at the time of landing because of location constraint of the airport.

The fog witnessed for the past 3-4 days is mainly due to the western disturbance, said a weatherman adding: "The passage of a western disturbance and a depression in the Bay of Bengal have changed the wind pattern to easterly, which has increased humidity levels. The combination of these factors has created the dense fog across northern India, including Bihar."

Though every year fog disrupts timings of flights operating from Patna airport during winter, the situation continues to be same more or less despite India Meteorological Department (IMD) in June this year installing Drishti - an indigenously developed transmissometer that can record exact visibility readings for pilots even when visibility is less than 1,200m.

Airport director Rajendra Singh Lahauria said: 'We are taking steps to improve flight operations under poor visibility conditions. Besides Drishti, tarmac lights have been installed on an additional stretch of 220m ahead of the runway to improve flight operations under poor visibility conditions."