Capital city Delhi remained under cover of dense fog, recording the longest spell this season. Runway visibility dropped below 200mtr for over 12hrs between 7pm on Monday to 2pm on Tuesday. Horizontal visibility and the runway visual range (RVR) lowered to 50mtr for quite sometime, disrupting the scheduled air traffic.
Prolonged poor visibility resulted rescheduling of arrivals and departures, delay and diversion of flights. The 'low visibility procedure' was put in place from 7pm onward on Monday and continued till 11am next day. The visibility was least from mid night on Monday till early morning on Tuesday.
In poor visibility conditions, all airports resume ILS (instrument landing system), facilitating landings, popularly called CAT-III procedure. At Palam airport, 3 runways are equipped with ILS, namely runway 11, 28 and 29. Specially qualified, trained and CAT-III compliant pilots are permitted to carry out marginal visibility operations during landing and take-offs. The CAT-IIIB compliant pilots get clearance for landing in visibility, as low as 50mtr with a decision height of 15mtr. However, for take-offs, the threshold visibility requirement goes up to 125mtr.
Western disturbance is arriving over the northern mountains on 29th Dec and stay put till 30th Dec, with very limited effect over the plains. Weather conditions are likely to get better in terms of fog and temperature, in the plains of North India, including the capital city during this period. Passage of the western disturbance will be followed by fresh spell of dense fog and cold wave conditions, commencing 31st Dec and spilling over more intensely, during 1st week of January 2023.