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Even as the number of fog hours this winter at the Delhi International Airport Limited (DIAL) is expected to be lower than in the previous year, the intensity of intermittent adverse weather conditions has resulted in an increase in disruptions in flight operations.
“The number of fog hours in December and January (till 6) this winter stood at 35 hours and 22 hours, respectively. Last winter, 40 fog hours were recorded in December and 70 hours in January. The total numbers of fog hours this season would be lower, but there are extreme weather conditions such as those recorded on Sunday (January 5), the impact of which does not get highlighted in this data,” said a senior executive at IGI Met.
The Met department maintains a diversion index to determine the impact of dense fog on flight operations. The index is the ratio of the number of flights diverted to the number of dense fog hours in CAT IIIB conditions. According to sources at DIAL, the diversion index had declined to 0.53 in 2012-13 from a peak of 2.5 recorded in 2007-08. However, the diversion of 52 flights on Sunday alone has meant the index has trebled to 1.46 in the current financial year.
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“The duration of dense fog hours at the airport on Sunday was the highest (13 hours) since January 3, 2010 (14 hours). This added to the fact that the number of flights operated at the airport has increased to 900 per day from 600 in January 2010 impacted operations,” added the executive. Till Saturday, only 31 flights had been diverted this winter. However, on Sunday alone as many as 52 flights were diverted, the highest recorded in a single day since December 25, 2010 (when 40 flights were diverted). As many as 463 flights (arrivals and departures) were delayed on Sunday and another 137 flights cancelled.
“An aircraft can land if runway visibility is 75 metres with CAT IIIB. For take-off , visibility requirement is 125 metres. But this time, the fog was so dense that even arrivals were affected,” said a senior airline executive.
Fog conditions are expected to set in again on Thursday at DIAL, after which the Met expects normal visibility conditions at the airport. Overall, the Met department has predicted 80-100 hours of fog with 15-20 days of disruption at the Delhi airport, compared with the 140 fog hours recorded last year.
Meanwhile, in a bid to minimise delays in the current season, the Airports Authority of India (AAI) and DIAL have integrated collaborative decision-making procedure (CDM) with each other. CDM involves airport operators, airlines, ground handlers and the air traffic control (ATC) collaborating and sharing data through an automated system to improve airport efficiency. Airports officials expect the combined decision-making would help them improve utilisation during the fog period.
According to data available with ATC, on an average, airport capacity reduces by 40 per cent due to increase in runway occupation time during the dense fog period, which is likely to improve with combined decision making. Another airport executive said, “We cannot do anything to hasten procedures during dense fog hours. But CDM would allow us to minimise delays once weather conditions improve. Besides, often, there is a cascading effect due to disruption of operations at other airports. With CDM, we can manage that better.”
While Delhi allows landing even amid dense fog when visibility is low, fog at the airports in the northern and eastern part of the country delay flight operations, causing consequential delays. These airports do not have the advanced instrument landing system such as CAT-III in place and, hence, no operations can take place during dense fog.
