This winter, fliers are a relaxed lot. The credit goes to Airports Authority of India for its decision to relax the minimum visibility norm for flight operations from the city airport, prompting fewer plane cancellations and delays.
The fliers are happy over the timely arrival and departure of flights on most of the days despite fog. Monu Agarwal, a city-based businessman, said: “I faced frequent flight cancellations last winter. This time, planes are getting delayed at times, but cancellation is rare.”
A few seemed apprehensive over relaxation in the visibility norms. “Reducing the visibility criteria from 1,600m to 1,200m — a relaxation by 25 per cent — has increased the risk factor by 25 per cent as well,” said Arindam Guha, director, Expression Buildtech Private Limited, Patna.
Airlines are, however, delighted after the relaxation in the visibility criterion. “Till the last year, we used to cancel almost all morning flights because of poor visibility. But this winter, we are operating some of them by extending their operations by a few hours,” said an executive of a private airline.
The flying experience in the winter has been quite bad in the recent years, when the minimum visibility criterion was 1,600m. The flight operations used to start as late as 2pm during the peak winter season (December 15 to January 15), when dense fog usually envelops the city till 12noon. On few days, the first flight landed in the city at 6pm and four to six flights were cancelled because of dense fog.
Taking into count the frequent disruption of flight operations at Patna airport owing to foggy conditions during peak winter season, the airport authority recently reduced the minimum visibility requirement for flight operation from 1,600m to 1,200m. Sono Marandi, director (in- charge), Jayaprakash Narayan International Airport, Patna, told The Telegraph on Friday: “The visibility conditions have been reduced from 1,600m to 1,200m at Patna airport.”
The aviation terminology for minimum visibility criterion is “runway visual range (RVR)”. The RVR of 1,600m in simpler words means that flights are allowed to land only when the pilot is able to make a visual contact at 1,600m.
The RVR is one of the two determining factors for operation of aircraft. The other factor is the decision height — the altitude from where the pilot has to decide whether to land or to take a turn around.
“During the winter season, pilots mostly depend on instrument landing system (ILS) for navigating the aircraft. The ILS helps pilots at the time of landing as far as identifying the position of the runway at which the touchdown has to be made. The ILS at Patna airport is of category- 1, which is termed as CAT-I ILS. According to the standard operating procedure, the RVR for CAT-I ILS is 1,600m. The visibility criterion was kept at 1,600m for this reason. But owing to the foggy condition with the onset of the winter, the aircraft were often not able to meet this visibility condition in the morning hours, leading to delay in their operation. Thus, with the relaxation in the visibility, the airlines would now have extra time for flight operations in foggy weather,” said Atul Singh, the executive director of Delhi-based Centre for Aviation, Policy, Safety and Research.
Another reason for high visibility requirement at the city airport is shorter stretch of approach lighting system, commonly called tarmac lights. The tarmac lights at the city airport are installed on a stretch of 210m prior to the runway. Ideally, the stretch should be 420m, which allows the flights to land with visibility at 800m or less.
Sources said the reason behind the shorter stretch of tarmac lights is land shortage. “We cannot install more lights because Airport Road starts immediately after the runway. The probability of installation of these lights on the Phulwarisharif approach is also minimum because of the railway tracks,” said a senior executive at the airport.