The runway at Patna airport. Telegraph picture

Patna, May 4: The air traffic control (ATC) at Patna airport has issued a NOTAM (Notice to Airmen) to operators, informing them that the services of instrument landing system (ILS)/glide path would not be available for a fortnight.

As a result of the notice, issued four days ago, an aircraft will get permission for landing at the airport only if the visibility is at least 2,800m.

Having been declared as one of the most critical airports of the country because of its short runway length and obstructions in the approach funnel, the Patna airport normally allows landing of aircraft if the visibility is 1,600m and above.

“We have issued the directive as the instrument landing system/glide path is under maintenance,” a source in the ATC told The Telegraph.

ILS helps pilots at the time of landing by identifying the position of the runway on which the touchdown has to be made. It also helps in deciding the glide path. Its absence means pilots have to depend on the navigation system available in the cockpit and they have to judge the touchdown position and glide path manually.

Patna airport has CAT-I ILS, which allows landing when visibility is 1,600m and above. Incidentally, CAT I ILS has been put in place at Varanasi and Lucknow airports too. But at these airports, aircraft are given permission to land even if the visibility is 1,200m. But permanent obstructions in the approach funnel at Patna airport prevent that.

Giving reason for undertaking the maintenance work of the ILS, the ATC source said the signals emitted by the system were not being properly received by the aircraft. Also growth of vegetation at the zoo end of the runway, where the ILS is fitted, and vegetation outside the airport premises may have prompted the move.

“We have started levelling work on the zoo end of the runway. If this solves the problem, the old visibility norms would be restored within a fortnight,” he added.

He, however, said in case the cause for the problem was vegetation growth outside the airport premises, then the Airport Authority of India (AAI) would have to depend on the state government, as only the state authorities can prune such vegetation.

“We would inform the state government if required,” he added.

Things would become clearer only after calibration of the ILS, which would be done after completion of the levelling work at the zoo end of the runway. AAI uses its aircraft to calibrate the functioning of the glide path.

Operators are not yet complaining about the revised visibility norms but many of them said that if the maintenance work failed to give desired results within a fortnight, they would face problems. “When it rains heavily, the visibility at Patna comes down to 1,000m. With no ILS in place, it would become virtually impossible for aircraft to land here. We hope things will become normal soon,” said an official of a private operator.

Official of another operator, however, appeared more concerned. “If things revert to normal after levelling work inside the airport is over, then it is okay. But if the corrective steps require the permission of the state government, the wait is going to be longer, as the government does not appear to be too interested in taking corrective steps to keep the Patna airport functional,” he said.