Dum Dum: Calcutta airport authorities have tweaked the main runway maintenance plan to reduce flight diversions.

The main runway was closed for operations usually for three hours, twice a week, for routine maintenance work. At that time the secondary runway was used for flights to land and take off.

But the taxiway that aircraft normally use to vacate the secondary runway is currently closed for operations. So, planes are taking double the time to clear the runway, causing congestion in the air, an airport official said.

The authorities decided to change the maintenance schedule following several complaints from various airlines and the air traffic control.

"Instead of three hours twice a week, we will keep the main runway closed for two hours thrice a week," an airport official said on Monday.

The diversions took place in the third hour, when flights faced fuel shortage after being kept on hold mid-air for long, the official said.

"The backlog got created in the first two hours... in the third hour, several flights had to be diverted because of a long waiting time," Captain Sarvesh Gupta, chairman, airline operators' committee, Calcutta airport, said.

The maintenance work of the main runway is crucial to check wear and tear and the instrument landing system. It has to be carried out during the day, the airport official said.

Metro had earlier reported how on December 21 three Calcutta-bound flights had to be diverted because of congestion triggered by the maintenance work.

The minimum lateral separation between two consecutive flights landing on the main runway has to be 7 nautical miles or 12.964km. It means when a flight touches down on the main runway, the next in line to land has to be at least 7 nautical miles away in the air to prevent possible collision.

For flights using the secondary runway, the minimum lateral separation has to be 14 nautical miles or 25.928km because the runway is smaller and has only category I instrument landing system. .

An upgrade of Taxiway F forced officials to further increase the minimum lateral separation for the secondary runway to 20 nautical miles or 37.04km.

Aircraft use this taxiway to vacate the secondary runway.

"Since it's closed, they had to use another taxiway and it took a long time to clear the secondary runway," the airport official said.