Friday, December 22, 2017

Upgrade triggers snarls in air

Dum Dum: Three Calcutta-bound flights had to be diverted on Wednesday afternoon - not because of fog, the usual culprit around this time of the year, but congestion triggered by an upgrade of the main runway at the city airport.

The flights were diverted between 11.30am and 2.30pm, the period when the main runway was closed because of the upgrade and the secondary - also smaller - runway was in operation, airport officials said.

Two IndiGo flights, from Ranchi and Dibrugarh, and an Air India flight from Chennai circled around NSCBI Airport for close to 30 minutes, awaiting a nod to land.

"The pilots told the air traffic control that they did not have enough fuel to keep circling and the flights were diverted to Bhubaneswar," an official said.

The flights came back to Calcutta later in the day.

The official said 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 any collision.
For flights using the secondary runway, the minimum lateral separation has to be 14 nautical miles - 25.928km.

Why are the requirements different for the two runways? "The secondary runway is smaller and has Category I Landing System. The primary runway is fitted with the more advanced Category II Landing System. So, for reasons of safety, the flights scheduled to land on the secondary runway have to keep a greater distance among themselves," the official explained.

On Wednesday, an upgrade of the taxiway forced the officials to further increase the minimum lateral separation for the secondary runway to 20 nautical miles - 37.04km.

"This led to congestion, with flights hovering over the airport waiting to land," a source said.
22/12/Sanjay Mandal/Telegraph