Behala: A revised rule that requires any construction within 22sq km of the Behala Flying Club to get a no-objection certificate from the Airports Authority of India (AAI) has led to a slowdown in municipal sanction of building plans in one of Calcutta's realty hotspots.

The construction red zone around the "non-operational" flying club used to be barely 2sq km before a software upgrade by the AAI this year dragged as many as 16 wards into its span.

While a plot being in the red zone does not automatically disqualify it as a potential construction site, even a single-storey structure must now be cleared by the AAI before the building plan is submitted to the civic authorities.

"The Calcutta Municipal Corporation (CMC) isn't accepting any application for new constructions within the red zone without the AAI's no-objection certificate. And getting that certificate is a cumbersome process. To know the latitude and longitude of your plot, you either have to visit the Survey of India office on Park Street or hire an expert in the field. You then submit the information to the AAI and wait for the certificate before you send the building plan to the civic authorities for approval," said Animesh Chandra Guriya, an architect working on projects in Behala.

A CMC engineer said most of the localities in the red zone are to the west of Diamond Harbour Road, including Parnasree, Rabindra Nagar, State Bank Quarters, Becharam Chatterjee Street, Biren Roy Road (West), Sarsuna, Shakuntala Park, Sakherbazar, Silpara, and Sri Ramkrishna Colony.

Some of the areas in the red zone to the east of Diamond Harbour Road are Bata Colony, Ramachandra Pally and Sarada Pally. Parts of the Garden Reach-Metiabruz belt where the AAI has clamped height restrictions include Paharpur, Brace Bridge, Nature Park, Fatehpur and Dewan Bagan.

According to a civic engineer, nearly 500 approvals for new buildings are granted every year in the places that have been included in the red zone.

In the yellow zone that surrounds the red one, a building of up to 41.5 metres or 13 storeys high can be built without the AAI's clearance. "Beyond that, you will need a no-objection certificate," the engineer said.

The yellow zone includes Alipore, Chetla, the Joka tram depot and Diamond Park.

Height restrictions on construction in the vicinity of an aviation facility are usually along the "approach funnel" of the runway and meant to ensure the safety of aircraft. Behala Flying Club, as the AAI's website mentions, is currently a "non-operational airport". There has been talk of using the flying club as a second airport for the city, but nothing has materialised yet.

A civic official said the CMC's building department never received an official communication from the AAI about the red zone being widened. "We chanced upon the new rule only last month. Many building plans in Behala were sanctioned between January and June without the CMC being aware of the rule tweak."

The Bengal government has written to the AAI for the no-objection norms to be eased.

"The change in the rules was done at the headquarters," said K.L. Sharma, the executive director (eastern region) of the AAI.

A colour-coded map showing the different zones is available under the "NOCAS menu" on the homepage of the AAI's website. "Anyone can access the website's no-objection section and give the latitude and longitude of a particular place and it will automatically show whether that area falls under the red zone," a senior official said.