Siliguri, Jan. 9: Take-off and landing was not possible at Bagdogra airport today because of fog and the absence of technology that helps operations during poor visibility, causing inconvenience to around 4,000 people including Bhutan Prime Minister Tshering Tobgay.

Tobgay, who took the 1.40pm Indigo flight from Calcutta to Bagdogra after attending the Global Bengal Business Summit, returned to the city at 3.30pm because the flight could not land.

Between 10.30am and 4.30pm, 10 flights could not take off and 10 more had to turn back. The only plane that landed at Bagdogra was Druk Air's Paro-Bagdogra-Bangkok flight. The sole international flight to use Bagdogra airport landed at 1pm and left for Bangkok half an hour later.

Other than the Bhutan Prime Minister, who was supposed to travel to Thimphu by car from Bagdogra, others whose flights had to turn back included Darjeeling's BJP MP S.S. Ahluwalia and Union micro, small and medium enterprises minister Kalraj Mishra.

Rakesh Sahay, the director of Bagdogra airport, said: "Visibility was around 1,000 metres today. If there is no Instrumental Landing System (ILS), the minimum visibility required is 2,100 metres."

"The airlines have accommodated most passengers in tomorrow's flights," he added.

Because of frequent cancellations at Bagdogra for poor visibility, the Airports Authority of India (AAI) had four years ago decided to install the ILS. Later, the Indian Air Force, which manages the runway and the Air Traffic Control at Bagdogra, announced that it would take over the project.

The ILS enables planes to land and take off even if visibility is around 350 metres. It is a ground-based technology that guides an aircraft through a combination of radio signals and high-intensity lighting arrays to enable safe landing and take-off.

However, the system is yet to be put in place as 1.28 acres of the 24.16 acres needed for the project is yet to be acquired because of resistance from five families.