A jawan scanning Calcutta airport for explosives ahead of chief minister Mamata Banerjee's return from London on Thursday fell to his death through a gap in a glass walkway that had been camouflaged with a polycarbonate sheet.

Gora Charan Singh, a 40-year-old Central Industrial Security Force (CISF) jawan from Mayurbhanj in Odisha, was walking through what airport officials described as a service corridor in Level 1 of the terminal around 2.45pm when he crashed head first onto the basement.

Singh's head was smashed in the 12ft fall from the arrival lounge to the basement, where various airlines and agencies have their offices. He was declared dead on arrival at a private hospital near the airport.

Singh had been scanning the service corridor beside Gate 5B with a handheld metal detector when the incident occurred. Unlike the housekeeping staff who use the service corridor, Singh wouldn't have been aware that a broken glass panel on the walkway had been replaced with a polycarbonate sheet.

Sources said the glass panel broke a long time ago - in 2013, according to some - and was never repaired. "The walkway is mostly used to place mechanised ladders that the housekeeping staff use to scrub and clean the glass façade. The polycarbonate sheet had been placed to ensure that if any cleaning tool slipped out of a worker's hands, it wouldn't fall to the basement through the gap. The workers knew about it and so wouldn't step on the sheet," a senior airport official said.

What he couldn't explain was why there was no signage warning someone using the walkway that a glass panel on the floor was missing. The camouflaged gap hadn't been cordoned off either.

Chief minister Mamata, who arrived less than two hours after the incident, examined the broken portion of the walkway. "It is a very unfortunate accident. My condolences to his family," she said.

Singh, a member of the CISF's bomb detection squad, was transferred to Calcutta from Mumbai airport in 2012. He lived in the city alone.

An official of a private airline said it was shocking to know that a broken glass panel on the walkway hadn't been repaired for so long. "Although the walkway where the incident occurred isn't part of a passenger area, anyone new to the terminal could have strayed into the corridor and stepped on the flimsy sheet," he said.

The bridge between the boarding gates and the business class lounge in the international section also has a glass floor. There are a few more smaller glass walkways in the security hold.

Maintenance has been an issue at the state-run airport even after the integrated terminal became operational in March 2013. Several glass panes in the façade have crashed over the past two years, some within striking distance of passengers.

Rainwater leaking through the roof joints of the steel structure has also been a source of embarrassment.