What the modernised Mumbai and Delhi airports have had from Day 1, Calcutta's integrated terminal is to get after 1,026 days of operation. And it is still just a promise.

Inline baggage scanning, a basic facility whose absence forces fliers to queue up before X-ray machines and benefits nobody other than the additional manpower deployed there, will start in the international section of the terminal by January, senior officials said on Monday.

If that happens, it will be the end of a frustrating wait for fliers using the so-called modernised airport since it opened on March 11, 2013, with the same old baggage-scanning system that airports across the world have long discarded.

"The Airports Authority of India (AAI) has approved the proposal to replace the X-ray machines with the new system, although initially it will be only for international passengers. Domestic passengers would have to wait a few months more for the facility," an official said.

Travellers don't have to line up to get their check-in baggage scanned at X-ray counters in airports equipped with inline scanning. They can go straight to an airline's check-in counter and drop their baggage on the belt. Scanning happens in several stages even as each piece of baggage travels on the conveyor belt to the hub from where it will go into the belly of the aircraft.

Calcutta and Chennai are the only two metro airports in the country persisting with the conventional X-ray scan for baggage before check-in. The other common link between the two airports is that both are run by the AAI.

At the privatised Delhi airport, inline baggage scanning has been available since the new terminal became operational in July 2010. In Mumbai, inline screening was introduced a couple of years before the new Terminal 2 was opened in February 2014.

Both Delhi and Mumbai have benefited from their private operators planning in advance and investing the extra money required to upgrade the baggage screening system for fliers to use from Day 1.

In Calcutta, the babus running the behemoth terminal that looks grand from outside took their own sweet time understanding that an inline baggage scanning system is a given in any modern airport, just as escalators, walkalators and elevators are.

For more than a year after the integrated terminal opened, the airport authorities allegedly did little to bring inline baggage scanning.

An inline system costs around Rs 30 crore for a terminal of the size of Calcutta airport, which is a fraction of the Rs 2,500 crore spent on building it. But in a government-run facility, the first cost-cutting measures invariably are facilities meant to make the airport experience better for a flier.

"We had been asking for inline baggage scanning long before the new terminal became operational," said Captain Sarvesh Gupta, the chairman of the Airline Operators' Committee, Calcutta.

While other airports were cutting down on queue time, Calcutta cited one excuse after the other for not having an inline baggage scanning system - from "security concerns" to "lack of initiative in Delhi".

Metro has been highlighting the problems faced by fliers in the absence of an inline baggage scanning system since the time the integrated terminal opened.

Most people flying out of Calcutta for the first time realise after standing in a check-in queue that they have to line up elsewhere to get their baggage scanned by an X-ray machine. Airlines now have signage in front of the check-in areas asking passengers to get their baggage scanned before approaching the counters.

On an average, a traveller needs 35 to 40 minutes during the morning rush to reach the security hold after completing check-in. The duration of this process at Mumbai and Delhi airports varies between 20 and 25 minutes.

In 2014, Calcutta airport had sent a proposal to the Delhi headquarters of the AAI, seeking an upgrade to inline screening. Delhi allegedly ignored the proposal and Calcutta didn't push it. The airport continued to use the age-old system despite complaints from fliers and airlines.

A survey team from Delhi finally came down to Calcutta before Durga Puja and sanctioned the proposal to upgrade the baggage scanning facility. "We have received permission to install two additional X-ray machines and a conveyor belt," an airport official said.

An inline system has four levels of scanning. If something inside a piece of baggage raises suspicion during the first two phases of scanning, it is put through the next two levels.

The existing software at Calcutta airport is capable of scanning 70 per cent of the baggage received daily. The remaining 30 per cent has to be scanned manually by trained personnel. "But new guidelines say that 100 per cent of baggage needs to be scanned manually by screeners in levels 1 and 2," an official said.

Based on this requirement, the new X-ray machines would send images to the screeners and if they have any doubts, then a bag would be sent for the next two levels of screening, which would also be done manually.