A pair of battery-operated tugs designed to tow away trolleys has reduced the airport’s dependence on contracted workers notorious for shirking and ensured that passengers do not have to fret over finding the racks empty during rush hour.

Before the tugs were deployed, one each in the departure and arrival areas, trolleys would be manually retrieved. But passengers would often find the racks empty and trolleys scattered all over the place.

“The two tugs have been in use post-Durga Puja and they do make the trolley-retrieval process more efficient. Two more are expected soon,” an airport official said on Wednesday.

This isn’t the first time that tugs are being used at the airport for trolley retrieval. Five of them were damaged and never repaired.

For the state-run airport, a task as basic as trolley retrieval has been a challenge for as long as anyone can remember. Complaints about passengers not finding trolleys when they need them did not end even after the airport moved to the new integrated terminal. Maintenance of trolleys has also been a peeve point.

Six facility management companies have handled the trolley-retrieval contract at different times over the past 11 years, but there has been little change in the quality of service because the employees have remained the same. Trolley workers backed by unions have been known to act as touts, offering to help passengers move their luggage for a fee.

Airport officials said they were taking steps to discipline the trolley retrievers. Metro had reported in May about 10 trolley retrievers being banned from entering the airport after it was found that they had crossed retirement age but were still around.

Six more were removed recently. The number of trolley retrievers has declined from 84 a few years ago to 64, officials said.

Since the electric tugs came in, passengers have felt the difference. “I remember running from one section of the terminal to another to find a trolley. When I passed by this time, trolleys were there where they should be,” said Tarak Mondal, who lives in Muscat and visits Calcutta every year.

Officials of several airlines said the flood of complaints from passengers about missing and broken trolleys appears to have finally stopped. The tugs are used every 10 minutes.

An official of Aroon Aviation, the private agency currently handling the trolley maintenance and retrieval contract, said a tug typically tows away around 90 trolleys at a time, although the stack can be longer.

Another 600 trolleys are to be soon added to the 3,600 in use.