Calcutta: A delay in the arrival of a software from Japan for an upgraded signalling system is likely to defer the launch of East-West Metro's first phase.

The railway authorities blamed BEML, the Bangalore-based PSU that is manufacturing the rakes for East-West Metro, for the delay.

The first phase of East-West Metro was scheduled to become operational by October this year.

But now trains are likely to start running between Salt Lake Sector V and Stadium stations only in end-December and that too without the platform screen doors functional, sources in the Kolkata Metro Rail Corporation (KMRC), the implementing agency for the East-West Metro, said.

Mitsubishi Electric Corporation of Japan has been assigned the contract for developing the software for train control and management, which will integrate signalling system and platform screen doors with the train's braking system, power and other vital functions, officials said.

The new signalling system will allow trains to run at a gap of one-and-a-half minutes. The earlier system, approved in 2011, allowed a maximum frequency of two-and-a-half minutes.

"BEML was late in providing the details to Mitsubishi. The Japanese company was supposed to provide the software in May but now it will be available by the end of August," a KMRC official said on Tuesday. Once the system is integrated with the train and the signalling system, trial runs will have to be executed.

The final version of the software that will integrate the train with the platform screen doors will be available only in end-December.

"So, we are planning to keep the screen doors non-functional initially. Once the full version of the software is available, the screen door integration can be carried out at night," the official said.

BEML officials were unavailable for comment. The PSU manufacturer was given the contract after Madrid-based Construcciones y Auxiliar de Ferrocarriles (CAF) opted out of the project because of rejection of its cost-escalation claim.

Till the new system is implemented, trains cannot run faster than 25km per hour, officials said. The speed in the final version will be 60km per hour.

It had initially been decided that East-West Metro would run on Continuous Automatic Train Control System, in which track circuits are used to the determine the location of the train. But, in the middle of 2017, it was decided that an upgraded version, communication-based train control system, would be installed.

"The on-board equipment will be different. The train's system will communicate with the signalling software and the train will run on the basis of that. So, a train will not move if it finds another train at less than permissible distance," said an official. "Trains will be able to run closer to each other. The safety system would be better."

"It might take a few more months for the trains to run but there are likely to be long-term benefits," said another official.