Just when will Mumbaikars get to ride on an air-conditioned local train? If railway officials from an assortment of agencies that dna spoke to is anything to go by, it could take as early as four months and as late as one year. The fact, all these officials pointed out, was that the AC local was uncharted territory for Indian Railways and secondly deploying it in one of the world's most demanding networks – Mumbai, with its crowds and humidity – was a tough call.

The third reason that is putting pressure on these agencies is that the failure of the AC local in Mumbai can actually dent the Make in India initiative that the Railways so dearly wants to embrace. The railway board has made it clear that the nine AC rake orders with the Integral Coach Factory, Chennai would be constructed only once the trial, testing, commissioning and running feedback from this AC local is obtained.

"A failure could actually mean we are back to a situation where our local trains are either from multinationals like Siemens and Bombardier or we continue to build things ourselves and waste precious time," said a top official.

While messages sent to Central Railway's top authorities did not elicit any response, officials from Research Design Standards Organisation, ICF-Chennai and Bharat Heavy Electrical Ltd refused to put out a date on the commissioning of the train.

"It is a new product and it might take time. We cannot rush the testing of the rake. A delay is better than a half-tested product," was the common refrain of these officials.

Mumbai has had a history of its train trials taking ages. The first Bombardier rake arrived in Mumbai on October 2013 but got commissioned in March 2015, almost 18 months later. The indigenous Medha local which is supposed to run on Western Railway arrived in Mumbai in October 2015 and is yet to be commissioned, almost seven months later.

What needs to be tested?

1. 15-tonne roof-mounted packaging units – railway lingo for AC – in each coach. It will be much more effective than the 10 tonne RMPUs installed in the newly-built double-decker rakes. Most of the trains including Rajdhani, have RMPUs of 7 tonnes2. First-ever fully automatic sliding door mechanism on a local train3. Vestibules that connect six coaches of the rake4. Train control and management system (TCMS) and twin power systems (for running and for ACs, built by BHEL and Netherlands-based Strukton Rail5. The working of all these equipment at a test speed of 70kmph and maximum speed of 110 kmph.