When Heathrow Connect becomes TfL Rail on 20 May 2018, the switch will happen without the new 345 trains, according to City AM. This is because testing them with a new signalling system has taken much longer than expected.
The trains are now not expected to be rolled out on the line for a few months, to allow time for more testing, and ironing out of kinks.
Even without the shiny new trains, TfL Rail will still take over the Heathrow Connect services as planned. At first, nothing should change about the service except the branding, but once the new trains arrive, frequency will increase to four trains per hour.
Then in December 2018, trains will run from Paddington through central London's new tunnels, through to Abbey Wood.
Howard Smith, TfL's operations director for Crossrail, said:
Our supplier Bombardier continues to test the Elizabeth line trains and the new signalling system in the Heathrow tunnel.
While this takes place we will operate the same service pattern (two trains per hour) to Heathrow as exists now, using the existing Heathrow Connect trains.
We will also run two trains per hour between Paddington and Hayes & Harlington, which is the same frequency as now, using the new Elizabeth line trains. Once Bombardier has completed testing we will increase the frequency to Heathrow to four trains per hour later this year.
This isn't the first time the rollout of the new trains has been delayed. The launch of the 345s on the Liverpool Street to Shenfield branch of the line faced similar setbacks.