British Airways A318 G-EUNA, which has been under maintenance/in storage at London Heathrow since 21st January, positioned London Heathrow – London City as BA9257 this morning then returned to service operating BA1 London City – Shannon – New York JFK. At Shannon it was discovered that there were issues with the navigation system which was not correctly configured for the Atlantic crossing. There aircraft was therefore unable to continue to New York JFK. Passengers have been accommodated overnight. As a result BA2 New York JFK – London City was cancelled.