Good morning. I am just wondering what the current policy is on using your Oyster Card to travel for free on the London Underground and TFL Rail and Heathrow Express services between the Heathrow Airport terminals? Does your card have to have credit on it? If so how much? Will a card without any credit work? Will a card that is loaded with a Bus & Tram Pass season ticket instead of any credit work? Does anyone know these answers? Any information is appreciated. I can't seem to find the answers to these questions. Thank you very much.