British Airways Boeing 747-436 G-CIVV operating BA174 New York JFK – London Heathrow (depart New York JFK 14th August) diverted via St Johns, Newfoundland in the early hours of this morning due to a medical emergency on board. Crew did not have sufficient hours to reach London Heathrow and the aircraft therefore further diverted to Dublin where a substitute crew had positioned to take the aircraft on to London Heathrow.