I am puzzled as to why, when on a train for Heathrow, passengers are
advised to "get of and change" at Hounslow West station if they are on
a T5 train and want T4, and like wise if on a T4 train and want T5.
Why not ask them to change trains at Hatton Cross station?
This is nearer to Heathrow and has the advantage that in the event of
a failure on the tube service, there are many buses available at that
station for the airport terminals.