David of Broadway wrote:

Tom Anderson wrote:
How about Central to Ealing Broadway, then Heathrow Connect to the
airport? JP puts that at 60-65 min. Slower than the HX, not
significantly faster than the tube, but it works with travelcards and it
avoids a change at Holborn - you have to go over a bridge at Ealing, i
think, but it'll be easier than finding your way through a maze of
twisty little interchange passages, all alike, and should be less busy.
I'm not sure what the frequency of the HC is, though - that 60-65 min
might be based on an optimistic assumption about making a connection.

Unless something's changed recently, Travelcards are /not/ valid on
Heathrow Connect between Hayes & Harlington and Heathrow.

And Heathrow Connect runs on 30-minute headways.

As has already been pointed out elsewhere David's statement above
regarding the limited validity of Travelcards on the Heathrow Connect
service is absolutely correct - nonetheless I feel compelled to
emphasise this point, as if people follow the earlier erroneous advice
they'll end up being the recipients of a £20 penalty fare (IME
Heathrow Connect trains have at least one enthusiastic conductor,
possibly two, who are very efficient in demanding sight of all tickets).