Numerous cancellations today due to staff shortages from early afternoon until close of service - not great for people returning from half term hols.
There's a lot of extras between Paddington and Hayes and Harlington though ... suggests that cl.387 or diesel unit(s) are in use - and I'm guessing that route knowledge / type clearance might not be there for Heathrow?
DMU's are out of the question as they are no "section 12" approved ie they are not fire rated to operate in the Heathrow tunnels, the 387 will not have been route cleared. Also if there is a shortage of Connect staff GWR staff will not be much help as the drivers and conductor / guards will not have route knowledge.
Looks like the 140 busses were busy then