Just wondering, could it be that a bi-mode multiple unit with no power cars (meaning that all the traction equipment has to be stowed beneath the carriages) that is also capable of 125mph and good acceleration on diesel is just a bit difficult to achieve? Then you add in the restrictive UK loading gauges and a slightly incompetent DFT and you're left with a train that two years after introduction, is still suffering from issues...
How do the sets compare in regards to reliability to other brand new trains and are the 801's doing better?
The HST was still suffering from issues a lot longer than two years after introduction, to the extent that around 1980, BR asked Mirlees Blackstone to develop a rail-friendly version of the MB190 diesel engine, with a view to replacing the Paxman Valenta, which was suffering persistent faults. This eventually resulted in four power cars being fitted with the MB190.
The 5 car would have been working it’s booked diagram, seeing as a 10 car is comprised of 2x 5 cars (two diagrams) it’s just that the other diagram would have been uncovered due to unavailability. That 5 car was always going to be on that working regardless.
Some people still can’t get their heads around that if it were fixed rakes of 9 or 10 vehicles then it would be a full cancellation not just a shortformed service! Ideal it is not but surely you would rather get on a 5 car and be on your way than have your train cancelled and a full trainload of passengers have to wait for the next train and cram on with that full trainload!
If Hitachi can successfully send out the required & correct formations every day then obviously this situation would cease (obviously there would be the odd one due to train faults etc)
Also important to remember that many people in the West of England and South Wales still seem not to realise that their HST turning up as booked was, on occasion, a direct result of other services, notably in the Thames Valley/Oxford/Cotswold Line corridor getting short formed so that an HST could be made available to appear at Bristol, Swansea or Penzance - with a random selection of a 180, a three-car Turbo or even a two-car Turbo replacing the HST on its original booked duty.
On at least one occasion, Old Oak Common even turned out a Hull Trains Class 180 to cover the 17.50 from Paddington to Worcester, so the diagrammed HST could replaced a faulty HST on another route.