Are the problems more with the 67s than the MkIV? Just wondering if it could be solved by sourcing different locos?
Neither are especially problematic anymore, particularly in service its a long while since any failed. They have faults the same as every other train but as there's no real spare sets the slightest problem means a substitute unit, this happens with all fleets but its more obvious when a 150 subs for a Mk4 set than it is when one subs a 158 or 175. They're few and far between now but there are Still swaps due to lack of crew knowledge, if there's nobody available to cover and the booked driver doesn't sign 67s then the choice is cancel or send a unit out, normally for most of the day to keep the cycle going. It has happened twice this week.
The vast majority of the out of use sets is because the exams on the sets which take place every 11 days the set is out are often taking 3 days rather than the planned 2, there's also a delay in getting some parts.
Most of the exams are carried out at ATC Crewe which means that with 5 sets active, there is 15 days worth of exams to carry out every 11 days. If set is on its exam and another reaches its max days then its out of service waiting its slot. Some have been able to be carried out at Canton but generally they're at Capacity too.
A new regime is being implemented where, after a heavier B exam the sets can run for 28 days rather than the original 11 which should lighten the load and should in effect double to amount of available sets. HD01 is the first through that and it now has 28 calender days between exams rather than 11 service days.
There's currently 4 diagrams for 5 sets, the 5th is on maintenance so any issue knocks a diagram out.
A large supply of parts is also making its way into the system now which should also reduce Downtime.
For example today HD04 is on its exam at Crewe until Sunday and will be released for 5V33 on Monday morning, HD02 is on Canton for tyre turning, neither of those are faulty but it means only 3 sets available for the 4 diagrams.
Once HD03 and 07 are available there will be 5 diagrams but from 7 sets giving one on maintenance and one on repair/spare at any time. There's also a possibility of HD08 being introduced which would then able 6 diagrams from 8, again giving an extra out of Service rake.
Effectively at the moment it requires 100% availability to Cover all diagrams.
The locos are now going for a suite of Mods as well. 67013 ran to Crewe ETD on Thursday for a C exam and to become the first through these 'Reliability mods' which will implement things learnt in service.