Liverpool Street changes & 9 car on the Eastern side are a big logistical challenge so focusing on that being successful might be more important in the short term given both testing and the Eastern side will both require large numbers of 9 car units. Hence much easier to uplift testing after the Eastern side 7 car units can be converted.
Not sure how many trains remain at 7car (is it about 23?)
So ought to be about 47 full length units (if fleet is 70units) and no reason why they can’t all have had software updates by May
By the time of the changeover would there be any difference in tunnel test sets and a standard 9 car set. I mean could they be used interchangeably by that date
Whilst the changeover might be a temporary logistical challenge (physically moving them to/from Ilford) not sure it will be a big problem, presumably in the few days preceding the number of 7car units can be slightly cut (as wont need to keep reserve units).
Presumably would only take hours to split a set, shunt in the extra 2 cars, and recouple it. However would then need the 9 car software loaded and commissioned and train tested which would take some time before use. I’m guessing checking the train is working properly as a newly lengthened 9car set might be a testing distraction for a while. But does the Eastern and Western service plus a few units for central testing require more than the 47? 9car units
What I am trying to query is how much testing capacity might be lost whilst lengthening goes on, as I suspect not many days when 50+ units have been out of the sidings at same time