Yearly maintanence. Train 1,2,3 work from August to September, taken down to one train operation for quiet months after August, with train 1 taken off (or whatever the ones that is in the rota for the year), taken apart and put back together for March next year. That means train 1 is ready for October, so they have one fresh train for next March - Train 2 is then taken off in November and put back together for March, with all trains on the track for March (2 of them being fresh trains so they don't need to be taken apart for another year); then in May Train 3 is taken apart so it's ready for 3 train operation for August with three fresh trains, and the cycle starts again, which is currently where it is, however other problems have stopped 2 train operation for the time being.So it goes 1, 2, 3 available between March and May - 2, 3 between May and July, 1(F), 2, 3 in August, 3, 1(F) in September and 3(F), 1(F), 2 available for October.If that makes sense.