Tyne & Wear Metro .. Why so may 'Not in Service' trains today

I was at Monkseaton station this afternoon, shortly after 13:00 and two trains passed, one iin each direction which were 'Not in Service'

Then at about 14:30 I was at Palmersville and again two 'Not in Service' trains passed while I was at the station

Seems a lot more than normal

With the Airport line closure, green line trains that would usually go to Airport are instead running Not In Service from South Gosforth to Monkseaton and back. I believe there was also driver training running NIS today.

hopperelec said:

With the Airport line closure, green line trains that would usually go to Airport are instead running Not In Service from South Gosforth to Monkseaton and back. I believe there was also driver training running NIS today.

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Oh, I see .. many thanks!

Seeing as Regent Centre is unavailable I would imagine the possession limits take out the access to the West Neck of the depot (where you could otherwise reverse).

Without totally ripping up the timetable and rewriting the whole lot the most logical option is empty to and from Monkseaton siding where you just about slot into the next scheduled run south at the same time as if you'd done a passenger service to/from Airport.