In Maintenance Field Which Situation is Very Much Pressure to handle problem?

if the system running 24/7 and no way to accomplish the maintenance work while the system running.

and if the system stoppage for a very short time, where the maintenance work needs more time.

it will make additional pressure.

Very critical situation arises when system needs to run,not to stop but maintenance is necessary

When there are machine troubles and they need some output for their productions. It added some pressure.

when any part is expired no new part is awalable in near marcket

I think is a situation where the production and standing because of the holidays for me because of an electrical malfunction complicated.