UA20 from IAH-AMS arrived more than 3 hours late due to maintenance today. UA 21 AMS-IAH will be around three hours late arriving into Houston.

The previous flight arrived at 5:00 in the morning on the 20th from GIG into IAH with this bird. I don't really understand how then a maintenance issue can arise that then causes a 3 hour plus delay when this plane sat all day in IAH. I know s*it can happen but why not get the plane ready and checked when it lands? I have the feeling that with the number of maintenance issues plaguing the fleet of late that UA does no pre-emptive actions to ensure that the planes are in order. I mean they had more than 10 hours to get this plane ready and it was still more than 3 hours late.

This is getting really old.