It all started monday night when 137 was cancelled.
A 77W was sent as a replacement. The original plan was for it to return as 142 the next morning. However....
854 broke down as well.(Fin740)
The 77W from YYZ operated 854 almost 8 hours late.
Tuesday morning 142 was operated as a 321. And an extra section E90 with the overflow.
Eventually fin 740 was back in service as 148 to YYZ.