Continuity mistake: The sign says: "Danger - engines must not pass this board." When Thomas passes it, "board" is replaced with "point."
Continuity mistake: Gordon's connecting rods change position after he pulls Thomas out of the mine.
Other mistake: When Thomas shunts Annie and Clarabel his eyes look wonky and Annie and Clarabel are missing their names.
Answer: Breakdown trains help the engines back on track.