There are actually two QR Tilt Train engines required by Alan in his contracts:
1.) QR Tilt Train E engine in Alan #41
2.) QR Tilt Train D engine with a complete Tilt Train Diesel set in Alan #60
In Alan #41 you are required to send him the QR Tilt Train E engine only, for more information about this engine please check http://trainstation.wikia.com/wiki/QR_Tilt_Train_E
Then after a few contracts , in contract #60, you are required to send Alan a complete Tilt Train Diesel set which consists of following items:
1x QR Tilt Train D engine
12x QR Tilt Power Car wagons
1x QR Tilt Car wagon
It often happens that a player working on Alan #60 sends him a set consisting of wrong wagons (usually belonging to the Tilt Train Electric set). For this reason we recommend checking if the train set sent to Alan is a complete Tilt Train Diesel set and all the wagons as well as the engine really do belong to this set.
You can find more information about this train set here: http://trainstation.wikia.com/wiki/Tilt_Train_Diesel