Harold was obsessed with aircraft and was Bio-fused into a Sikorsky S-55 helicopter. His Bio-fusion process went well, but the staff had to ban him from being allowed to attempt flight after what had happened to Mavis. After not being used for a few years, Harold was used to transport injured rail staff to a hospital after Gordon exploded.
However, as soon as he struggled to lift off the ground, Harold suddenly started bleeding from his propeller, fell to the ground and exploded.
Harold's accident was due to most of his lower extremities permanently fused to his propeller system. As such, his vital organs were drawn into the motor, tearing him apart from the inside.
- According to Pauls Vids, during the production of Shed 17 his brother thought Harold's rotor blades should be connected to his gonads, but at the time Paul thought that was going too far.
- Harold's model hasn't yet appeared in any series other than Shed 17, even though it can be used in regular Thomas Episodes.