Mine Mystery ( cameo), Tidy-Up Time! ( cameo), A Treat for Trying ( cameo), Tunnel Trouble and Naughty or Nice? Series 5 - Baa! ( does not speak), Toby and the Flood, Thomas and the Rumours ( does not speak), Oliver's Find, Sir Topham Hatt's Holiday and Make Someone Happy

However, he still had a bit of a rivalry with Percy. Once, when the Mail Train was threatened to be scrapped, rumours began to spread that Harold would make the deliveries instead. However, Thomas and Percy worked even harder than ever to prevent that from happening and Harold's chances of taking over the mail run were stopped when the unpredictable strong winds caused him to be grounded. Harold flew by at Tidmouth Sheds for a routine flyby and greeted the steam engines, accidentally spreading sneezing powder all over Thomas, Splatter and Dodge, dumped by Diesel 10. In earlier scripts, he did not speak and he spread quarry dust in the quarry bowl all over the three engines. The engines were just leaving the station, when they heard a familiar buzzing. " I say you two, there's news flying about!" " Where?" puffed Percy. " All over the place. They're going to scrap the Post Train/the Mail Train and use me instead. Wings work wonders you know! Always!" " Rubbish!" huffed Thomas.Airship ( does not speak), Autumn Leaves ( does not speak), Blown About!, The Telescope ( does not speak), Rusty's Rescue!, Playful Passengers ( cameo) and Henry's Hairy Passenger ( cameo) Thomas' YouTube World Tour - A World Around You, Navigation, Never, Never, Never Give Up, Thomas' Anthem and That's What Friends are For Series 3 - Percy's Promise, Thomas, Percy and the Post Train, All at Sea and Thomas and Percy's Christmas Adventure Monster Mistake ( does not speak), Caroline's Cruise, Passenger Plane, Sparkling Sky, Old and Useful ( cameo), Harold's Holiday and Disgusted Diesels Top 5 Non-Railway Vehicles ( does not speak), Thomas the Helicopter and Thomas and the Birthday Surprise

Series 14 - Henry's Health and Safety ( cameo), Being Percy ( cameo), Jumping Jobi Wood! ( does not speak), Jitters and Japes ( cameo) and Merry Misty Island Series 24 - How Does it Work?, Fall is So Much Fun, The Little Engine Who Believed and New Year's Day with Thomas Harold also speaks in a manner reminiscent of an RAF pilot, using terms such as "wizard" and "old chap" in conversation.Harold's theme in the second series is a musical variation on the main score of the 1955 film, The Dam Busters.

Series 16 - Race to the Rescue ( cameo), Express Coming Through ( does not speak), Sodor Surprise Day ( does not speak) and Welcome Stafford! ( cameo)

When Thomas' brakes failed while boarding at a station, Harold chased him down the line with an inspector.