With Season 5, the decision was made to write a full series of original, staff-written stories, without using the Railway Series' books as a source. One reason for this was producer Britt Allcroft's desire to create a theatrical Thomas the Tank Engine movie, and requested that director David Mitton show off his modelling skills.
Some inspiration for the episodes came from a former LMR manager named David Maidment. In 1997, Maidment met with Steven Wright about the possibility of supporting the Railway Children charity, and while Wright told him the series' staff commonly received such requests, they would consider. During their meeting, Maidment relayed stories about his railway experiences working in South Wales and as the manager at Crewe station. Maidment received a call asking if he would allow some of his stories to be used as material – the stories from The Railway Series were frequently based on true events, and Allcroft and Mitton preferred this. Maidment agreed, and was also asked to review each story to make sure that the railway in the show operated realistically. As a result, Maidment received writing credit alongside Allcroft and Mitton. 10,000 pounds later was donated to the Railway Children for his work.
The design for each new character would be chosen by David Eves, and given to David Mitton for approval. For ease of filming, Season 5 would introduce larger-scale versions of the narrow gauge engines, and from Season 6-12 these larger models were used almost exclusively. Originally, the character Bertram was supposed to be a tank engine, but financial difficulty in building a new model made them repaint Duke's model with Smudger's face.
- Cranky Bugs - Cranky causes trouble for Thomas and Percy.
- Horrid Lorry - Three horrid lorries start taking over the engines' work.
- A Better View for Gordon - Gordon complains about the plainness of Kirk Ronan station.
- Lady Hatt's Birthday Party - The Fat Controller urgently needs to get to Lady Hatt's birthday party.
- James and the Trouble with Trees - James is careless around some trees.
- Gordon and the Gremlin - "Gremlins" start causing problems for Gordon when Dowager Hatt visits.
- Bye George! - George causes grief for Thomas, Duck, and Gordon.
- Baa! - Percy meets a ram, who manages to help out when a station is trashed.
- Put Upon Percy - Percy complains that he is overworked and gets into a predicament in the mines.
- Toby and the Flood - Toby gets in a dangerous position when a dam bursts.
- Haunted Henry - Edward spooks Henry with a tale of a mysterious ghost.
- Double Teething Troubles - Derek, a malfunctioning Diesel, causes more trouble than he is worth for Bill and Ben.
- Stepney Gets Lost - Stepney gets lost on the way home.
- Toby's Discovery - Toby goes exploring and makes several odd discoveries.
- Something in the Air - Henry ignores Thomas' warning about a dangerous line.
- Thomas, Percy and Old Slowcoach - Thomas and Percy save an old coach from scrap.
- Thomas and the Rumours - When Harold is chosen to take a special visitor around Sodor, the engines fear they will be replaced.
- Oliver's Find - Oliver makes an amazing find on an old branch line whilst taking the mail.
- Happy Ever After - Percy makes a "good luck package" for Mrs. Kyndley's daughter's wedding.
- Sir Topham Hatt's Holiday - The Fat Controller goes on holiday.
- A Surprise for Percy/A Big Surprise for Percy - Percy moans about his work in the mines, but he is in for a surprise.
- Make Someone Happy - James tries to think of others and takes Mrs. Kyndley on a "mystery tour".
- Busy Going Backwards - Toad wants to go forwards for a change.
- Duncan Gets Spooked - Rusty tells Duncan a ghost story.
- Rusty and the Boulder - Thumper causes chaos when he dislodges a boulder.
- Snow - Rusty tells Thomas about snow and how Skarloey managed to survive it.
- Bill and Ben
- Annie and Clarabel
- S. C. Ruffey
- Sir Topham Hatt
- Lady Hatt
- Stephen Hatt
- Bridget Hatt
- Jem Cole
- Mrs. Kyndley
- Peter Sam (does not speak)
- Henrietta (does not speak)
- Donald (cameo)
- Trevor (cameo)
- The Refreshment Lady (cameo)
- Nancy (cameo)
- Tom Tipper (cameo)
- Wilbert Awdry (music video cameo)
- Douglas (music video cameo)
- Diesel (music video cameo)
- Daisy (music video cameo)
- The Diesel (music video cameo)
- Sir Handel (music video cameo)
- Duke (music video cameo)
- Bulstrode (music video cameo)
- Bulgy (music video cameo)
- Old Slow Coach
- The Horrid Lorries
- Old Bailey
- Dowager Hatt
- Derek (not named)
- 'Arry (not named)
- Bert (does not speak)
- The Ghost Engine (does not speak)
- Bertram (does not speak)
- Butch (does not speak)
- Thumper (does not speak)
- Tiger Moth (does not speak)
- This was the first season of several things:
- The first season not to have any episodes based on The Railway Series stories by Wilbert and Christopher Awdry.
- The first season to introduce original characters not created by Wilbert or Christopher Awdry.
- Alec Baldwin's first season as narrator.
- The first season not to air on Shining Time Station due to the show ending. Episodes from Season 5 were instead aired on FOX Family's Storytime with Thomas.
- The first season to use a Proteus 2000 to compose the music.
- The first season not dubbed in Finnish or Ukrainian.
- The first season to air in Canada.
- The first season that Douglas does not appear since his debut in the second season. Although, he does appear in a music video from this season.
- According to an interview with David Mitton before his death in 2008, this season was supposed to be a showcase of Thomas and the Magic Railroad.
- Production of this season began after Wilbert Awdry died in March 21st, 1997, but ended sometime in the later half of either 1997 or 1998.
- This was also the final season of several things:
- Britt Allcroft's final season as writer and producer.
- David Mitton's final season as producer.
- Angus Wright's last season as executive producer.
- The last season shown on Cartoon Network UK, besides syndicated episodes that would still be shown on the channel until 2001.
- The last season filmed completely in 4:3 full screen.
- The last season to have a railway consultant.
- This was also the only season of several things:
- The only season not to have Knapford Station as a destination.
- The only season to have Kirk Ronan as a destination.
- The only season that Diesel does not appear in since his debut in the second season, though he does appear in a music video from this season.
- David Maidment's only season as railway consultant and writer.
- The only season where Donald appears, but without Douglas.
- The only season where Donald appears, but doesn't speak.
- Michael Angelis was not credited in the opening titles for the UK narration. However, he is credited as narrator in the Hindi narration, even though it was redubbed.
- This season's official episode order differs from the aired order.
Behind the Scenes