If you want to find out exactly why Disney decided to make Planes, its brand new spin-off from Pixar's Cars series, don't ask a film critic. Don't ask the cinemas either - both Cars films had relatively weak showings at the box office. No, if you want to find out exactly why Disney decided to make Planes, you'd be better off asking the staff at your nearest Toys R Us. After all, Cars remains the most successful film in history when you account for merchandise revenue. There are Cars toys, Cars furniture, Cars cutlery and even a Cars potty available for those children who cannot piss without the comforting sound of an engine running.

There can be no denying that Planes is little more than a cynical ploy to extend such merchandising - so far the stores have been mercifully empty of toy planes with quirky grins and self-assured eyes. The disappointment is in just how poorly Disney has hidden their motivations. The film follows Dusty Crophopper, a young crop-dusting plane that couldn't have been more obviously named if he had been a jet fighter named Shooty McBulletgun. Dusty wants to throw aside his destiny in farm work for a more glamorous career in - you guessed it - racing. He enters a local qualifier for the Wings Across The World race and, through the disqualification of a fellow competitor (in a poorly judged gag hinting at athletic doping), finds himself competing on an international stage. Cue the usual challenges and successes as the naïve young plane fights to prove himself and win over the hearts of the other contenders. It starts exactly as you'd expect, continues along exactly as you'd expect and, dare I say, finishes absolutely exactly as you might expect.

The problem with Planes is exactly the same problem that plagued both of the Cars films - by creating a world in which everyone is a vehicle, the only admirable goal for a character to succeed at is to win a race. No child will sit and watch ninety minutes of Dusty learning the importance of his role as a crop-duster just as no child would have spent the duration of Cars watching Owen Wilson's race car character settle down and appreciate the pleasures of a small town life. The film's inherent dullness stems entirely from these limitations.

Tied to this tired plot, Planes attempts desperately to liven itself up with colourful characters. Desperate is the operating word, here. The big race is an international event, and as such is inhabited by very obviously international characters. A Mexican plane never seen without his colourful wrestling mask, for instance. Or perhaps the British plane voiced, uninspiringly, by John Cleese. Working on an animated film must work perfectly for Cleese - whose performance might have quite literally been phoned in.

On every level, Planes is a money-making film. It was conceived for money, written for money, directed for money and acted for money. Not once will you feel that an ounce of passion went into the movie. As a result, Planes is, in every sense, an average film. It is never dull, but it is never exciting. It serves exactly the purpose it is supposed to and will entertain its target audience for exactly ninety-one minutes. Let's be clear, though - if ever a character from Cars has a single original adventure, the credit will go entirely to the child holding the Dusty Crophopper toy.