A CALMAC ferry that has missed thousands of sailings this year due to a major mechanical failure has missed her scheduled return date — again.

MV Argyll Flyer — which plies the Gourock-Dunoon run — was supposed to return to service on Monday following a six-month absence to have her broken propeller replaced.

But CalMac bosses have pushed that back by a further week because the vessel is now subject to 'a period of intensive crew familiarisation', according to the company's website.

The Flyer was laid up in April without a working propeller and has failed to make more than 2,000 scheduled sailings since then.

She had initially been due to resume sailings in May, and then September, but her return was pushed back again to October 25 and has now been further delayed to 'the week commencing November 1'.

Asked by the Telegraph why the intensive crew familiarisation was not completed within the previously declared October timeframe, CalMac said its estimate was 'slightly' out.

A spokesman for Scotland's national ferries operator said: "The Argyll Flyer is undergoing required sea trials, crew familiarisation and equipment trials ahead of her return to service.

"This has taken slightly longer than originally estimated as we work to ensure that all crew are fully trained and the vessel meets the necessary performance criteria.

"We expect to have her back on the network week commencing November 1."

The tiny 78 gross tonnage boat MV Ali Cat — which can only sail in clear, calm conditions and in a sea state which causes only moderate rolling and/or pitching — has plied the run solo.

There have been a number occasions since April when the route has had no vessel because Ali Cat has been unable to cope with windy weather — leaving passengers with delayed journey times and having to use a replacement bus on Western Ferries.

Passengers will still have a one-vessel service for a period after the Flyer's much delayed return because Ali Cat will then be pulled from the service to undergo her own 'planned upgrade works', CalMac has confirmed.

The company's passenger-only service between Gourock and Dunoon has endured around 15,000 cancelled sailings since 2011 through a mixture of mechanical failures and its vessels being too light to cope with certain conditions.