Lothian and Borders Fire and Rescue Service is to take legal action against the firm which supplied two of its fire engines.
The service said the two combined pump and ladder appliances, costing £450,000 each, were not fit for purpose.
They are too big to negotiate roundabouts and too heavy to drive legally while also carrying water.
The fire service is taking advice as a first step towards legal action against the supplier, GB Fire.
Most of Scotland's other fire services also bought combined machines but from different suppliers.
Central Fire and Rescue Service also used GB Fire. Its combined appliances are now for sale online, for just under £250,000 each.