Initially, Postern, the group of company doctors of which Mr Coulson is a founder director, will conduct a five-week review estimated to cost pounds 90,000. It should identify the actions needed to improve the group's trading position, strengthen working capital and build a new management team.
Postern was called in by shareholders representing more than 40 per cent of the equity, including the Miller family which founded the company.
Mr Coulson said the company had plenty of orders but production bottlenecks had developed and there was a shortage of working capital. He plans to stay at Prestwick for about a year.
Prestwick made a loss of pounds 3.97m in the year to 31 July, although it was reported to have returned to profitability in September. This compares with a pounds 91,000 profit the previous year.
Shareholders' funds fell from pounds 10.5m to pounds 6.3m at the year end, while borrowings rose to pounds 7.6m. Gearing was a hefty 121.7 per cent.
Wayne Osman, chief executive, left in June. John Gilhooly was appointed executive deputy chairman shortly afterwards. Mr Gilhooly has now stepped down to make way for Mr Coulson.
The shares rose 1p to 42p.