Aer Lingus will have to find an impressive chief executive quickly if it is to win support from the investment community for its flotation. Ultimately, the new chief executive will have to be someone who has the ability to drive a total change in culture at the organisation and focus it on delivering shareholder value.

Skills which were considered crucial for previous incumbents - such as an ability to keep both politicians and the airline's staff happy - are no longer the prerequisite for the job, according to fund managers.

Mr Frank O'Brien, an independent investment consultant, said it was imperative that the new chief executive was fully aware of the radical cultural change required to transform a State-owned company into a privatised company. A new chief executive must also quickly begin to achieve value for its shareholders, Mr O'Brien said.

Aer Lingus will be seeking someone with considerable experience in the airline sector, and preferably someone who has successfully steered a privatisation or major restructuring at another carrier. And while the company is relatively small within the aviation industry, some analysts suggest the prospects of an imminent flotation may allow it to offer a sufficiently attractive incentive and remuneration package.

Mr Cullen's resignation comes at a time when some fund managers have begun to question publicly the viability of floating the company on the stock markets. Last week, Hibernian Investment Managers said it believed the Government had missed the best time to float Aer Lingus.

Hibernian's head of equities, Mr Bernard Swords, said it would not buy Aer Lingus shares when they were floated unless the price was "very low". The company believes the outlook for airlines is bleak, given a combination of rising oil prices, falling fares and increased competition.