But the biggest question for investors is, exactly what type of airline are they being asked to buy into? Aer Lingus has reinvented itself over the past five years, and with Dermot Mannion now in the cockpit, the airline is veering off in yet another direction.

The ability to change course is a key strength in an industry that moves as fast as aviation. But investors will need a much better view of the final destination before checking in for the Aer Lingus privatisation.

Five years ago it was a bloated outfit with all the bells and whistles that generations of air travellers had grown to expect, plus sky-high fares to match.

Former chief executive Willie Walsh cut most of the frills, and half of the workforce, by transforming Aer Lingus into a leaner player that is better placed to compete with the threat posed by the king of cost-cutting, Ryanair.

Now Mannion wants to put yet another stamp on the airline. He is short on specifics but it seems clear that the relentless cost-cutting of the Walsh era is over and one of Mannion's first moves was a U-turn on previous plans to outsource cleaning and catering.

Given his pedigree at Emirates, a full-frills airline where Dubai's oil-rich Al Maktoum family hold sway, it is hardly surprising that Mannion wants to spruce up the Aer Lingus product. If that means giving passengers something better than the shoddy service Ryanair seems to take pride in, so much the better.

But investors will need to be convinced that there is space for a hybrid airline with more class than Ryanair but without all of the high-cost baggage carried around by British Airways, Air France and the other legacy carriers.

When they eventually get their hands on an Aer Lingus prospectus, investors will be sold a solid growth story.

The airline expects almost to double long-haul capacity by 2010 with new services to the US, South Africa and Asia.

There is huge untapped demand on transatlantic services and, once freed of the shackles of the Shannon stopover and other restrictions in the outdated aviation accord with Washington, Aer Lingus will be able to fly direct to new destinations such as San Francisco, Dallas and Miami.

But no matter how successful the expansion plans turn out to be, Aer Lingus cannot go it alone. Talk of direct services to Australia are pie in the sky if it means you can only travel on Tuesdays and Saturdays, for example. To fill the inevitable gaps in the schedule operated by what will always be a small airline from a small country, Aer Lingus must get back into bed with a bigger partner.

Walsh all but walked away from the One World alliance because British Airways and American Airlines were too greedy, helping themselves to too much of the ticket prices paid by the passengers that Aer Lingus fed into their hubs at Heathrow or Chicago.

The result is that more passengers have to fend for themselves when making connections, never a pleasant experience in a place like Heathrow at the best of times.

If Mannion really believes in his own growth figures, he should be able to persuade his partners to accept a smaller cut in return for all the Irish bums on seats he will be able deliver. Otherwise, there are plenty of other airlines and alliances willing to play ball.

Either way, the government should use its golden share to ensure that a deal is done.

Protecting the national interest does not end with protecting Aer Lingus; it also means ensuring the airline can provide seamless connections to all the places it cannot serve directly.

This might mean the government using its influence to nudge the airline into alliances that might not pay immediate dividends, which would be a bitter pill for an organisation desperate to rid itself of political interference.

But if it makes sense for the state to keep a golden share, it makes sense for the state to use its stake to ensure the airline acts in the national interest.