The sale of a 49 percent stake in the world's biggest airports operator has been flagged as the largest initial public offering in Europe this year and a litmus test for domestic investor faith in an economic recovery.

If it goes ahead, it will be the first time that part of a share offering on the Madrid stock exchange will be directed at retail investors since the 2011 listing of lender Bankia, which was bailed out by the government a year later.

"The operation is moving forward. There is no problem with investor demand," an Aena official told Reuters, adding that the prospectus would be filed next Friday.

The group is sticking to its planned stock market debut on Nov. 12, but would have a shorter offering period and roadshow than first envisaged as a result of the one-week delay, he said.

"Legally they have to bring a series of documents and they haven't presented all of them," a spokeswoman for Spain's stock market regulator said on Friday.

It also needs government approval to go ahead with the listing. The Aena official said the green light is expected to come at the government's weekly cabinet meeting next Friday.

Aena, which operates airports in Spain and Latin America and will soon hold a majority stake in the UK's Luton airport, is expected to list at a premium to its European peers.

Earlier on Friday, a report from the public body advising the government on privatisations showed a preliminary price range for the sale at between 41.50 euros and 53.50 euros a share, implying a market value of between 6.2 billion euros (4.88 billion pounds) and 8 billion euros.

HIGH VALUATION

The Spanish government had initially considered a 5 billion euro valuation for Aena but three core shareholders chosen this month put it at 7.3 billion euros to 8 billion euros.

The group has undergone a huge overhaul to ready itself for privatisation and its 2013 profit of 597 million euros was its first since the start of the financial crisis. The company's debt stood at 12 billion euros at the end of last year.

Based on these figures, Aena would have an enterprise value of between 18.2 billion euros and 20 billion euros, or 11.7 to 12.8 times 2013 earnings before interest, tax, depreciation and amortisation (EBITDA).

That would be higher than the group's main European competitors, with Germany's Fraport valued at 10.7 times EBITDA at the end of last year and France's ADP valued at a multiple of 10.5, Thomson Reuters data show.

The top range of the valuation is also higher than the price offered by two of three core shareholders, which are set to buy a combined 21 percent of the company.

Ferrovial offered 48.66 euros per share, while British fund TCI offered 51.6 euros per share. The third core shareholder, Corporacion Financiera Alba, offered a price of 53.5 euros per share.

According to the report, 90 percent of the offering will be reserved to institutional investors, while 1 percent will be earmarked for Aena employees and the remaining 9 percent will go to retail investors.

The firm hopes to lure investors with the commitment to pay half its profit in dividend.

A recent recovery in passenger traffic after Spain returned to growth last year following a long recession, a booming tourism sector, higher navigation tariffs and a reduction in group costs have also backed the sale.

But a one year lock-up period imposed by the state, a lack of political visibility over the future public ownership of the operator as well as restrictions on the shareholders' capacity to influence the firm's strategy were also a drag for many potential investors.

(Additional reporting by Robert Hetz and Andres Gonzalez; Writing by Tracy Rucinski; Editing by David Clarke and Elaine Hardcastle)

By Julien Toyer and Carlos Ruano