A confidential document shows that Aer Lingus expects to raise €530 million for the airline from the flotation later this month.

The figure is contained in a memorandum agreed between management and unions concerning a new supplementary pension fund at the airline. The memo discloses that, even if the flotation fails to reach "the anticipated financial outcome", a supplementary pension fund will be set up anyway.

Various valuations of the airline have been suggested, with advisers to the flotation hoping for between €850 and €950 million. However, some fund managers have described this as too high and have suggested a more "realistic" figure of €600 million.

Because of the nature of the sale, the airline will be a beneficiary, along with the Government. The airline is issuing new shares to fund business development, while the Government will dispose of some of its existing stake. The €530 million refers to the proportion of the sale proceeds the airline itself hopes to gain. The Government's potential share of the proceeds is not known at this stage.

The latest document suggests Aer Lingus is expecting a high valuation. The Government has yet to decide how much of its stake it is to sell, but Minister for Transport Martin Cullen has indicated it will hold on to at least 25.1 per cent. This is designed to protect "key strategic interests" such as the Heathrow slots.

The shares will be offered for sale on the Dublin and London stock exchanges, with a private placement in the US. The price range for the shares will be issued shortly. Many fund managers believe there is a danger that if Aer Lingus prices the shares too high, it will have to reduce its valuation subsequently. This happened during the recent Ipo of Air Berlin.

In recent days, the director of human resources at Aer Lingus, Liz White, has written to Siptu to tell them that former Aer Lingus employees, now working with SR Technics, will not be included in the supplementary pension scheme. In a letter, Ms White says, following receipt of legal advice, the decision has been taken not to include this group.

About 600 SR Technics staff want to be included in the supplementary fund. Many of them hold letters of comfort that give them certain entitlements similar to those of current Aer Lingus staff. Ms White writes: "Aer Lingus has no liability with regard to pension claims by this group."

The civil aviation branch of Siptu has written its own letter in recent days to the Dublin Airport Authority about its pension obligations.

The branch wants €100 million from the recent Great Southern Hotel sale to be used to set up a supplementary fund for Dublin Airport Authority staff.