CAA staff are not public sector employees in the normal sense of the word. Since it was formed it has been a Government agency and its employees are not civil servants although for some time those who transferred from the Board of Trade were entitled to some of the terms and conditions of civil servants when they were preferable to the CAA ones. They belong to an employee/employer funded pension scheme and are not part of the public sector scheme. Their part of the scheme is no more bullet proof than ours. Eventually their part of the scheme will have the same problem of people living longer than their current contributions can support although for the reasons given by Me Me Me and 250 Kts they won't get there as quickly as the NATS part.
Public sector pensions are funded by current taxpayers not by pension pots so whilst there are enough people paying taxes they aren't subject to the same market conditions. Eventually though the number of pensioners will outweigh the funding available from current taxpayers and at that point they won't be quite so bullet proof.