The problem is that most final salary pension fund closed many years ago, so there are not enough contributors to meet the those already, and soon to be retired. Pension funds are also highly dependent on the stockmarket and dividend income. This makes dividends a 2 edged sword, Pension fund need to benefit from them and it leaves Companies with less to fund their own schemes. A lot have moved into safer investments with lower returns.
Many years ago, whilst still working I attended a breakfast meeting (yuk) where the speaker was an Economist. One question was how are pension funds valued. The reply, how many people are their being paid pensions, how many future pensioners will they be, how many will carry on to retirement age contributing and how many will leave the Company. Then work out how long they are all going to live. Stick your finger in the air and see which way the winds blowing. At least he raised a laugh.
Coincidentally I have just closed an email from my own pension provider with the results of the Compulsory Triannual valuation (end of 2014 as it takes so long) It is valued at 102% so at the moment I am hopefully in a fairly secure position.