John Hill
A BEA Vanguard G-APEC suffered a failure of its rear pressure bulkhead caused by corrosion on 2 Oct 71 over Belgium. It lost a major part of its tail and the crew used the R/T on the way down to make a mayday call saying they were falling - which to me is a sure sign that they realised they could do nothing more.
I seem to remember that at the time it was felt that nicotine and or lavatory chemicals had caused the corrosion. Several other Vanguards were found to have similar - although less severe corrosion.
JF