Alex you are right about BA getting its sums wrong, I was the POC in MOD for the initial Tristar operations and worked closely with BA on crewing, catering etc when we were hiring BA crews. Interestingly the BA Tristar 500s had been upgraded by Lockheed with active flying controls and other mods as they would not achieve the stated payload/range which was based on the London Vancouver sector. They were therefore probably the longest range Tristars ever built and we put them into use on sectors such as BZZ-Nairobi and BZZ-Calgary as well as the ASI and then FI run where they were capable of moving 300 pax. The savings achieved were significant as we could replace 2 VC10s operating over 2 days with a single Tristar taking one day moving more pax. As a result I started the campaign to retain at least one unmodified Tristar for pax as a cost savings measure which was ultimately successful. I believe that BA also rued the decision to get rid of these aircraft as within a few months of selling them to the RAF they were chartering less capable Air Lanka Tristars to operate some of their South American routes.