I flew out of Los Angeles in July 1990 in a very full 747-211B , G-GLYN. The take off roll seemed very protracted but we got away OK and had a reasonable flight back to Gatwick. Although it was a BA flight, the aircraft had been owned by BCal and had spent some time in the desert being stored between ownerships. Talking to an ex BCal captain (Mike Graty anybody?) he claimed that when it was "opened up" for a major service BA found a noticeable amount of "Mojave" sand in it which helped explain the poor fuel consumption and takeoff performance..Not sure how true this was but BA didn't keep it very long.