In the late 1980s I was positioning JER-GCI on a clockwork Tristar with another member of crew,we had the last row just below the engine on the fin.The pilot taxied to the hold on two engines,we naturally expected the third engine to start before TO but no we lined up and powered up and started to roll,we both shouted STOP!! The pilot vacated the runway taxied back to the hold and started the third engine and took off.