Last night I read the report from 1997 of the UA 747 HRT-HNL that hit turbulance and there was one fatality. A common element was: We are very close to Fiji on the map when there appears to be a low frequency (around 1sec) up and down motion. The seat belt sign is off. The captain of that flight reported an low frequency ocilation in altitude of about 50 feet just before the incident. Beware!