* * * * * root su apache -c "/usr/bin/php /var/www/html/timetrex/maint/cron.php" > /dev/null 2>&1
just make sure that the cron.php file is executable by the user you switch too!!!
Segfaults in PHP are really crappy to deal with....it could be hardware related (we have definitely had support tickets where this was the issue and resolved completely by swapping out memory), but in the old 5.x we also had seg faults because of the IMAP client libraries used...Although the mail archive in V6 makes less use of the PHP libraries for IMAP, it could still be cropping up in some cases.
As mentioned at the beginning, tracking it down is labour intensive task.
Maybe it's time to look at using an alternative. I'll add it to the bug tracker, but no promises on timeline.