we still using old apache version, 1.3.37 to be exact. And today i discovered in its log file:

[Wed Dec 27 18:14:42 2006] [notice] child pid 19870 exit signal Segmentation fault (11)

but i don't found core file to be created. So, i've added CoreDumpDirectory into httpd.conf, but to my surprise, this doesn't help also. googlin a bit, i've found mod_prctl.c which finally helped me to get core files.