opatch is not in the $PATH in EBS R12.1.1

For some reason, opatch is not part of $PATH variable.  It is missing from the $CONTEXT_NAME.env file under $INST_TOP/ora/10.1.2:

$ opatch lsinventory

-ksh: opatch: not found [No such file or directory]

$ cd $INST_TOP/ora/10.1.2

$ grep OPatch *.env    <== Normally, it should display one line. But nothing here.

I ran autoconfig, and the problem still exists.  What It may be wrong? Where can I fix it?

Thank you.