thank you for asking the question I have wanted to for ages!
interestingly enough, the only place
I have noticed them is on the Boeing fleet, 73s and 77s.
try out:
http://www.!!!!!!!!!!!!!!/open.file?id=1190624&size=L
and
http://www.!!!!!!!!!!!!!!/open.file?id=0765848&size=L
I thunk thuuur puuuuurdy