Originally Posted by
SpringHeeledJack
I saw this beast many times back in the day whilst spotting at LHR, but can't say I ever noticed the 'bump' just after the main hump joins the fuselage. What was inside ? These days such protrusions are commonplace, but back then they were somewhat rare.
Photos of several early -100s and -200s with that bump can be found on the Net. The consensus seems to be either Satcom or GPS.
Interestingly, Paddy Zulu and its sister ship lost the bumps a few years after the BA lease.