PIA 747-100s had a bit of history at LHR as I recall, one losing an engine depating to the east and really struggling over Heston Hounslow Acton area -Iseem to recall there was beacon at Kilburn in those days that easterly depatures to N and East passed over .
Going the other way , and I may be mistaken about PIA here, buit a 747 off the 28/27s lost an engine on take off and seriously struggled to get over Surrey Hill to the NE of Camberley- topped with a 300+ foot high BT tower too.
others may have clearer recollection of these events but back in the day 'low flying' aircraft were not uncommon, and thats without aged piston props that really did need the curvature of the earth to climb and a clearway of about 20 miles -well sort of