Originally Posted by
ashill
Not to mention that IAD-LHR-XXX and BWI-LHR-XXX are options for WAS-Europe that weren't possible on pmUS, which reduces the need to funnel WAS-Europe traffic through PHL.
Two big advantages of WAS-PHL-Europe over WAS-LHR-XXX is avoiding a connection in LHR, and only having to go through airport security once instead of twice.