Originally Posted by
WHBM
Not generally known is the long loop from T4 going on round to T123 does swing right round westwards and underneath T5 (it passes under the taxiway between T5B and T5C). Furthermore, when built in 1984, a straight section was provided for a possible future platform, just in case a T5 was built here
Based on the map I've seen, the loop does go a fair way westwards but nowhere near the main T5 building. It passes between taxiways D and E, where T5D may be built in the future, well east of T5C.