Zones,
normal routing out to HKG oftentakes you across the Khazakstan/Chinese border just south of Mongolia, passing close to Urumqui and then continuing in a loop around the Tibetan plateau until tracking south to HKG.
Safety heights on the route are high (around 19,000 ft I think) but a 744 out of LHR would have a 2 Eng stab height in excess of 20000ft.
Crew call on the day!