Wirelessly posted (Opera/9.80 (iPhone; Opera Mini/7.0.2/28.2075; U; en) Presto/2.8.119 Version/11.10)

One use of this may be as a help to getting a LHR-SYD 241. Book the LHR-SYD as soon as it comes up. On your desired return date either phone and add the SYD-LHR leg if available ... but if not, just add HKG-LHR to the 241 (usually available at this stage). Then get the SYD-HKG leg as a separate redemption - a few more miles, but allows a lot more flexibility / availability.