All oz flights 747 operated, including BA17 which is LHR-SIN-MEL (the SYD bit must be a QF domestic) Furthest east the 777 goes is Beijing. Very unlikely to substitute a 777 to OZ as Singapore based cabin crew not 777 trained for starters. Also 777 is substituting for 767's being refurbished so theres not much slack in the system to lose and aircraft for 2 days (would also require 3 sets of Flight crew to be positioned to SIN/SYD at least 2 days prior to leaving LHR.