QANTAS Boeing 737-838 VH-VYA operated QF1078 Brisbane – Mount Isa this afternoon but was unable to operate the return QF1079 due to a technical issue. Sister VH-VZC positioned Brisbane – Mount Isa as QF6122 in order to operate the delayed QF1079. VH-VYA was able to position Mount Isa –Brisbane very late in the evening.