If you read the ATSB report:
The crew had briefed the new transition level at top of descent and had briefly discussed the need
to conduct the approach checklist on passing through the transition level when they were
descending through FL 130 (the usual transition level). The crew had put a plan in place to
complete the checklist. However, as they were flying over the non-directional beacon at FL 050
and were looking at the runway in preparation for the commencement of the approach, workload
began to rise and they forgot to return to the approach checklist and complete it, as per a
prospective memory error.