"We will continue pursuing the search with much vigour. I have to say in my experience, and I have got a lot of experience in search and rescue over the years, this search and rescue operation is probably the most challenging I have ever seen," the former air chief marshal says in Perth.
"Inevitably, if we don't find wreckage on the surface, we are eventually going to have to - in consultation with everybody who has a stake in this - review what we do next."
DPA