I was at an outdoor birthday celebration at 1553 Albany Highway Beckenham. The children were looking at the stars and picking out the bright ones. When lights were first noticed I thought it was a domestic airplane flying at a very high altitude,such as intercontinental flights. There were three lights grouped something like navigation lights on a commercial airplane but much larger and brighter than normal aircraft navigation lights.The lights were flashing at roughly the same rate as normal aircraft. Lights were moving from south to north at about the same speed as an airplane at high altitude.When about directly above lights made sharp turn to head in a westerly direction. After traveling west for about 30 seconds they disappeared. A commercial airplane landed at Perth airport at the same time so I could see both at the same time. I feel it classifies as a UFO because its altitude,right angle change of direction and sudden disappearance. It has aroused my curiosity and would really like to know what it was or could have been.