Complex sentence: At 1909:20 VH-AAV was cleared to land, however this clearance was not acknowledged as at 1909:22 the aircraft impacted the sea wall six feet above the waterline.
Split into simpler sentences: At 1909:20 VH-AAV was cleared to land but this clearance was not acknowledged. At 1909:22 the aircraft impacted the sea wall six feet above the waterline.