A Mitsubishi MU-2B-30 (VH-WMW) was to be flown on a cargo flight from Bankstown to Wagga Wagga, Australia. At the same time another aircraft, Metro II VH-UUK was also to be flown on a cargo flight from Bankstown to Cootamundra, Australia. The MU-2 taxied at 06:30 for runway 29C, followed some three minutes later by the Metro II. The MU-2 proceeded along taxiway X, then across the 29 engine runup area towards taxiway S1, which also required crossing taxiway K. The Metro II proceeded along taxiway K, towards taxiway S1. As he taxied through the runup area the MU-2 pilot was unaware of the presence of the Metro II on taxiway K. The Metro II pilot had seen the MU-2 to his left, taxiing through the runup area, and assumed that the pilot of that aircraft would give way to him. He reported that his attention was mainly directed ahead and to his right, as he monitored departing aircraft. As the MU-2 was turning left out of the runup area to cross taxiway K, the pilot felt a lurch to the left as his aircraft was struck from the rear right. The wing of the Metro II had passed under the right wing tip fuel tank and then into the propeller of the right engine, resulting in substantial damage to both aircraft. The pilot of the Metro II had been unaware of the close proximity of the MU-2 until the impact pulled the nose of his aircraft to the left, and he saw the other aircraft. Both pilots conducted emergency shut-downs and escaped from their aircraft without injury. Pilots of adjacent aircraft witnessed the accident and reported that it was a clear morning with no obstructions to visibility. Immediately prior to impact, the witnesses observed the aircraft to be converging at an angle of approximately 50 degrees and thought it was going to be close. When the impact was seen as inevitable, they were unable to give a warning call as the ground radio frequency was congested.