CIRCUMSTANCES VH-AZX, a Beech 76, was taxiing for takeoff at the same time as VH-NJU, a British Aerospace 146. Both aircraft had made the appropriate mandatory broadcast zone (MBZ) calls. While lining up for takeoff, the crew of NJU noticed AZX at taxiway E approaching the runway. The crew of NJU broadcast "rolling" and AZX stopped. Immediately, another voice broadcast that AZX had infringed the flight strip and suggested that the pilot should take off. This broadcast was acknowledged by the pilot of AZX, who taxied onto the runway and took off. The crew of NJU had only just commenced the take off roll and rejected the takeoff. The other voice was that of the airport safety officer, who was in a vehicle near taxiway E. He saw AZX cross the holding point and enter the flight strip. He believed that the crew of NJU had not seen AZX, and that a dangerous situation existed. This was the basis for his radio transmission to the pilot of AZX. The investigation found that there were no published procedures or guidelines for airport safety officers to follow in situations perceived to require immediate action. On this occasion, the safety officer made a radio transmission which the pilot of AZX interpreted as an air traffic control instruction and which he subsequently followed. SAFETY ACTION The Bureau of Air Safety Investigation is currently investigating a perceived safety deficiency that has been identified as a result of this occurrence. The deficiency involves the lack of published information available to airport safety officers on recommended radio usage. This information is necessary in order to provide safety officers with phraseology they can use to alert pilots to safety hazards, without using terms that could be interpreted as controlling or suggesting. Any recommendation issued as a result of this investigation will be published in the Bureau's Quarterly Safety Deficiency Report.