Loss of separation involving a Boeing 747-438, Unknown, Zamboanga VOR, on 19 August 1996

An Australian-registered B747 was maintaining flight level (FL) 350 on a flight from Sydney to Hong Kong and was approaching the Zamboanga very high frequency omni-directional radio range beacon (VOR). The crew received a traffic alert and collision avoidance system (TCAS) traffic information advice on an unidentified aircraft at the same level, crossing from right to left and also converging on the Zamboanga VOR. The crew of the B747 initiated a right turn that ensured that their aircraft would pass behind the other aircraft. There was a breakdown of separation.

Investigation by the Bureau in conjunction with the Air Transportation Office of the Republic of the Philippines, established that the other aircraft was foreign-registered and that the crew of that aircraft had been instructed by Manila air traffic control to climb to FL 370 for separation with the Australian aircraft. The instruction had been correctly acknowledged by the crew at the second attempt. The instruction included an authorisation to descend back to FL 350 when 5 minutes past the Zamboanga VOR.

Manila air traffic control had taken all necessary action to ensure positive separation of the two aircraft. The reason why the foreign-registered aircraft was not at FL 370 when passing the Zamboanga VOR could not to be determined.

The crossing point of the two air routes at Zamboanga was not under radar surveillance at the time of the occurrence. However, as part of the improvement to the air traffic system by the Government of the Philippines, a new radar head was commissioned late in 1996 and now provides coverage in this area.