Aviation safety investigations & reports

Boeing Co 737-377, VH-CZE

Investigation number:
Status: Completed
Investigation completed


A Boeing 747 (B747) had departed Avalon, Victoria on a track that passed over Melbourne and then to the northeast. The crew had been issued with a requirement to initially maintain flight level (FL)200. The departures controller had imposed the limitation in accordance with standard operating procedures that required the "cap" to be placed on all aircraft that had planned to a higher flight level. Airspace above FL200 was under the jurisdiction of a sector controller. In addition, the horizontal boundary between the two controllers' airspace below FL200, was 30NM from Melbourne airport.

The departures controller had a Piper Navajo aircraft tracking ahead of a sequence of three jet aircraft departing from Melbourne airport. That situation required that the jet aircraft be radar vectored around the slower aircraft before they could be placed on their flight planned tracks. The first of the jet aircraft was a Boeing 737 (B737) for Brisbane, which departed approximately the same time as the B747.

The tracks of the aircraft were such that the B737 was initially to the left of the B747, but at approximately 30NM northeast of Melbourne they crossed and thereafter diverged.

The sector controller had noticed that the B747 would probably reach FL200 while still in departures airspace and, as a consequence, be forced to maintain FL200. In order to provide the crew of the B747 with an unrestricted climb profile, he coordinated with the departures controller to authorise the crew of the B747 to climb to FL370.

At that time, the B737 was below and approximately 30NM ahead of the B747. However, the ground speed of the B747 was approximately 70 knots faster than the B737, and the B737 had a greater rate of climb.

As the B737 approached the horizontal airspace boundary, the departures contoller handed over the aircraft to the sector controller while it was passing FL170. The sector controller then approved the crew to climb to FL370, as he believed there was sufficient distance between the aircraft to maintain separation. A short time later, the B747 was also handed over to the sector controller as it was passing FL200 and approximately 8 NM behind the B737. At that moment, The Australian Advanced Air Traffic Control System (TAAATS) Short Term Conflict Alert (STCA) activated and the controllers immediately attempted to prevent an infringement of separation standards. However, the crew of the B747 was on his frequency and asked the departures controller to maintain that aircraft at a lower level. The departures controller issued an instruction for the crew of the B737 to maintain FL190 but did not receive a reply, because that crew was on the sector frequency as instructed.

At that moment, the crew of the B747 made radio contact with the sector controller who immediately issued an instruction for them to turn the aircraft. There was a delay as the crew questioned the instruction, but they commenced the manoeuvre when the controller issued the instruction a second time using the word "immediately". He then instructed the crew of the B737 to level out, which they did.

The aircraft passed approximately 2.5NM apart while the vertical separation standard of 1,000ft did not exist. The required radar separation standard was 5 NM.


The STCA activation would have provided sufficient warning for the subsequent actions to have prevented an infringement of separation standards. However, the delay caused by the transfer of radio frequency by the crew of the B747 and the sector controller forgetting that the crew of the B737 was on his frequency, exacerbated the situation and led to a delay in the effect of the instructions.

Neither controller realised that a significant closing speed existed and that they had not provided adequate separation assurance. Although the responsibility for separation during the transfer of control responsibility was primarily with the departures controller, the reason why the controllers did not provide separation assurance could not be determined.

Significant Factors

  1. Neither controller realised that there was a significant closing speed between the aircraft.
  2. Neither controller applied the principles of separation assurance.
General details
Date: 25 February 2001   Investigation status: Completed  
Time: 1022 hours ESuT    
Location   (show map): 46 km N Melbourne, Aero.    
State: Victoria   Occurrence type: Loss of separation  
Release date: 05 February 2002   Occurrence category: Incident  
Report status: Final   Highest injury level: None  

Aircraft 1 details

Aircraft 1 details
Aircraft manufacturer The Boeing Company  
Aircraft model 737  
Aircraft registration VH-CZE  
Serial number 23657  
Type of operation Air Transport High Capacity  
Damage to aircraft Nil  
Departure point Melbourne, VIC  
Destination Brisbane, QLD  

Aircraft 2 details

Aircraft 2 details
Aircraft manufacturer The Boeing Company  
Aircraft model 747  
Aircraft registration IDEMR  
Type of operation Air Transport High Capacity  
Damage to aircraft Nil  
Departure point Avalon, VIC  
Destination Osaka, JAPAN  
Last update 13 May 2014