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CIRCUMSTANCES: "A Boeing 747 (B747) operating a scheduled regular public transport flight from Singapore to Melbourne and a Boeing 767 (B767) operating a scheduled regular public transport flight from Perth to Auckland were involved in an alleged close proximity incident near Narrandera NSW. Due to staff shortages in the Melbourne Area Approach Control Centre (AACC) the Melbourne Sector 4 airspace was declared to be deactivated by the issue of a Notice To Airmen (NOTAM) 1523. Whilst this airspace was deactivated transiting aircraft were required to comply with Traffic Information Broadcast Area (TIBA) procedures specified by NOTAM 1522. The B767 flight path would transit this airspace during the period of deactivation. The B747 was offered route shortening at a non-standard level of Flight Level 37 000 feet (FL370) within Sydney controlled airspace under the jurisdiction of the Sydney Area Approach Control Centre Sector 6. The non-standard level was assigned due to other international traffic inbound to Sydney operating below the B747. No positive information update had been provided to the Sector 6 controller about the progress of the B767. Flight paths of both aircraft were within radar surveillance range and jurisdiction of the Sydney Sector 6 controller for some time prior to the incident. The shortened route would place the B747 on a track which would cross that of the B767 at the same level and approximate time near Narrandera unless some separation action was taken. The B767 subsequently entered Sydney Sector 6 airspace three minutes earlier than flight planned estimates indicated. As soon as that aircraft contacted Sector 6 it was instructed to descend from FL370 to non standard level FL350 to provide vertical separation with the crossing B747. The aircraft queried the instruction which was verified by Sector 6. However communications with the aircraft were then lost and no readback of the asigned level was received. Because of this the Sector 6 controller then instructed the B747 to change heading intended to maintain separation and to eventually pass behind the B767. ZK-NBE (B767) The B767 flight plan was submitted at Perth at 1438 Coordinated Universal Time (UTC) for a flight from Perth to Auckland via waypoints overhead Adelaide and Sydney. The flight would transit deactivated airspace promulgated in Melbourne NOTAM 1523 at 0848UTC. This airspace was normally under the jurisdiction of Melbourne AACC Sector 4. The B767 would then enter airspace under the jurisdiction of Sydney AACC Sector 6 at Narrandera. The flight plan Estimated Time of Departure (ETD) was 1530UTC with the associated Estimated Time Intervals (ETI) and Estimated Times of Arrival (ETA) providing en-route timings for the following coded waypoints ETI to MALIM 02.51 - ETA 18.21UTC NYA 02.58 - 18.28 ASSS 03.05 - 18.35 NAR 03.17 - 18.47 RUG 03.31 - 19.01 Once the departure message was received from Perth notifying the actual departure time as 1542UTC (12 minutes later than flight planned) the above estimates could then have been updated as follows ETI to MALIM 02.51 - ETA 18.33UTC NYA 02.58 - 18.40 ASSS 03.05 - 18.47 NAR 03.17 - 18.59 RUG 03.31 - 19.13 This could have given Sydney Sector 6 some expectation that the B767 would enter the deactivated airspace at 1828UTC (prior to MALIM waypoint) and exit deactivated airspace at NAR at 1859UTC. Because of the deactivation of Melbourne airspace the normal step-by-step co-ordination exchanges between the Adelaide Melbourne and Sydney controllers were not completed and the Narrandera strip and estimate could therefore not be accurately updated by the Sector 6 controller. The last actual reported position of the B767 was to Adelaide control at 1748UTC when the aircraft reported over waypoint T6B 1747UTC FL370 estimating MALIM waypoint at 1830UTC; ie. three minutes earlier than could have been expected by the Sydney Sector 6 controller. VH-EBU (B747) The B747 flight plan was submitted in Singapore at 1132UTC for a flight from Singapore to Melbourne via waypoints overhead Derby Parkes Bindook (near Katoomba) Shellys (near Goulburn) and Eildon Weir. This circuitous route was planned to keep the aircraft within controlled airspace and clear of the Melbourne deactivated airspace which had been notified at 0856UTC (Melbourne NOTAM 1523). The aircraft had planned to descend from FL370 to the standard level of FL350 after passing Bindook and tracking towards Shellys and onwards to Melbourne. The aircraft departed within a few minutes of the notified ETD of 1215UTC and proceeded as planned. Subsequently at 1808UTC Adelaide control instructed the B747 to contact Sydney control on Very High Frequency (VHF) 128.2 Megahertz (MHz) at the next waypoint T34A. (At 1812UTC Adelaide control instructed another international aircraft also to contact Sydney control on 128.2 MHz as primary frequency but offered 118.5 MHz as a secondary (alternative) frequency). The B747 contacted Sydney control on 128.2 MHz at 1813UTC and reported passing waypoint T34A maintaining FL370 and estimating Parkes at 1849UTC. At 1836UTC Sydney control Sector 6 advised Melbourne control Sector 2 of the B747 inbound via Parkes and requested if a shorter track from Parkes to Wagga and Melbourne would be available in the Melbourne airspace. Melbourne control analysed the situation and concurred that the B747 could be given amended clearance to track Parkes Wagga Albury Eildon Weir Kinglake and Epping. At 1838UTC Sydney Sector 6 passed this amended clearance to the B747. Then the B747 was given a frequency change from 128.2 MHz to 118.5 MHz to maintain continuous communications for the amended route. Investigation Summary Investigations indicated that the crew of the B767 were given the Melbourne NOTAMs 1522 and 1523 on the flight deck just prior to departure from Perth. They did not consider that there had been a breakdown of separation resulting from the incident. The B767 crew considered that the incident had been resolved as a Sydney control supervisor had spent some time discussing the matter on air with them. They acknowledged that they had the appropriate NOTAMs but had not fully understood the significance of Para.7 of NOTAM 1522. The B767 crew believed that their clearance from Perth via planned route was valid through all Australian airspace and that the wording of Para 7 ""SHOULD"" was not a mandatory requirement even though they had been advised of the frequency by Adelaide as 128.2 MHz. It should be noted that the VHF site for the 128.2 MHz facility is at Mt Oxley approximately 260 nautical miles north of Narrandera near Bourke. As VHF communications are restricted to line of sight propagation characteristics the use of this frequency placed the B767 at the limit for communications over this distance at FL370 and out of communications at FL350. The crew of the B767 were using Jeppesen charts which similar to the Australian documentation carried ambiguous frequency data indicating that the choice of frequencies to be used in the Trans Continental Control Area (TCTA) and Western Routes (from Sydney) were 128.2 MHz or 118.5 Mhz when beyond 150 nautical miles Sydney. Whereas the latter frequency was the correct frequency to be used in the Southern portion of Sector 6 airspace. The 118.5 MHz VHF facility site is located at Mt Canobolas near Orange almost on the direct track and only 130 nautical miles from Narrandera. The B767 crew had made all the required broadcasts on the TIBA frequency 128.95 MHz whilst within deactivated airspace. They first became aware that the event had been reported as an incident when they heard it from the media after arrival at Auckland. Investigation of the incident indicated the following . the Sector 6 controller had no co-ordination update provided for the Narrandera waypoint . the flight progress strip ETA Narrandera was correctly based on ATD . the Sector 6 controller was unable to descend the B747 due to other crossing traffic . an SSR return was observed in the vicinity of Narrandera indicating FL370 which was believed to be the B767 . the Sector 6 controller could not determine the frequency used by the B767 on first contact because of the placement and operation of the VHF control and presentation facilities on controller workstations . the B767 did not respond to the level change instruction and the level readout display was slow to indicate a descent had been initiated . the Sector 6 controller was not permitted to use the Mode C level readout for separation purposes . the Sector 6 controller discussed the situation with more senior controllers and elected to turn the B747 right of track to avoid crossing the flight path of the B767 . radar separation standards were maintained at all times . the aircraft had vertical separation of 2000 feet at the time of passing . the B767 had not called 15 minutes prior to entering Sydney airspace for clearance in accordance with TIBA NOTAM procedures The investigation concluded that there was no breakdown of the prescribed separation standards and that although both aircraft had not been formally identified on radar there was sufficient information for the Sydney Sector 6 controller to anticipate that the aircraft painting over Narrandera at FL370 was the B767. The off-airway route shortening of the B747 initiated by air traffic control added complexity to the prevailing traffic airspace management and co-ordination requirements. The investigation noted that at the time that the B767 first made contact with Sydney Sector 6 on 128.2 MHz the VHF transmission was very broken. This can be indicative of an aircraft either with transmitter problems or on the extreme range of VHF communications. On the first communication Sector 6 instructed the B767 to descend to non-standard level FL350. This was intended to maintain vertical separation between the B767 and the crossing B747. The VHF reception of Sector 6 by the B767 was also most probably broken for the same reason (ie equipment problems or out of range) and the B767 aircrew queried that instruction. Sydney Sector 6 verified the instruction and added that the aircraft was required to report reaching FL350. There was no response to this instruction or readback of the new assigned level by the B767. This was most probably because it was then out of range of the Mt Oxley VHF facility even at FL370. Loss of communications with the B767 left the Sydney Sector 6 controller with minimal options to maintain separation between the B747 and the B767. The chosen action was to vector the B747 away from the flight path of the B767. Sydney Sector 6 contacted the B747 thirty seconds later and instructed that aircraft to turn right onto a magnetic compass heading of 270 degrees for separation purposes. Sector 6 continued to call the B767. When no contact could be established the B747 was given traffic information with the relative bearing (2 o'clock) and distance (30nm) from the B767 with the advice that the aircraft was out of communications at that time. The B747 reported sighting the B767 traffic. Subsequently at the time of passing (1900.30UTC by radar plot) the aircraft were separated by 10.5nm horizontally travelling in opposite directions and achieving 2000ft vertical separation. Sydney Sector 6 continued to call the B767 until communications were established on 118.5 MHz at 1901.40UTC some 4 minutes 20 seconds after contact was lost at 1857.20UTC. The B767 then reported maintaining FL350. At that time the aircraft was 2000 feet below and 17 nm from the B747 and increasing the horizontal separation. The investigation also revealed that the crew of the B767 and the Air Traffic Service staff did not fully understand the intentions and procedures expressed in the appropriate Melbourne NOTAMs. This is not a reflection of the comprehension skills of the personnel but an indictment of the complexity and ambiguity of the NOTAMs and the procedures." RECCOMENDATIONS: "It is requested that the Civil Aviation Authority give consideration to the following recommendations to ensure that air traffic control personnel 1. Use consistent phraseology when initiating frequency change instructions. 2. Issue the correct frequency change instruction for the area in which an aircraft is or will be operating. 3. Are reminded of the necessity to accomplish frequency changes before an aircraft is out of VHF range from the previous VHF outlet. 4. Are provided with documentary evidence of the VHF coverages available from the outlets under their control. 5. Are provided with training in VHF communications characteristics of the CAA radio telephony systems. 6. Have the control and presentation of the VHF/UHF frequency call lights modified so that controllers can immediately determine the frequency on which an aircraft is calling. 7. Have procedures prescribed to indicate the frequency coded if necessary on which an aircraft is communicating and all subsequent frequencies recorded on the flight progress strip applicable to a particular controller where more than one frequency is terminated at that workstation. 8. Be advised of this incident as an example of where the offering of track shortening and non standard levels can result not only in increased communications control workloads and co-ordination but may suddenly and unexpectedly result in reduced safety standards."
Download Final Report
[ Download PDF: 7.73MB]
General details
Date: 29 April 1989 Investigation status: Completed 
Time: 4:59 EST  
 Investigation type: Occurrence Investigation 
Release date: 30 August 1990 Occurrence class: Infrastructure 
Report status: Final Occurrence category: Incident 
Aircraft 1 details
Aircraft manufacturer: The Boeing Company 
Aircraft model: 747 
Aircraft registration: VH-EBU 
Sector: Jet 
Departure point:Singapore
Aircraft 2 details
Aircraft manufacturer: The Boeing Company 
Aircraft model: 767-300 
Aircraft registration: ZK-NBE 
Sector: Jet 
Damage to aircraft: Nil 
Departure point:ADELAIDE SA
Destination:AUCKLAND NZ
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