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VH-NMA was en route from Perth to Meekatharra at 27,000 feet (FL270) and had passed position Mount Magnet at time 0810 and was estimating Meekatharra at 0831. VH-FMQ departed Readys for Perth at time 0801 and was estimating Mount Magnet at 0819, and had planned at FL260. In addition VH-LBX was en route between Peakhill Mine and Perth. This aircraft had planned via Meekatharra (estimate 0825) and Mount Magnet (estimate 0848). VH-LBX was issued with a requirement to Reach FL240 by Meekatharra to facilitate separation with the other traffic. At time 0813.5 a clearance was issued to the pilot of VH-FMQ to transit via planned route, to climb to FL220, and to expect higher levels at Mount Magnet. At time 0816 an instruction was passed to the pilot of VH-NMA to leave control area on descent with a requirement to reach FL230 by time 0820. This was done to ensure separation with VH-LBX. The pilot of VH-NMA queried the requirement and was told it was due to traffic. VH-NMA then commenced descent. At time 0819.5, the pilot of VH-NMA reported leaving FL230 and requested the traffic. The Perth Sector 4 Controller advised the pilot of VH-NMA that he could expect a short delay at FL230. The pilot queried this, stating he had just left FL220. The Sector 4 Controller then told the pilot of VH-NMA to report leaving FL210. At time 0821, the pilot of VH-FMQ reported passing over Mount Magnet at time 0819, maintaining FL220. The aircraft were now established on opposite sides of a Navaid and adequately separated. The Sector 4 Controller had predetermined how to separate the aircraft involved, but gave the pilot of VH-NMA an instruction to leave control area on descent, instead of limiting decent to FL230 to remain separated from VH-FMQ. Prior to issuing the descent clearance, the Controller did not advise the pilot of VH-NMA of the plan to enable him to descend into Meekatharra without experiencing extensive delays. Had this been done it is likely the pilot of VH-NMA would have realised the error when he was given descent below FL230. VH-FMQ passed over Mount Magnet at time 0819 which was the time that NMA reported leaving FL230, so although separation existed, the Controller was unaware of the fact. The Controller was experienced and, at the time was also performing Team Leader duties. A review of the flight strips indicated that no times of passing between the aircraft were recorded on the flight progress strips and other details missing indicated that the Controller was not performing at the required technical level at the time. The traffic levels in Sector 4 when it is busy, particularly in the vicinity of Mount Magnet, may warrant a separate flight progress board bay designator for Mount Magnet. This would make it much easier to visualise conflictions than the current method where the Mount Magnet position is located adjacent to the Mount Singleton designator. Safety Action The Civil Aviation Authority are reviewing the possible use of a Mount Magent designator on the fllight progress board.
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General details
Date: 23 November 1994 Investigation status: Completed 
Time: 8:20 WST Investigation type: Occurrence Investigation 
 Occurrence type:Loss of separation 
 Occurrence class: Airspace 
Release date: 01 February 1995 Occurrence category: Incident 
Report status: Final  
Aircraft 1 details
Aircraft manufacturer: Cessna Aircraft Company 
Aircraft model: 441 
Aircraft registration: VH-FMQ 
Sector: Turboprop 
Damage to aircraft: Nil 
Departure point:Yardy WA
Destination:Perth WA
Aircraft 2 details
Aircraft manufacturer: Piper Aircraft Corp 
Aircraft model: PA-42 
Aircraft registration: VH-NMA 
Sector: Turboprop 
Damage to aircraft: Nil 
Departure point:Perth WA
Destination:Meekatharra WA
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Last update 21 October 2014