Aviation safety investigations & reports

Traffic alert and collision avoidance system, Resolution Advisory, WA

Investigation number:
200602115
Status: Completed
Investigation completed

Summary

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On 19 April 2006, a Fairchild Industries Inc SA227-DC (Metro) aircraft was being operated from Newman, WA to Perth, WA at flight level (FL) 200. A Boeing Company 717-200 (717) was being operated from Karratha, WA to Perth at FL320. Both aircraft were in controlled airspace and were on tracks that converged.

The crew of the 717 had been provided with a clearance to descend to FL210 by the air traffic controller managing the airspace the aircraft were operating in. This level provided the required minimum vertical separation standard of 1,000 ft with the Metro.

As the crew of the 717 were approaching FL225 the traffic alert and collision avoidance system (TCAS) provided a traffic advisory relating to the Metro. A few seconds later the crew received a TCAS 'reduce descent rate' resolution advisory (RA). The crew advised the controller 'we've got a TCAS resolution advisory we're leaving F210 on descent'. The controller responded by instructing the crew of the 717 to maintain FL210.

Later analysis of Airservices Australia recorded radar data and audio recordings demonstrated that the crew of the 717 had descended to, and maintained, FL210. There was no infringement of separation standards.

The crew of the 717 maintained a high rate of descent approaching their assigned level, which resulted in the TCAS 'reduce descent rate' resolution advisory. The controller did not recognise the rate of descent of the 717, together with the relative positions of the two aircraft, may have generated a RA.

Download Final Report
[Download  PDF: 152KB]
 
 
 
General details
Date: 19 April 2006   Investigation status: Completed  
Time: 1939 WST    
Location   (show map): 9km NW TASKA (IFR)    
State: Western Australia   Occurrence type: ACAS warning  
Release date: 16 November 2006   Occurrence category: Incident  
Report status: Final   Highest injury level: None  

Aircraft 1 details

Aircraft 1 details
Aircraft manufacturer The Boeing Company  
Aircraft model 717  
Aircraft registration VH-NXF  
Serial number 55001  
Type of operation Air Transport High Capacity  
Damage to aircraft Nil  
Departure point Karratha, WA  
Departure time NK  
Destination Perth, WA  
Crew details
Role Class of licence Hours on type Hours total
Pilot-in-Command Unknown

Aircraft 2 details

Aircraft 2 details
Aircraft manufacturer Fairchild Industries Inc  
Aircraft model SA227  
Aircraft registration VH-WBA  
Serial number DC-883B  
Type of operation Charter  
Damage to aircraft Nil  
Departure point Mt Newman, WA  
Departure time 1735  
Destination Perth, WA  
Crew details
Role Class of licence Hours on type Hours total
Pilot-in-Command Unknown
Last update 18 April 2018