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The crew of a Saab 340 were arriving at Sydney from the north-west and had been cleared by air traffic control to make a visual approach to runway 16R. The controlled airspace steps in that sector required the crew to maintain an altitude of 2,500ft until 12 NM, when further descent would be available. As they were passing through 2,400ft, they observed an airship immediately in front and below. The aircraft's traffic alert and collision-avoidance system (TCAS) issued a Resolution Advisory alert and the crew reduced the rate of descent until they had passed the airship.

The airship had been tracking outside controlled airspace at a planned altitude of 1,500ft and was being navigated along the boundary of that airspace which, at that point, was a 12 NM arc based on Sydney airport. The crew was required to remain north-west of that boundary.

Analysis of the recorded data indicated that the airship had marginally infringed controlled airspace and was 11.9 NM from Sydney. The Saab 340 had descended marginally through the 2,500ft limit and was approximately 2,300ft when it passed the airship.

The TCAS actuated based on the reducing altitude differential and provided the crew with timely information on the airship below it.

General details
Date: 16 July 2000 Investigation status: Completed 
Time: 1623 hours EST  
Location   (show map):13 km NNW Sydney, Aero. Investigation type: Occurrence Investigation 
State: New South Wales  
Release date: 24 October 2001  
Report status: Final Occurrence category: Incident 
 Highest injury level: None 
Aircraft details
Aircraft manufacturer: S.A.A.B. Aircraft Co 
Aircraft model: 340 
Aircraft registration: VH-KDQ 
Serial number: 340B-325 
Type of operation: Air Transport Low Capacity 
Damage to aircraft: Nil 
Departure point:Canberra, ACT
Destination:Sydney, NSW
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Last update 13 May 2014