| Incident: TCAS RA's in Control Zone's
The following incident was observed at Christchurch (NZCH) last week:
A 737 was descending to 2000ft on a visual approach, right hand downwind for Runway 20. As the aircraft crossed West Melton airfield at 2000ft, an erroneous transponder indication from a piper cherokee 1000ft below placed a target in front of the 737 at 2300ft.
As a result a TCAS Descent was commanded and the 737 entered uncontrolled airspace at West Melton where there were 3 aircraft in the West Melton circuit.
ENR 1.6 - 10 states:
ACAS procedures
(c) When operating by visual reference within, or entering a controlled
aerodrome traffic circuit, pilots should operate ACAS systems on
Traffic Avoidance (TA) mode. This is to avoid unnecessary Resolution
Advisory (RA) manoeuvres against controlled traffic where visual,
composite visual, 500ft vertical or runway separation standards that
are not considered by ACAS systems are being applied.
What is the accepted airline standard operating procedure for TCAS' in a control zone?
Is there a resistance from some pilots to use TA mode only in high traffic control zones? | 
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