Large transport aircraft being vectored for approach to bfi; responded to a TCAS RA and experienced ...

Attributes
ACN	1020881
Time
Date	201207
Local Time Of Day	1801-2400
Place
Locale Reference	S46.TRACON
State Reference	WA
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Widebody Low Wing 2 Turbojet Eng
Flight Phase	Final Approach
Route In Use	Vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	Final Approach
Component
Aircraft Component	Transponder
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Conflict NMAC
Miss Distance	Horizontal 100 Vertical 100

Narrative:

We were on a vector for 13R approach to bfi; configured flaps 1; speed 190 KTS with sea approach when an unidentified aircraft appeared on TCAS 2.5 miles ahead. Approach had just given us a vector towards this 'pop-up TCAS target at our altitude' and we queried approach if they were aware of the traffic. At that moment an unidentified voice on the radio said; 'I just turned on my transponder.' at that moment TCAS advised to monitor vertical speed then told us to 'climb; climb' and the co-pilot immediately disengaged the automation and followed the TCAS vsi out of the red arc while simultaneously applying full power. I immediately notified ATC we were in a TCAS climb. After passing over the aircraft at approximately 100-200 ft (according to the TCAS readout); TCAS announced we were 'clear of conflict' and we advised ATC who re-cleared us to our original vector and altitude for the approach.

Original NASA ASRS Text

Title: Large transport aircraft being vectored for approach to BFI; responded to a TCAS RA and experienced an NMAC with 'pop-up' traffic that had just activated the aircraft's transponder.

Narrative: We were on a vector for 13R approach to BFI; configured Flaps 1; speed 190 KTS with SEA approach when an unidentified aircraft appeared on TCAS 2.5 miles ahead. Approach had just given us a vector towards this 'pop-up TCAS target at our altitude' and we queried Approach if they were aware of the traffic. At that moment an unidentified voice on the radio said; 'I just turned on my transponder.' At that moment TCAS advised to monitor vertical speed then told us to 'Climb; Climb' and the Co-Pilot immediately disengaged the automation and followed the TCAS VSI out of the red arc while simultaneously applying full power. I immediately notified ATC we were in a TCAS climb. After passing over the aircraft at approximately 100-200 FT (according to the TCAS readout); TCAS announced we were 'Clear of Conflict' and we advised ATC who re-cleared us to our original vector and altitude for the approach.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Large transport aircraft being vectored for approach to bfi; responded to a TCAS RA and experienced an near midair collision with 'pop-up' traffic that had just activated the aircraft's transponder.