While complying with the commands of a TCAS RA with and unknown aircraft the flight crew of an hs-12...

Attributes
ACN	955455
Time
Date	201106
Local Time Of Day	1201-1800
Place
Locale Reference	ZID.ARTCC
State Reference	IN
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	HS 125 Series
Operating Under FAR Part	Part 91
Flight Phase	Initial Approach
Route In Use	Vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	Initial Approach
Person 1
Function	First Officer Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 100 Flight Crew Total 4700 Flight Crew Type 1000
Events
Anomaly	Conflict NMAC Deviation - Altitude Excursion From Assigned Altitude
Miss Distance	Horizontal 300 Vertical 0

Narrative:

We were descending on a VFR day into bak; number three for the approach to runway 23. While being vectored to the ILS we received an RA to descend. After reducing the thrust levers to idle and verifying the green area on the vsi; I executed a descent from our assigned altitude of 4;000 MSL to 3;000 MSL. During this time the captain advised ATC that we were responding to a RA. ATC then issued a vector to a heading of 320 while in the descent. While making the turn I spotted a light single engine t- tail trainer. The relative position of the second aircraft was on a 320 heading. This would have put the aircraft at our 12 o'clock position and at the same altitude. I stopped the turn prior to reaching the 320 degree heading. The two aircraft passed within approximately 100 yards of one another. After clear of both conflicts; we visual conducted a visual approach to runway 23 with no further incident. I do not believe there was any way to prevent the chain of events leading to this situation. The second aircraft apparently did not have an operating transponder.

Original NASA ASRS Text

Title: While complying with the commands of a TCAS RA with and unknown aircraft the flight crew of an HS-125 complied with a changed heading clearance from ATC which resulted in an NMAC with a third aircraft.

Narrative: We were descending on a VFR day into BAK; number three for the approach to Runway 23. While being vectored to the ILS we received an RA to descend. After reducing the thrust levers to idle and verifying the green area on the VSI; I executed a descent from our assigned altitude of 4;000 MSL to 3;000 MSL. During this time the Captain advised ATC that we were responding to a RA. ATC then issued a vector to a heading of 320 while in the descent. While making the turn I spotted a light single engine T- tail trainer. The relative position of the second aircraft was on a 320 heading. This would have put the aircraft at our 12 o'clock position and at the same altitude. I stopped the turn prior to reaching the 320 degree heading. The two aircraft passed within approximately 100 yards of one another. After clear of both conflicts; we visual conducted a visual approach to Runway 23 with no further incident. I do not believe there was any way to prevent the chain of events leading to this situation. The second aircraft apparently did not have an operating transponder.

Data retrieved from NASA's ASRS site as of April 2012 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.

While complying with the commands of a TCAS RA with and unknown aircraft the flight crew of an hs-125 complied with a changed heading clearance from ATC which resulted in an near midair collision with a third aircraft.