Air carrier given clearance to descend does not because of a TCASII RA for traffic unknown to contro...

Attributes
ACN	447569
Time
Date	199908
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : ind.airport
State Reference	IN
Altitude	msl single value : 10000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ind.tracon
Operator	common carrier : air carrier
Make Model Name	B727 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Route In Use	approach : instrument precision arrival other
Flight Plan	IFR
Aircraft 2
Operator	Other
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 100 flight time total : 6000 flight time type : 2000
ASRS Report	447569
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : multi engine
Events
Anomaly	conflict : airborne critical conflict : nmac non adherence : clearance other anomaly other
Independent Detector	aircraft equipment : tcas other flight crewa other flight crewb
Resolutory Action	flight crew : took evasive action
Miss Distance	horizontal : 0 vertical : 400
Supplementary
Problem Areas	Company Flight Crew Human Performance Airspace Structure
Primary Problem	Airspace Structure

Narrative:

We were flying directly to an IAF for runway 5L at ind expecting a visual approach. We were cleared to 9000 ft. Approach control pointed out IFR traffic at 2 O'clock and 8 or so mi at 8000 ft. We saw this target on TCASII. I leveled at 10000 ft to slow when another target appeared at 9500 ft in close proximity to the 8000 ft IFR traffic. We were converging with both targets so I stayed at 10000 ft. The 9500 ft traffic became a TA. His altitude changed to 9600 ft, approaching us, and became an RA. Although approach control directed us to descend to 9000 ft 2 more times, I stayed at 10000 ft adhering to the RA. My captain saw the 8000 ft traffic, but none of us saw the 9600 ft traffic. After we cleared the conflicting traffic, we continued our descent. Approach said he did not see the 9600 ft traffic. If our aircraft was not equipped with TCASII (most in our fleet are not) we would have had a midair collision).

Original NASA ASRS Text

Title: ACR GIVEN CLRNC TO DSND DOES NOT BECAUSE OF A TCASII RA FOR TFC UNKNOWN TO CTLR.

Narrative: WE WERE FLYING DIRECTLY TO AN IAF FOR RWY 5L AT IND EXPECTING A VISUAL APCH. WE WERE CLRED TO 9000 FT. APCH CTL POINTED OUT IFR TFC AT 2 O'CLOCK AND 8 OR SO MI AT 8000 FT. WE SAW THIS TARGET ON TCASII. I LEVELED AT 10000 FT TO SLOW WHEN ANOTHER TARGET APPEARED AT 9500 FT IN CLOSE PROX TO THE 8000 FT IFR TFC. WE WERE CONVERGING WITH BOTH TARGETS SO I STAYED AT 10000 FT. THE 9500 FT TFC BECAME A TA. HIS ALT CHANGED TO 9600 FT, APCHING US, AND BECAME AN RA. ALTHOUGH APCH CTL DIRECTED US TO DSND TO 9000 FT 2 MORE TIMES, I STAYED AT 10000 FT ADHERING TO THE RA. MY CAPT SAW THE 8000 FT TFC, BUT NONE OF US SAW THE 9600 FT TFC. AFTER WE CLRED THE CONFLICTING TFC, WE CONTINUED OUR DSCNT. APCH SAID HE DID NOT SEE THE 9600 FT TFC. IF OUR ACFT WAS NOT EQUIPPED WITH TCASII (MOST IN OUR FLEET ARE NOT) WE WOULD HAVE HAD A MIDAIR COLLISION).

Data retrieved from NASA's ASRS site as of July 2007 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.

Air carrier given clearance to descend does not because of a TCASII RA for traffic unknown to controller.