Large transport in IMC has TCASII RA when cleared for and starting descent. Responds with climb.

Attributes
ACN	271160
Time
Date	199405
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : ard
State Reference	PA
Altitude	msl bound lower : 12400 msl bound upper : 13400
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	MD-88
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	enroute airway : n90
Flight Plan	IFR
Aircraft 2
Operator	general aviation : corporate
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Flight Phase	cruise other
Flight Plan	None
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time total : 10000
ASRS Report	271160
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 180 flight time total : 6000 flight time type : 1500
ASRS Report	271057
Events
Anomaly	conflict : nmac other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 0 vertical : 450
Supplementary
Primary Problem	Flight Crew Human Performance

Narrative:

Cleared to descend from 13000-11000 ft. Started descent to about 12400 when TCASII called 'traffic.' shortly thereafter (5 seconds) TCASII issued RA to climb. Climb was initiated as traffic was showing -- 400 ft on TCASII. By the time a position rate was indicated, the traffic was minus 200 ft. Captain looked out and saw what appeared to be small business jet within 3-4 mi and closing rapidly directly in our flight path. As it passed beneath us, it was 400-500 ft.below. He made no evasive maneuver and appeared not to see us. I informed controller we were climbing as directed by TCASII, he said he had no traffic in our area. Later he called back and said he had not seen the traffic which caused the conflict. We climbed to 13400 before again commencing descent. Continued on to lga and landed without incident. There is little doubt we may have had a mid-air if it had not been for TCASII. Supplemental information form acn 271057: ATC stated they were unaware of his presence although our TCASII picked up his mode C transponder. Had we descended as instructed to 11000, we may have crossed his flight path and had a possible near miss/incident/accident. Thanks to TCASII we can tell this story!

Original NASA ASRS Text

Title: LGT IN IMC HAS TCASII RA WHEN CLRED FOR AND STARTING DSCNT. RESPONDS WITH CLB.

Narrative: CLRED TO DSND FROM 13000-11000 FT. STARTED DSCNT TO ABOUT 12400 WHEN TCASII CALLED 'TFC.' SHORTLY THEREAFTER (5 SECONDS) TCASII ISSUED RA TO CLB. CLB WAS INITIATED AS TFC WAS SHOWING -- 400 FT ON TCASII. BY THE TIME A POS RATE WAS INDICATED, THE TFC WAS MINUS 200 FT. CAPT LOOKED OUT AND SAW WHAT APPEARED TO BE SMALL BUSINESS JET WITHIN 3-4 MI AND CLOSING RAPIDLY DIRECTLY IN OUR FLT PATH. AS IT PASSED BENEATH US, IT WAS 400-500 FT.BELOW. HE MADE NO EVASIVE MANEUVER AND APPEARED NOT TO SEE US. I INFORMED CTLR WE WERE CLBING AS DIRECTED BY TCASII, HE SAID HE HAD NO TFC IN OUR AREA. LATER HE CALLED BACK AND SAID HE HAD NOT SEEN THE TFC WHICH CAUSED THE CONFLICT. WE CLBED TO 13400 BEFORE AGAIN COMMENCING DSCNT. CONTINUED ON TO LGA AND LANDED WITHOUT INCIDENT. THERE IS LITTLE DOUBT WE MAY HAVE HAD A MID-AIR IF IT HAD NOT BEEN FOR TCASII. SUPPLEMENTAL INFO FORM ACN 271057: ATC STATED THEY WERE UNAWARE OF HIS PRESENCE ALTHOUGH OUR TCASII PICKED UP HIS MODE C XPONDER. HAD WE DSNDED AS INSTRUCTED TO 11000, WE MAY HAVE CROSSED HIS FLT PATH AND HAD A POSSIBLE NEAR MISS/INCIDENT/ACCIDENT. THANKS TO TCASII WE CAN TELL THIS STORY!

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.