A B757 flight crew experienced a TCASII RA while descending.

Attributes
ACN	520560
Time
Date	200108
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : zma.artcc
State Reference	FL
Altitude	msl single value : 18000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : mia.tower
Operator	common carrier : air carrier
Make Model Name	B757-200
Flight Phase	descent : intermediate altitude
Route In Use	arrival star : surfn 7
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : private pilot : multi engine pilot : flight engineer pilot : commercial pilot : atp pilot : instrument
Experience	flight time last 90 days : 200 flight time total : 7000 flight time type : 2200
ASRS Report	520560
Events
Anomaly	conflict : airborne critical other anomaly other
Resolutory Action	controller : issued advisory flight crew : took evasive action flight crew : took precautionary avoidance action
Supplementary
Problem Areas	Flight Crew Human Performance Airspace Structure ATC Human Performance
Primary Problem	ATC Human Performance

Narrative:

Was flying the surfn 7 STAR into pbi. Was between orm and surfn, executing an FMS VNAV descent (on autoplt) to cross swomp at 8000 ft, as published. Was rapidly approaching FL180 (at 2500+ FPM descent) when ATC advised that an unidented target just popped up on his radar at 17400 ft MSL and looked like it was going to be a conflict. He suggested I level at FL180 until the target could be verified clear. I immediately hit altitude hold since we were rapidly approaching FL180. This was accompanied by a TCASII TA. The traffic was not in sight. Due to the high rate of descent, the autoplt dipped slightly below FL180 as it captured the altitude. During the dip below FL180, we got a TCASII RA climb advisory, which we executed as directed. ATC assisted us in monitoring the other aircraft. ATC advised that the other aircraft was not in radio contact and took no evasive action (no heading or altitude changes), leading us both to believe the other aircraft was unaware of the incident. ATC did a great job with the advance warning and likely prevented a more serious accident/incident from occurring. There wasn't much time to react and there would have been even less time without the ATC advisory.

Original NASA ASRS Text

Title: A B757 FLT CREW EXPERIENCED A TCASII RA WHILE DSNDING.

Narrative: WAS FLYING THE SURFN 7 STAR INTO PBI. WAS BTWN ORM AND SURFN, EXECUTING AN FMS VNAV DSCNT (ON AUTOPLT) TO CROSS SWOMP AT 8000 FT, AS PUBLISHED. WAS RAPIDLY APCHING FL180 (AT 2500+ FPM DSCNT) WHEN ATC ADVISED THAT AN UNIDENTED TARGET JUST POPPED UP ON HIS RADAR AT 17400 FT MSL AND LOOKED LIKE IT WAS GOING TO BE A CONFLICT. HE SUGGESTED I LEVEL AT FL180 UNTIL THE TARGET COULD BE VERIFIED CLR. I IMMEDIATELY HIT ALT HOLD SINCE WE WERE RAPIDLY APCHING FL180. THIS WAS ACCOMPANIED BY A TCASII TA. THE TFC WAS NOT IN SIGHT. DUE TO THE HIGH RATE OF DSCNT, THE AUTOPLT DIPPED SLIGHTLY BELOW FL180 AS IT CAPTURED THE ALT. DURING THE DIP BELOW FL180, WE GOT A TCASII RA CLB ADVISORY, WHICH WE EXECUTED AS DIRECTED. ATC ASSISTED US IN MONITORING THE OTHER ACFT. ATC ADVISED THAT THE OTHER ACFT WAS NOT IN RADIO CONTACT AND TOOK NO EVASIVE ACTION (NO HDG OR ALT CHANGES), LEADING US BOTH TO BELIEVE THE OTHER ACFT WAS UNAWARE OF THE INCIDENT. ATC DID A GREAT JOB WITH THE ADVANCE WARNING AND LIKELY PREVENTED A MORE SERIOUS ACCIDENT/INCIDENT FROM OCCURRING. THERE WASN'T MUCH TIME TO REACT AND THERE WOULD HAVE BEEN EVEN LESS TIME WITHOUT THE ATC ADVISORY.

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.