B737-500 flight crew has a TCAS RA during approach to lga.

Attributes
ACN	723300
Time
Date	200701
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : n90.tracon
State Reference	NY
Altitude	msl single value : 4000
Aircraft 1
Controlling Facilities	tracon : n90.tracon
Operator	common carrier : air carrier
Make Model Name	B737-500
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : n90.tracon
Make Model Name	Helicopter
Operating Under FAR Part	Part 91
Flight Phase	climbout : initial
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 120 flight time total : 13000 flight time type : 950
ASRS Report	723300
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Experience	flight time last 90 days : 143 flight time total : 6200 flight time type : 801
ASRS Report	723510
Events
Anomaly	conflict : airborne less severe
Independent Detector	aircraft equipment : tcas other flight crewa other flight crewb
Resolutory Action	flight crew : took precautionary avoidance action
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance Airport
Primary Problem	Ambiguous

Narrative:

We were on arrival to lga at 4000 ft MSL approaching the george washington bridge. ATC had advised another aircraft of VFR traffic over the bridge; so we were looking for the traffic. We noted traffic on our TCAS at 4500 ft near the bridge. We acquired the traffic as we neared the bridge and could identify it as a helicopter. At that time we received an RA to descend. I disconnected the autoplt and autothrottles and initiated the descent. We then advised ATC of our deviation. My first officer noted that as the helicopter passed over the left wing our altitude indicated 3750 ft and the helicopter indicated 4200 ft on the TCAS. We then received a 'clear of conflict' advisory and began to return to our previous clearance. At that time ATC instructed us to descend to 3000 ft. I advised ATC that we would file a report. After landing I called lga approach to discuss the matter. I then advised them that I would file the appropriate report.

Original NASA ASRS Text

Title: B737-500 FLT CREW HAS A TCAS RA DURING APCH TO LGA.

Narrative: WE WERE ON ARR TO LGA AT 4000 FT MSL APCHING THE GEORGE WASHINGTON BRIDGE. ATC HAD ADVISED ANOTHER ACFT OF VFR TFC OVER THE BRIDGE; SO WE WERE LOOKING FOR THE TFC. WE NOTED TFC ON OUR TCAS AT 4500 FT NEAR THE BRIDGE. WE ACQUIRED THE TFC AS WE NEARED THE BRIDGE AND COULD IDENT IT AS A HELI. AT THAT TIME WE RECEIVED AN RA TO DSND. I DISCONNECTED THE AUTOPLT AND AUTOTHROTTLES AND INITIATED THE DSCNT. WE THEN ADVISED ATC OF OUR DEV. MY FO NOTED THAT AS THE HELI PASSED OVER THE L WING OUR ALT INDICATED 3750 FT AND THE HELI INDICATED 4200 FT ON THE TCAS. WE THEN RECEIVED A 'CLR OF CONFLICT' ADVISORY AND BEGAN TO RETURN TO OUR PREVIOUS CLRNC. AT THAT TIME ATC INSTRUCTED US TO DSND TO 3000 FT. I ADVISED ATC THAT WE WOULD FILE A RPT. AFTER LNDG I CALLED LGA APCH TO DISCUSS THE MATTER. I THEN ADVISED THEM THAT I WOULD FILE THE APPROPRIATE RPT.

Data retrieved from NASA's ASRS site as of January 2009 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.