Flight crew of a B737 took precautionary evasive action to comply with a TCASII RA for another aircraft crossing through their altitude, according to approach controller advisory.

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Attributes
ACN	483880
Time
Date	200008
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : lga.airport
State Reference	NY
Altitude	msl bound lower : 8300 msl bound upper : 9000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : n90.tracon
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : 4
Flight Phase	descent : approach descent : intermediate altitude
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tracon : n90.tracon
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise : level
Flight Plan	VFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	483880
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : multi engine
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe other anomaly other
Independent Detector	atc equipment other atc equipment : radar aircraft equipment : tcas other flight crewa
Resolutory Action	controller : issued advisory flight crew : took precautionary avoidance action
Miss Distance	horizontal : 12000 vertical : 700
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	other

Narrative:

We were in descent to 9000 ft, when ATC called VFR traffic at 9000 ft and closing at 11 O'clock position. As we were passing 9300 ft for 9000 ft we asked the controller if we should go back up to 9500 ft. He said no. Continue to and maintain 9000 ft. We got a TA for an aircraft at our altitude about 30 seconds later and immediately asked for a lower altitude. When the controller said unable, the first officer told him that we were going to get an RA shortly. We did, with a descend command which resulted in an altitude deviation to 8300 ft and an airspeed deviation of 15 KIAS. We never visually acquired the traffic, but our display had him within 2 mi. We wondered why the controller refused to give us a different altitude than traffic he knew was a direct conflict for us, and why a VFR aircraft was transiting ny airspace at 9000 ft.

Original NASA ASRS Text

Title: FLC OF A B737 TOOK PRECAUTIONARY EVASIVE ACTION TO COMPLY WITH A TCASII RA FOR ANOTHER ACFT XING THROUGH THEIR ALT, ACCORDING TO APCH CTLR ADVISORY.

Narrative: WE WERE IN DSCNT TO 9000 FT, WHEN ATC CALLED VFR TFC AT 9000 FT AND CLOSING AT 11 O'CLOCK POS. AS WE WERE PASSING 9300 FT FOR 9000 FT WE ASKED THE CTLR IF WE SHOULD GO BACK UP TO 9500 FT. HE SAID NO. CONTINUE TO AND MAINTAIN 9000 FT. WE GOT A TA FOR AN ACFT AT OUR ALT ABOUT 30 SECONDS LATER AND IMMEDIATELY ASKED FOR A LOWER ALT. WHEN THE CTLR SAID UNABLE, THE FO TOLD HIM THAT WE WERE GOING TO GET AN RA SHORTLY. WE DID, WITH A DSND COMMAND WHICH RESULTED IN AN ALTDEV TO 8300 FT AND AN AIRSPD DEV OF 15 KIAS. WE NEVER VISUALLY ACQUIRED THE TFC, BUT OUR DISPLAY HAD HIM WITHIN 2 MI. WE WONDERED WHY THE CTLR REFUSED TO GIVE US A DIFFERENT ALT THAN TFC HE KNEW WAS A DIRECT CONFLICT FOR US, AND WHY A VFR ACFT WAS TRANSITING NY AIRSPACE AT 9000 FT.

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.