TCASII RA causes medium large transport to leave assigned altitude.

Attributes
ACN	295727
Time
Date	199502
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : lga
State Reference	NY
Altitude	msl bound lower : 10000 msl bound upper : 11000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : n90
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other descent other
Route In Use	arrival star : star enroute airway : n90
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Flight Phase	cruise other descent other
Flight Plan	VFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : atp pilot : cfi
Experience	flight time last 90 days : 200 flight time total : 6200 flight time type : 2100
ASRS Report	295727
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 12000 vertical : 200
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation other

Narrative:

We were on the milton 6 arrival to lga having originated from ord. We were level at 11000 ft MSL approximately over lizzi intersection. IMC at the time, the TCASII showed traffic at 11500 ft in front of us heading at us. We then received a TCASII alert. I asked the controller about the traffic and he responded it was VFR at 11500 ft MSL. But then the traffic began a descent and TCASII issued an RA to descend. We responded, and I tried to advise the controller that we were descending because of the traffic conflict. After 3 tries for a lower altitude and no response, the captain came on the frequency and very strongly asked the controller if he heard us. The controller finally responded and told us to level off at 10000 ft MSL. (We had asked to either descend or return to 11000 ft MSL). After all was normal and we landed lga we had asked the controller for his phone number and he gave it to us. The captain called and was told that since the traffic was VFR and they weren't talking to him, they didn't need to tell us, plus they said the controller was busy working 6 aircraft. What concerns me, is the controller's lack of response to our urgency and the fact that he didn't even tell us about the traffic. We know he wasn't required to tell us, but 500 ft is too small a margin to not be concerned, especially since the aircraft didn't maintain VFR altitude.

Original NASA ASRS Text

Title: TCASII RA CAUSES MLG TO LEAVE ASSIGNED ALT.

Narrative: WE WERE ON THE MILTON 6 ARR TO LGA HAVING ORIGINATED FROM ORD. WE WERE LEVEL AT 11000 FT MSL APPROX OVER LIZZI INTXN. IMC AT THE TIME, THE TCASII SHOWED TFC AT 11500 FT IN FRONT OF US HDG AT US. WE THEN RECEIVED A TCASII ALERT. I ASKED THE CTLR ABOUT THE TFC AND HE RESPONDED IT WAS VFR AT 11500 FT MSL. BUT THEN THE TFC BEGAN A DSCNT AND TCASII ISSUED AN RA TO DSND. WE RESPONDED, AND I TRIED TO ADVISE THE CTLR THAT WE WERE DSNDING BECAUSE OF THE TFC CONFLICT. AFTER 3 TRIES FOR A LOWER ALT AND NO RESPONSE, THE CAPT CAME ON THE FREQ AND VERY STRONGLY ASKED THE CTLR IF HE HEARD US. THE CTLR FINALLY RESPONDED AND TOLD US TO LEVEL OFF AT 10000 FT MSL. (WE HAD ASKED TO EITHER DSND OR RETURN TO 11000 FT MSL). AFTER ALL WAS NORMAL AND WE LANDED LGA WE HAD ASKED THE CTLR FOR HIS PHONE NUMBER AND HE GAVE IT TO US. THE CAPT CALLED AND WAS TOLD THAT SINCE THE TFC WAS VFR AND THEY WEREN'T TALKING TO HIM, THEY DIDN'T NEED TO TELL US, PLUS THEY SAID THE CTLR WAS BUSY WORKING 6 ACFT. WHAT CONCERNS ME, IS THE CTLR'S LACK OF RESPONSE TO OUR URGENCY AND THE FACT THAT HE DIDN'T EVEN TELL US ABOUT THE TFC. WE KNOW HE WASN'T REQUIRED TO TELL US, BUT 500 FT IS TOO SMALL A MARGIN TO NOT BE CONCERNED, ESPECIALLY SINCE THE ACFT DIDN'T MAINTAIN VFR ALT.

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.