Air carrier X TCASII RA from VFR Y unauthorized descent from assigned altitude. Evasive action taken...

Attributes
ACN	250697
Time
Date	199308
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : avp
State Reference	PA
Altitude	msl bound lower : 17000 msl bound upper : 17500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute : direct enroute airway : zny
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	VFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 3
ASRS Report	250697
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time total : 4500
ASRS Report	250629
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 6000 vertical : 500
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	other

Narrative:

Air carrier X was level at 17000 ft VFR traffic was level at 17500 ft. Air carrier X advised he had a TCASII alert and descended to 16000 ft. The aircraft were properly separated. The VFR aircraft Y wasn't descending. Supplemental information from acn 250629: air carrier Y had been leveled off in climb due to VFR traffic at 17500 ft. We received a TA and monitored TCASII (there was 500 ft vertical separation and within approximately 1 mi of traffic). We then received an RA to descend at 1000 FPM to 1500 FPM, which was initiated. We descended approximately 500 ft when we received our 'clear of conflict' from TCASII. We notified ATC during deviation and he couldn't believe we received an RA. He did not point out traffic to us either and we never obtained visual. He said he didn't give us a TA because he felt it would be no factor and didn't think TCASII would given an RA.

Original NASA ASRS Text

Title: ACR X TCASII RA FROM VFR Y UNAUTH DSCNT FROM ASSIGNED ALT. EVASIVE ACTION TAKEN.

Narrative: ACR X WAS LEVEL AT 17000 FT VFR TFC WAS LEVEL AT 17500 FT. ACR X ADVISED HE HAD A TCASII ALERT AND DSNDED TO 16000 FT. THE ACFT WERE PROPERLY SEPARATED. THE VFR ACFT Y WASN'T DSNDING. SUPPLEMENTAL INFORMATION FROM ACN 250629: ACR Y HAD BEEN LEVELED OFF IN CLB DUE TO VFR TFC AT 17500 FT. WE RECEIVED A TA AND MONITORED TCASII (THERE WAS 500 FT VERT SEPARATION AND WITHIN APPROX 1 MI OF TFC). WE THEN RECEIVED AN RA TO DSND AT 1000 FPM TO 1500 FPM, WHICH WAS INITIATED. WE DSNDED APPROX 500 FT WHEN WE RECEIVED OUR 'CLR OF CONFLICT' FROM TCASII. WE NOTIFIED ATC DURING DEV AND HE COULDN'T BELIEVE WE RECEIVED AN RA. HE DID NOT POINT OUT TFC TO US EITHER AND WE NEVER OBTAINED VISUAL. HE SAID HE DIDN'T GIVE US A TA BECAUSE HE FELT IT WOULD BE NO FACTOR AND DIDN'T THINK TCASII WOULD GIVEN AN RA.

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.