TCASII. VFR aircraft in communication with ATC passed close and under air carrier aircraft.

Attributes
ACN	318280
Time
Date	199510
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : bos
State Reference	MA
Altitude	msl bound lower : 11000 msl bound upper : 11000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zhu
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	descent other
Route In Use	enroute airway : zbw
Flight Plan	IFR
Aircraft 2
Operator	general aviation : corporate
Make Model Name	Gulfstream II
Operating Under FAR Part	Part 91
Navigation In Use	Other Other
Flight Phase	cruise other
Flight Plan	VFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	318280
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
ASRS Report	318279
Events
Anomaly	conflict : airborne less severe other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : returned to intended course or assigned course flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 0 vertical : 400
Supplementary
Air Traffic Incident	other

Narrative:

While descending to 11000 ft, ATC called traffic at 10 O'clock. We called negative contact. ATC advised the traffic had us in sight. As we leveled at 11000 ft the TCASII called traffic and then climb climb, followed quickly by monitor vertical speed and do not descend. A G-2 passed 400 ft underneath us. We called ZBW after landing and were told he was on a VFR flight plan at 10500 ft, so there was legal separation. He still should have avoided passing 400 ft under a descending aircraft that had made it clear he was not in sight.

Original NASA ASRS Text

Title: TCASII. VFR ACFT IN COM WITH ATC PASSED CLOSE AND UNDER ACR ACFT.

Narrative: WHILE DSNDING TO 11000 FT, ATC CALLED TFC AT 10 O'CLOCK. WE CALLED NEGATIVE CONTACT. ATC ADVISED THE TFC HAD US IN SIGHT. AS WE LEVELED AT 11000 FT THE TCASII CALLED TFC AND THEN CLB CLB, FOLLOWED QUICKLY BY MONITOR VERT SPD AND DO NOT DSND. A G-2 PASSED 400 FT UNDERNEATH US. WE CALLED ZBW AFTER LNDG AND WERE TOLD HE WAS ON A VFR FLT PLAN AT 10500 FT, SO THERE WAS LEGAL SEPARATION. HE STILL SHOULD HAVE AVOIDED PASSING 400 FT UNDER A DSNDING ACFT THAT HAD MADE IT CLR HE WAS NOT IN SIGHT.

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.