An air carrier flight crew received a TCASII RA while operating near the floor of class B airspace i...

Attributes
ACN	303016
Time
Date	199504
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : bos
State Reference	MA
Altitude	msl bound lower : 2500 msl bound upper : 3000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : bos tower : cmi
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	other : unknown
Flight Phase	climbout : initial climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial pilot : cfi pilot : flight engineer
Experience	flight time last 90 days : 250 flight time total : 4700 flight time type : 3200
ASRS Report	303016
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 other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera other flight crewa
Resolutory Action	controller : issued new clearance flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 9000 vertical : 300
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	other

Narrative:

On base leg to ILS runway 4R boston. Heading 310 degrees at 3000 ft told to intercept localizer. Traffic called at 2700 ft 10 O'clock idented traffic on TCASII. TCASII alerted 'traffic, traffic,' then announced, 'descend crossing descend.' captain flying followed vsi command to approximately 1200 FPM down. First officer (me) called ATC and informed we followed TCASII and leveled at 2500 ft after TCASII announced, 'clear of conflict,' closest distance from target was approximately 1 1/2 - 2 mi. Called ATC and said we were going back to 3000 ft. He then said to maintain 2500 ft and cleared for the approach. (He seemed irritated a little but made no further comment). We never acquired traffic visually. Continued approach and landing without incident. On ground, ground controller requested us to call TRACON. Controller was curious why we had descended and not climbed. Captain, said we were following our RA as per our company policy. The aircraft apparently was departing norwood airport and was only 300 ft below floor of class B on approach corridor for runway 4R. Under IMC departures from norwood should be restr to lower altitudes. Possibly other aircraft was climbing into our altitude precipitating the RA. Overall, good job by flight crew and cockpit resource management was excellent.

Original NASA ASRS Text

Title: AN ACR FLC RECEIVED A TCASII RA WHILE OPERATING NEAR THE FLOOR OF CLASS B AIRSPACE IN IMC.

Narrative: ON BASE LEG TO ILS RWY 4R BOSTON. HDG 310 DEGS AT 3000 FT TOLD TO INTERCEPT LOC. TFC CALLED AT 2700 FT 10 O'CLOCK IDENTED TFC ON TCASII. TCASII ALERTED 'TFC, TFC,' THEN ANNOUNCED, 'DSND XING DSND.' CAPT FLYING FOLLOWED VSI COMMAND TO APPROX 1200 FPM DOWN. FO (ME) CALLED ATC AND INFORMED WE FOLLOWED TCASII AND LEVELED AT 2500 FT AFTER TCASII ANNOUNCED, 'CLR OF CONFLICT,' CLOSEST DISTANCE FROM TARGET WAS APPROX 1 1/2 - 2 MI. CALLED ATC AND SAID WE WERE GOING BACK TO 3000 FT. HE THEN SAID TO MAINTAIN 2500 FT AND CLRED FOR THE APCH. (HE SEEMED IRRITATED A LITTLE BUT MADE NO FURTHER COMMENT). WE NEVER ACQUIRED TFC VISUALLY. CONTINUED APCH AND LNDG WITHOUT INCIDENT. ON GND, GND CTLR REQUESTED US TO CALL TRACON. CTLR WAS CURIOUS WHY WE HAD DSNDED AND NOT CLBED. CAPT, SAID WE WERE FOLLOWING OUR RA AS PER OUR COMPANY POLICY. THE ACFT APPARENTLY WAS DEPARTING NORWOOD ARPT AND WAS ONLY 300 FT BELOW FLOOR OF CLASS B ON APCH CORRIDOR FOR RWY 4R. UNDER IMC DEPS FROM NORWOOD SHOULD BE RESTR TO LOWER ALTS. POSSIBLY OTHER ACFT WAS CLBING INTO OUR ALT PRECIPITATING THE RA. OVERALL, GOOD JOB BY FLC AND COCKPIT RESOURCE MGMNT WAS EXCELLENT.

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.

An air carrier flight crew received a TCASII RA while operating near the floor of class B airspace in IMC.