Less than legal separation between aircraft departure and arrival at bos.

Attributes
ACN	175129
Time
Date	199104
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : bos
State Reference	MA
Altitude	msl bound lower : 5000 msl bound upper : 9000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : bos
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	cruise other descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : atp pilot : commercial pilot : flight engineer
Experience	flight time last 90 days : 180 flight time total : 10000 flight time type : 800
ASRS Report	175129
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	altitude deviation : overshoot conflict : airborne less severe non adherence : required legal separation non adherence : clearance
Independent Detector	other controllera other flight crewa
Resolutory Action	controller : issued new clearance
Consequence	faa : investigated
Miss Distance	horizontal : 6000 vertical : 1000
Supplementary
Primary Problem	Ambiguous
Air Traffic Incident	Operational Deviation Pilot Deviation other

Narrative:

We were level at 11000' MSL in contact with boston approach. We received clearance to 9000' passing 10000' we were requested to expedite to 9000' and read back the same to the controller. He called out traffic at about 10 O'clock at 7000'. We had no visibility contact. The controller asked our traffic his present altitude and seemed alarmed, traffic was at 9000' in a climb. Hearing this I reported 9000' to the controller and he called the traffic position again and cleared us to 5000'. We began an immediate descent and I inquired if we needed to expedite to 5000', to which he responded affirmative. We then spotted the traffic at 11-12 O'clock at 9000' and climbing. Aside from expediting our descent, no other evasive action was required. The controller may have intended us to initially expedite to 5000' and mistakenly said 9000' or perhaps we heard it wrong and read it back as 9000' and he failed to catch the mistake. The tapes are being checked by boston approach.

Original NASA ASRS Text

Title: LESS THAN LEGAL SEPARATION BETWEEN ACFT DEP AND ARR AT BOS.

Narrative: WE WERE LEVEL AT 11000' MSL IN CONTACT WITH BOSTON APCH. WE RECEIVED CLRNC TO 9000' PASSING 10000' WE WERE REQUESTED TO EXPEDITE TO 9000' AND READ BACK THE SAME TO THE CTLR. HE CALLED OUT TFC AT ABOUT 10 O'CLOCK AT 7000'. WE HAD NO VIS CONTACT. THE CTLR ASKED OUR TFC HIS PRESENT ALT AND SEEMED ALARMED, TFC WAS AT 9000' IN A CLB. HEARING THIS I RPTED 9000' TO THE CTLR AND HE CALLED THE TFC POS AGAIN AND CLRED US TO 5000'. WE BEGAN AN IMMEDIATE DSNT AND I INQUIRED IF WE NEEDED TO EXPEDITE TO 5000', TO WHICH HE RESPONDED AFFIRMATIVE. WE THEN SPOTTED THE TFC AT 11-12 O'CLOCK AT 9000' AND CLBING. ASIDE FROM EXPEDITING OUR DSNT, NO OTHER EVASIVE ACTION WAS REQUIRED. THE CTLR MAY HAVE INTENDED US TO INITIALLY EXPEDITE TO 5000' AND MISTAKENLY SAID 9000' OR PERHAPS WE HEARD IT WRONG AND READ IT BACK AS 9000' AND HE FAILED TO CATCH THE MISTAKE. THE TAPES ARE BEING CHKED BY BOSTON APCH.

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.