An MD88 crew has a potential conflict with unknown traffic south of terri intersection with ZDC, dc.

Attributes
ACN	459060
Time
Date	199912
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	intersection : terri
State Reference	PA
Altitude	msl bound lower : 9300 msl bound upper : 10000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdc.artcc
Operator	common carrier : air carrier
Make Model Name	MD-88
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : intermediate altitude
Route In Use	arrival star : dupont 4
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : flight engineer pilot : multi engine
Experience	flight time last 90 days : 210 flight time total : 5000
ASRS Report	459060
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 220 flight time total : 8000 flight time type : 1500
ASRS Report	459065
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne critical non adherence : required legal separation non adherence : published procedure other anomaly other
Independent Detector	aircraft equipment : tcas
Resolutory Action	flight crew : took evasive action
Supplementary
Problem Areas	Aircraft ATC Human Performance Airspace Structure
Primary Problem	Airspace Structure

Narrative:

During dupont 4 arrival into phl, talking with ZDC on frequency 132.05, received TCASII RA. Descended from 10000 ft MSL to 9300 ft MSL. When clear of conflict, climbed back to 10000 ft MSL and resumed arrival.

Original NASA ASRS Text

Title: AN MD88 CREW HAS A POTENTIAL CONFLICT WITH UNKNOWN TFC S OF TERRI INTXN WITH ZDC, DC.

Narrative: DURING DUPONT 4 ARR INTO PHL, TALKING WITH ZDC ON FREQ 132.05, RECEIVED TCASII RA. DSNDED FROM 10000 FT MSL TO 9300 FT MSL. WHEN CLR OF CONFLICT, CLBED BACK TO 10000 FT MSL AND RESUMED ARR.

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.