An air carrier MD80 super 80 flight crew reports an near midair collision with an unknown aircraft at 11000 ft near aml. This required the flight crew to execute an evasive action climb twice before they were clear. No apparent comment from the controller, and traffic not sighted.

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Attributes
ACN	425805
Time
Date	199901
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : aml
State Reference	VA
Altitude	msl bound lower : 11000 msl bound upper : 11000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Flight Phase	cruise other cruise other
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Make Model Name	Commercial Fixed Wing
Flight Phase	climbout : intermediate altitude
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
ASRS Report	425805
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial
Events
Anomaly	conflict : nmac other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : took evasive action other
Consequence	Other
Miss Distance	horizontal : 0 vertical : 200

Narrative:

While on the finks 6 arrival to dca, we were vectored from doccs at 15000 ft. We were then cleared to 11000 ft and told to intercept the arrival west of aml. Prior to reaching aml we were instructed to depart aml direct to dca. As we departed aml, TCASII displayed traffic at 10 O'clock below and climbing. The traffic symbol quickly changed to TA then RA with a commanded climb of 2000 FPM. Captain responded immediately. After about 30 seconds, the clear of conflict warning sounded. As the captain started a slow descent towards the assigned altitude, the RA reappeared with a 2000 FPM climb. After about 20 seconds of climb, the clear of conflict sounded again. The flight continued to dca and landed. The crew notified approach each time they deviated due to TCASII. The traffic in conflict passed from 9 O'clock to 3 O'clock with an altitude separation of 200-300 ft. Although the crew was expecting a clearance to cross aml at 8000 ft, it was never received. Radio traffic was very heavy and there was a similar call sign company aircraft on the frequency. WX was IMC.

Original NASA ASRS Text

Title: AN ACR MD80 SUPER 80 FLC RPTS AN NMAC WITH AN UNKNOWN ACFT AT 11000 FT NEAR AML. THIS REQUIRED THE FLC TO EXECUTE AN EVASIVE ACTION CLB TWICE BEFORE THEY WERE CLR. NO APPARENT COMMENT FROM THE CTLR, AND TFC NOT SIGHTED.

Narrative: WHILE ON THE FINKS 6 ARR TO DCA, WE WERE VECTORED FROM DOCCS AT 15000 FT. WE WERE THEN CLRED TO 11000 FT AND TOLD TO INTERCEPT THE ARR W OF AML. PRIOR TO REACHING AML WE WERE INSTRUCTED TO DEPART AML DIRECT TO DCA. AS WE DEPARTED AML, TCASII DISPLAYED TFC AT 10 O'CLOCK BELOW AND CLBING. THE TFC SYMBOL QUICKLY CHANGED TO TA THEN RA WITH A COMMANDED CLB OF 2000 FPM. CAPT RESPONDED IMMEDIATELY. AFTER ABOUT 30 SECONDS, THE CLR OF CONFLICT WARNING SOUNDED. AS THE CAPT STARTED A SLOW DSCNT TOWARDS THE ASSIGNED ALT, THE RA REAPPEARED WITH A 2000 FPM CLB. AFTER ABOUT 20 SECONDS OF CLB, THE CLR OF CONFLICT SOUNDED AGAIN. THE FLT CONTINUED TO DCA AND LANDED. THE CREW NOTIFIED APCH EACH TIME THEY DEVIATED DUE TO TCASII. THE TFC IN CONFLICT PASSED FROM 9 O'CLOCK TO 3 O'CLOCK WITH AN ALT SEPARATION OF 200-300 FT. ALTHOUGH THE CREW WAS EXPECTING A CLRNC TO CROSS AML AT 8000 FT, IT WAS NEVER RECEIVED. RADIO TFC WAS VERY HVY AND THERE WAS A SIMILAR CALL SIGN COMPANY ACFT ON THE FREQ. WX WAS IMC.

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.