Air carrier X improper use of TCASII made turn and altitude deviation of 500 ft.

Attributes
ACN	272528
Time
Date	199405
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : aml
State Reference	VA
Altitude	msl bound lower : 6200 msl bound upper : 7500
Environment
Flight Conditions	IMC
Light	Dusk
Aircraft 1
Controlling Facilities	tracon : iad
Operator	common carrier : air carrier
Make Model Name	A320
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	climbout : intermediate altitude descent other
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 180 flight time total : 9000 flight time type : 2500
ASRS Report	272528
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : clearance other spatial deviation
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance flight crew : took evasive action other
Consequence	Other
Miss Distance	horizontal : 12000 vertical : 100
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

WX near aml VOR on bucko 3 arrival into dca precluded air carrier X, a normal arrival over aml. X had deviated to the north around several WX cells and was approximately 15-20 mi north of aml when we received clearance from 8000 ft to 6000 ft. As we descended through 6700 ft, we were advised of Y (a light aircraft, I believe) at 11 O'clock and 5 mi at 6200 ft. X descended to 6300-6200 ft before climbing back to 7000 ft as requested. We were in IMC conditions and both captain and first officer on 40 mi scale on the navigation displays. It appeared as if the TCASII was indicating a near merge plot. An evasive turn to the southwest and rapid climb initiated. X re-leveled at approximately 7500 ft. No TCASII TA or RA generated. No ATC traffic conflict warning generated. We think we were within 3 mi and close to same altitude as opposing Y.

Original NASA ASRS Text

Title: ACR X IMPROPER USE OF TCASII MADE TURN AND ALTDEV OF 500 FT.

Narrative: WX NEAR AML VOR ON BUCKO 3 ARR INTO DCA PRECLUDED ACR X, A NORMAL ARR OVER AML. X HAD DEVIATED TO THE N AROUND SEVERAL WX CELLS AND WAS APPROX 15-20 MI N OF AML WHEN WE RECEIVED CLRNC FROM 8000 FT TO 6000 FT. AS WE DSNDED THROUGH 6700 FT, WE WERE ADVISED OF Y (A LIGHT ACFT, I BELIEVE) AT 11 O'CLOCK AND 5 MI AT 6200 FT. X DSNDED TO 6300-6200 FT BEFORE CLBING BACK TO 7000 FT AS REQUESTED. WE WERE IN IMC CONDITIONS AND BOTH CAPT AND FO ON 40 MI SCALE ON THE NAV DISPLAYS. IT APPEARED AS IF THE TCASII WAS INDICATING A NEAR MERGE PLOT. AN EVASIVE TURN TO THE SW AND RAPID CLB INITIATED. X RE-LEVELED AT APPROX 7500 FT. NO TCASII TA OR RA GENERATED. NO ATC TFC CONFLICT WARNING GENERATED. WE THINK WE WERE WITHIN 3 MI AND CLOSE TO SAME ALT AS OPPOSING Y.

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.