Near midair collision avoidance by TCASII RA.

Attributes
ACN	206627
Time
Date	199204
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : aml airport : iad
State Reference	VA
Altitude	msl bound lower : 5000 msl bound upper : 5300
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : iad
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Operator	general aviation : personal
Make Model Name	Small Aircraft
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	VFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 150 flight time total : 9200 flight time type : 840
ASRS Report	206627
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : nmac non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 1000 vertical : 300
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

While being vectored to the northwest of iad by dulles approach control, we were cleared to descend to 5000 ft and intercept the aml 300 degree radial inbound. Shortly after level off, TCASII issued a TA alert followed immediately by an RA to climb. The first officer initiated a climb and I advised approach control of our deviation and why. Approach control responded that they just painted traffic at our 12 O'clock 1 1/2 mi at 4700 ft MSL. According to TCASII and approach radar, the conflicting traffic passed underneath our aircraft. We never spotted him visually. We then descended from 6000 ft to 5000 ft and resumed our approach. Execution of SOP following a TCASII RA apparently averted a near midair collision.

Original NASA ASRS Text

Title: NMAC AVOIDANCE BY TCASII RA.

Narrative: WHILE BEING VECTORED TO THE NW OF IAD BY DULLES APCH CTL, WE WERE CLRED TO DSND TO 5000 FT AND INTERCEPT THE AML 300 DEG RADIAL INBOUND. SHORTLY AFTER LEVEL OFF, TCASII ISSUED A TA ALERT FOLLOWED IMMEDIATELY BY AN RA TO CLB. THE FO INITIATED A CLB AND I ADVISED APCH CTL OF OUR DEV AND WHY. APCH CTL RESPONDED THAT THEY JUST PAINTED TFC AT OUR 12 O'CLOCK 1 1/2 MI AT 4700 FT MSL. ACCORDING TO TCASII AND APCH RADAR, THE CONFLICTING TFC PASSED UNDERNEATH OUR ACFT. WE NEVER SPOTTED HIM VISUALLY. WE THEN DSNDED FROM 6000 FT TO 5000 FT AND RESUMED OUR APCH. EXECUTION OF SOP FOLLOWING A TCASII RA APPARENTLY AVERTED A NMAC.

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.