An air carrier B777 received and responded to a TCASII RA to descend and saw a VFR BE20 pass 200 ft directly overhead. The BE20 apparently never saw the B777 and controller credits the TCASII for a save.

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Attributes
ACN	350936
Time
Date	199610
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : aml airport : iad
State Reference	VA
Altitude	msl bound lower : 3300 msl bound upper : 3500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : iad
Operator	common carrier : air carrier
Make Model Name	B777 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent : approach
Route In Use	arrival other
Flight Plan	IFR
Aircraft 2
Operator	general aviation : personal
Make Model Name	Super King Air 200/Huron
Operating Under FAR Part	Part 91
Flight Phase	cruise other
Route In Use	enroute : on vectors
Flight Plan	VFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller military : 10 controller radar : 10
ASRS Report	350936
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	conflict : nmac
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 0 vertical : 200
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

B777 on final runway 12 gets RA to descend. VFR BE20 on vector northeast passed 200 ft (pilot report) over B777. B777 was at 3500 ft when he notified tower of RA. The beechcraft was VFR and northbound and did not see the boeing even though he was 200 ft above the boeing and in VFR conditions. Thank god for TCASII!

Original NASA ASRS Text

Title: AN ACR B777 RECEIVED AND RESPONDED TO A TCASII RA TO DSND AND SAW A VFR BE20 PASS 200 FT DIRECTLY OVERHEAD. THE BE20 APPARENTLY NEVER SAW THE B777 AND CTLR CREDITS THE TCASII FOR A SAVE.

Narrative: B777 ON FINAL RWY 12 GETS RA TO DSND. VFR BE20 ON VECTOR NE PASSED 200 FT (PLT RPT) OVER B777. B777 WAS AT 3500 FT WHEN HE NOTIFIED TWR OF RA. THE BEECHCRAFT WAS VFR AND NBOUND AND DID NOT SEE THE BOEING EVEN THOUGH HE WAS 200 FT ABOVE THE BOEING AND IN VFR CONDITIONS. THANK GOD FOR TCASII!

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.