Medium large transport has a TCASII RA with an unseen aircraft in the arsa without clearance.

Attributes
ACN	257930
Time
Date	199311
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : orf
State Reference	VA
Altitude	msl bound lower : 2500 msl bound upper : 2500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : orf
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	other
Route In Use	departure : noise abatement
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : flight engineer pilot : commercial pilot : cfi pilot : atp
Experience	flight time last 90 days : 180 flight time total : 8000 flight time type : 3500
ASRS Report	257930
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : commercial pilot : instrument pilot : atp
Experience	flight time last 90 days : 180 flight time total : 15000 flight time type : 11000
ASRS Report	257933
Events
Anomaly	conflict : airborne less severe other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 5000 vertical : 300
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

After being vectored to a left downwind for runway 5 at orf, we were cleared for the visual approach. While turning base leg, over the river (as published in the noise abatement procedure), we observed a TA on our TCASII. The traffic was at our 10 O'clock position, less than 3 mi and level at 2000 ft. As a result, we leveled off at 2500 ft to look for the conflict but we never made visual contact. Immediately thereafter, we received an RA which required a 3000 FPM rate of climb to clear the conflict. We informed the tower of our required action. Appropriately, they told us to continue a go around and vectored us to a right downwind for runway 5, another visual approach, and uneventful landing. In closing, ATC had not warned us of any possible traffic conflicts. Evidently, the traffic did not appear on their radar screen until after our RA advisory. Further, ATC suggested the traffic had entered the arsa without notification and/or clearance. Lastly, we are grateful to TCASII and feel it definitely helped to prevent what could have been a tragic event in orf.

Original NASA ASRS Text

Title: MLG HAS A TCASII RA WITH AN UNSEEN ACFT IN THE ARSA WITHOUT CLRNC.

Narrative: AFTER BEING VECTORED TO A L DOWNWIND FOR RWY 5 AT ORF, WE WERE CLRED FOR THE VISUAL APCH. WHILE TURNING BASE LEG, OVER THE RIVER (AS PUBLISHED IN THE NOISE ABATEMENT PROC), WE OBSERVED A TA ON OUR TCASII. THE TFC WAS AT OUR 10 O'CLOCK POS, LESS THAN 3 MI AND LEVEL AT 2000 FT. AS A RESULT, WE LEVELED OFF AT 2500 FT TO LOOK FOR THE CONFLICT BUT WE NEVER MADE VISUAL CONTACT. IMMEDIATELY THEREAFTER, WE RECEIVED AN RA WHICH REQUIRED A 3000 FPM RATE OF CLB TO CLR THE CONFLICT. WE INFORMED THE TWR OF OUR REQUIRED ACTION. APPROPRIATELY, THEY TOLD US TO CONTINUE A GAR AND VECTORED US TO A R DOWNWIND FOR RWY 5, ANOTHER VISUAL APCH, AND UNEVENTFUL LNDG. IN CLOSING, ATC HAD NOT WARNED US OF ANY POSSIBLE TFC CONFLICTS. EVIDENTLY, THE TFC DID NOT APPEAR ON THEIR RADAR SCREEN UNTIL AFTER OUR RA ADVISORY. FURTHER, ATC SUGGESTED THE TFC HAD ENTERED THE ARSA WITHOUT NOTIFICATION AND/OR CLRNC. LASTLY, WE ARE GRATEFUL TO TCASII AND FEEL IT DEFINITELY HELPED TO PREVENT WHAT COULD HAVE BEEN A TRAGIC EVENT IN ORF.

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.