Air carrier X did not receive TCASII TA on small aircraft.

Attributes
ACN	237680
Time
Date	199303
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : dfw
State Reference	TX
Altitude	msl bound lower : 2500 msl bound upper : 3000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : dfw tower : hou
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent : approach
Flight Plan	IFR
Aircraft 2
Operator	general aviation : personal
Make Model Name	Small Aircraft, High Wing, 1 Eng, Fixed Gear
Flight Phase	cruise other
Flight Plan	VFR
Person 1
Affiliation	government : faa
Function	observation : observer
Qualification	controller : radar
Experience	controller radar : 7
ASRS Report	237680
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	conflict : airborne less severe
Independent Detector	other controllera
Resolutory Action	other
Consequence	Other
Miss Distance	horizontal : 9000 vertical : 500
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Dfw approach issued traffic '1 O'clock 3 mi eastbound, an small aircraft at 2500.' the TCASII showed no traffic. The small aircraft was sighted as it passed 12 O'clock with air carrier X at about 3000. TCASII did not identify the small aircraft until it had passed to 11 O'clock, I think, because of the location of the transponder antenna on the small aircraft. The wing apparently blocked the signal until the small aircraft got to our 11 O'clock. The point: pilots must be aware that TCASII does not 'see' everything.

Original NASA ASRS Text

Title: ACR X DID NOT RECEIVE TCASII TA ON SMA.

Narrative: DFW APCH ISSUED TFC '1 O'CLOCK 3 MI EBOUND, AN SMA AT 2500.' THE TCASII SHOWED NO TFC. THE SMA WAS SIGHTED AS IT PASSED 12 O'CLOCK WITH ACR X AT ABOUT 3000. TCASII DID NOT IDENT THE SMA UNTIL IT HAD PASSED TO 11 O'CLOCK, I THINK, BECAUSE OF THE LOCATION OF THE XPONDER ANTENNA ON THE SMA. THE WING APPARENTLY BLOCKED THE SIGNAL UNTIL THE SMA GOT TO OUR 11 O'CLOCK. THE POINT: PLTS MUST BE AWARE THAT TCASII DOES NOT 'SEE' EVERYTHING.

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.