Reporter questions response needed on a TCASII TA on non mode C aircraft.

Attributes
ACN	181999
Time
Date	199106
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : lax
State Reference	CA
Altitude	msl bound lower : 5000 msl bound upper : 5000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : lax
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	arrival other arrival star : star
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : flight engineer pilot : cfi pilot : atp
Experience	flight time last 90 days : 200 flight time total : 9100 flight time type : 650
ASRS Report	181999
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	none taken : anomaly accepted
Consequence	Other
Supplementary
Air Traffic Incident	other

Narrative:

I am flying aircraft that are now more frequently TCAS-equipped. It's a good system, however I am seeing a lot of TA's on non mode C equipped intruders. West/O altitude information, TCAS cannot separate us, and it is difficult for us to find the traffic visually. In the above case on approach to lax, because of the shape of the TCA in that area and the prevailing WX conditions, and the fact that we could not see any traffic at 12 O'clock and closing, we assumed that the intruder was low, below the overcast. We never found out where he was, and ATC was too busy to call out traffic to allow us to ask about it. It puts us in a real quandary when we get a TA with no altitude, 12 O'clock, closing. If we can't see him--we almost never can--do we try to turn to avoid him? Is the TCAS bearing accurate enough for that kind of maneuver? Which way do we turn? Until either all aircraft above, below or in our airspace have mode C or until we all get TCAS 3 (which will give horizontal RA's), we're going to be guessing and hoping. Our airline's procedures and training do not adequately cover this situation.

Original NASA ASRS Text

Title: REPORTER QUESTIONS RESPONSE NEEDED ON A TCASII TA ON NON MODE C ACFT.

Narrative: I AM FLYING ACFT THAT ARE NOW MORE FREQUENTLY TCAS-EQUIPPED. IT'S A GOOD SYS, HOWEVER I AM SEEING A LOT OF TA'S ON NON MODE C EQUIPPED INTRUDERS. W/O ALT INFO, TCAS CANNOT SEPARATE US, AND IT IS DIFFICULT FOR US TO FIND THE TFC VISUALLY. IN THE ABOVE CASE ON APCH TO LAX, BECAUSE OF THE SHAPE OF THE TCA IN THAT AREA AND THE PREVAILING WX CONDITIONS, AND THE FACT THAT WE COULD NOT SEE ANY TFC AT 12 O'CLOCK AND CLOSING, WE ASSUMED THAT THE INTRUDER WAS LOW, BELOW THE OVCST. WE NEVER FOUND OUT WHERE HE WAS, AND ATC WAS TOO BUSY TO CALL OUT TFC TO ALLOW US TO ASK ABOUT IT. IT PUTS US IN A REAL QUANDARY WHEN WE GET A TA WITH NO ALT, 12 O'CLOCK, CLOSING. IF WE CAN'T SEE HIM--WE ALMOST NEVER CAN--DO WE TRY TO TURN TO AVOID HIM? IS THE TCAS BEARING ACCURATE ENOUGH FOR THAT KIND OF MANEUVER? WHICH WAY DO WE TURN? UNTIL EITHER ALL ACFT ABOVE, BELOW OR IN OUR AIRSPACE HAVE MODE C OR UNTIL WE ALL GET TCAS 3 (WHICH WILL GIVE HORIZ RA'S), WE'RE GOING TO BE GUESSING AND HOPING. OUR AIRLINE'S PROCS AND TRNING DO NOT ADEQUATELY COVER THIS SITUATION.

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.