Reporter experiences TCASII RA from intruder conducting visual through 300 ft thick IMC cloud layer.

Attributes
ACN	308948
Time
Date	199506
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : lax
State Reference	CA
Altitude	agl bound lower : 1500 agl bound upper : 1500
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tower : lax
Operator	common carrier : air carrier
Make Model Name	B757 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent : approach
Route In Use	approach : straight in
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 135
Flight Phase	descent : approach
Route In Use	approach : visual
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 200 flight time total : 14000 flight time type : 2000
ASRS Report	308948
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	conflict : airborne less severe other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	none taken : anomaly accepted
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

On ILS approach to runway 25L at lax, we experienced an alarming TCASII RA. Prior to the final approach fix, approach control advised us of commuter traffic for runway 25R who was intercepting runway 25R final from the south. We were told he had us in sight. At about 1500 ft AGL our TCASII which was set at 5 NM range and 'normal' gave us a TA which was close (less than a mi) at our 5 O'clock position, plus 300 ft. We entered the clouds at about 1300 ft AGL and we received another TA. He was closing. Descending below the cloud layer, at about 1200 ft AGL the TCASII TA shifted to a RA which had merged with the center of our TCASII screen, the altitude indicator was shifting from plus to minus while the aural alert called for an immediate climb in excess of 1500 FPM. We advised tower we were executing a TCASII RA and lax tower informed us that our traffic which we never saw had us in sight. We continued our approach to an uneventful landing. This is formation flying (including running rendezvous) in marginal WX. 1 aircraft IFR, the other VFR. It scares the passenger and it scares me, too. It's unacceptable.

Original NASA ASRS Text

Title: RPTR EXPERIENCES TCASII RA FROM INTRUDER CONDUCTING VISUAL THROUGH 300 FT THICK IMC CLOUD LAYER.

Narrative: ON ILS APCH TO RWY 25L AT LAX, WE EXPERIENCED AN ALARMING TCASII RA. PRIOR TO THE FINAL APCH FIX, APCH CTL ADVISED US OF COMMUTER TFC FOR RWY 25R WHO WAS INTERCEPTING RWY 25R FINAL FROM THE S. WE WERE TOLD HE HAD US IN SIGHT. AT ABOUT 1500 FT AGL OUR TCASII WHICH WAS SET AT 5 NM RANGE AND 'NORMAL' GAVE US A TA WHICH WAS CLOSE (LESS THAN A MI) AT OUR 5 O'CLOCK POS, PLUS 300 FT. WE ENTERED THE CLOUDS AT ABOUT 1300 FT AGL AND WE RECEIVED ANOTHER TA. HE WAS CLOSING. DSNDING BELOW THE CLOUD LAYER, AT ABOUT 1200 FT AGL THE TCASII TA SHIFTED TO A RA WHICH HAD MERGED WITH THE CTR OF OUR TCASII SCREEN, THE ALT INDICATOR WAS SHIFTING FROM PLUS TO MINUS WHILE THE AURAL ALERT CALLED FOR AN IMMEDIATE CLB IN EXCESS OF 1500 FPM. WE ADVISED TWR WE WERE EXECUTING A TCASII RA AND LAX TWR INFORMED US THAT OUR TFC WHICH WE NEVER SAW HAD US IN SIGHT. WE CONTINUED OUR APCH TO AN UNEVENTFUL LNDG. THIS IS FORMATION FLYING (INCLUDING RUNNING RENDEZVOUS) IN MARGINAL WX. 1 ACFT IFR, THE OTHER VFR. IT SCARES THE PAX AND IT SCARES ME, TOO. IT'S UNACCEPTABLE.

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.