Medium large transport on arrival, has TCASII RA to descend.

Attributes
ACN	235505
Time
Date	199303
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : sli
State Reference	CA
Altitude	msl bound lower : 15500 msl bound upper : 16000
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : zla
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	arrival other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : commercial pilot : flight engineer pilot : instrument
Experience	flight time last 90 days : 125 flight time total : 15000 flight time type : 4500
ASRS Report	235505
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 12000
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	other

Narrative:

Flying standard arrival to lax and assigned 16000 ft by ZLA (level at 16000 ft). Center advised 2 targets (both IFR or in contact with center). Aircraft #1 climbing through our altitude and passing off of our left side, aircraft #2 ahead of us and climbing to level below our assigned altitude (climbing to 15000 ft, I believe). #1 traffic call was picked up visually by captain (PNF) and indicated on TCASII (visual acquisition difficult due sun angle). Separation (visually) was substantial with no requirement for action. However, TCASII went into RA and commanded approximately 2000 FPM descent. ATC was advised that we were descending due to TCASII. At approximately 15500 ft TCASII RA ceased and original assigned altitude was resumed (16000 ft). Shortly after returning to 16000 ft the captain (PNF) visually acquired the previously reported air carrier (#2 target) passing several thousand ft below (no TCASII display). ATC responded to the call of initial descent from 16000 ft (assigned) but appeared to be somewhat confused (normal) with this unexpected action. ATC later indicated that we had descended into 'reserved' airspace (probably reserved for separation between us and the oncoming jet). General: no 'near miss' condition appeared to exist, however, the #1 target aircraft did get close enough to cause RA on TCASII. The most serious potential for collision appeared to be from descending into an oncoming climbing aircraft (distance between planes precluded this occurrence). Visually (VMC) this RA was somewhat 'inconvenient.' in IMC it would have been 'damn uncomfortable.'

Original NASA ASRS Text

Title: MLG ON ARR, HAS TCASII RA TO DSND.

Narrative: FLYING STANDARD ARR TO LAX AND ASSIGNED 16000 FT BY ZLA (LEVEL AT 16000 FT). CTR ADVISED 2 TARGETS (BOTH IFR OR IN CONTACT WITH CTR). ACFT #1 CLBING THROUGH OUR ALT AND PASSING OFF OF OUR L SIDE, ACFT #2 AHEAD OF US AND CLBING TO LEVEL BELOW OUR ASSIGNED ALT (CLBING TO 15000 FT, I BELIEVE). #1 TFC CALL WAS PICKED UP VISUALLY BY CAPT (PNF) AND INDICATED ON TCASII (VISUAL ACQUISITION DIFFICULT DUE SUN ANGLE). SEPARATION (VISUALLY) WAS SUBSTANTIAL WITH NO REQUIREMENT FOR ACTION. HOWEVER, TCASII WENT INTO RA AND COMMANDED APPROX 2000 FPM DSCNT. ATC WAS ADVISED THAT WE WERE DSNDING DUE TO TCASII. AT APPROX 15500 FT TCASII RA CEASED AND ORIGINAL ASSIGNED ALT WAS RESUMED (16000 FT). SHORTLY AFTER RETURNING TO 16000 FT THE CAPT (PNF) VISUALLY ACQUIRED THE PREVIOUSLY RPTED ACR (#2 TARGET) PASSING SEVERAL THOUSAND FT BELOW (NO TCASII DISPLAY). ATC RESPONDED TO THE CALL OF INITIAL DSCNT FROM 16000 FT (ASSIGNED) BUT APPEARED TO BE SOMEWHAT CONFUSED (NORMAL) WITH THIS UNEXPECTED ACTION. ATC LATER INDICATED THAT WE HAD DSNDED INTO 'RESERVED' AIRSPACE (PROBABLY RESERVED FOR SEPARATION BTWN US AND THE ONCOMING JET). GENERAL: NO 'NEAR MISS' CONDITION APPEARED TO EXIST, HOWEVER, THE #1 TARGET ACFT DID GET CLOSE ENOUGH TO CAUSE RA ON TCASII. THE MOST SERIOUS POTENTIAL FOR COLLISION APPEARED TO BE FROM DSNDING INTO AN ONCOMING CLBING ACFT (DISTANCE BTWN PLANES PRECLUDED THIS OCCURRENCE). VISUALLY (VMC) THIS RA WAS SOMEWHAT 'INCONVENIENT.' IN IMC IT WOULD HAVE BEEN 'DAMN UNCOMFORTABLE.'

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.