An air carrier large transport descended in response to a TCASII command.

Attributes
ACN	233698
Time
Date	199302
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : pdz airport : ont
State Reference	CA
Altitude	msl bound lower : 4500 msl bound upper : 5000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	departure other departure sid : sid enroute airway : ont
Flight Plan	IFR
Aircraft 2
Make Model Name	Small Aircraft, High Wing, 1 Eng, Fixed Gear
Flight Phase	cruise other
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 210 flight time total : 8000 flight time type : 3000
ASRS Report	233698
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 225 flight time total : 5500 flight time type : 225
ASRS Report	233699
Events
Anomaly	conflict : nmac other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 0 vertical : 500
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

It was feb/sun/93 afternoon on a nice day. Cleared on the prado departure to 7000 ft. After takeoff, told to level at 5000 ft for traffic. We stopped at 5000 ft. Departure called the traffic at 10 O'clock about 2 mi at 6000 ft. We got him in sight. Then TCASII says 'traffic.' it shows another target at 1-2 O'clock about 2 mi level at our altitude. TCASII then says 'descend' so we do to 4500 ft. Finally acquired the target visually at 1 mi on collision course and ATC, who was very busy a the time, calls out the traffic. This controller's voice was different from the original voice. The instructor had taken over for the trainee. The area over pdz VOR is very crowded. This area needs VFR corridors and a larger arsa. The other aircraft was a high wing small aircraft type heading northeast at 5000 ft, an IFR altitude. Supplemental information from acn 233699: we notified ATC of our descent at which time they began issuing advisories but what was said was unintelligible. Controller was very busy with numerous aircraft, mostly VFR. Our converging traffic apparently was VFR but was not flying at VFR altitude.

Original NASA ASRS Text

Title: AN ACR LGT DSNDED IN RESPONSE TO A TCASII COMMAND.

Narrative: IT WAS FEB/SUN/93 AFTERNOON ON A NICE DAY. CLRED ON THE PRADO DEP TO 7000 FT. AFTER TKOF, TOLD TO LEVEL AT 5000 FT FOR TFC. WE STOPPED AT 5000 FT. DEP CALLED THE TFC AT 10 O'CLOCK ABOUT 2 MI AT 6000 FT. WE GOT HIM IN SIGHT. THEN TCASII SAYS 'TFC.' IT SHOWS ANOTHER TARGET AT 1-2 O'CLOCK ABOUT 2 MI LEVEL AT OUR ALT. TCASII THEN SAYS 'DSND' SO WE DO TO 4500 FT. FINALLY ACQUIRED THE TARGET VISUALLY AT 1 MI ON COLLISION COURSE AND ATC, WHO WAS VERY BUSY A THE TIME, CALLS OUT THE TFC. THIS CTLR'S VOICE WAS DIFFERENT FROM THE ORIGINAL VOICE. THE INSTRUCTOR HAD TAKEN OVER FOR THE TRAINEE. THE AREA OVER PDZ VOR IS VERY CROWDED. THIS AREA NEEDS VFR CORRIDORS AND A LARGER ARSA. THE OTHER ACFT WAS A HIGH WING SMA TYPE HDG NE AT 5000 FT, AN IFR ALT. SUPPLEMENTAL INFO FROM ACN 233699: WE NOTIFIED ATC OF OUR DSCNT AT WHICH TIME THEY BEGAN ISSUING ADVISORIES BUT WHAT WAS SAID WAS UNINTELLIGIBLE. CTLR WAS VERY BUSY WITH NUMEROUS ACFT, MOSTLY VFR. OUR CONVERGING TFC APPARENTLY WAS VFR BUT WAS NOT FLYING AT VFR ALT.

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.