Air carrier flight crew descended to wrong altitude, and received TCASII RA.

Attributes
ACN	309290
Time
Date	199507
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : riv airport : sna
State Reference	CA
Altitude	msl bound lower : 10000 msl bound upper : 12000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ont tower : anc
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	arrival other arrival star : star enroute : direct
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	other : unknown
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 220 flight time total : 6000 flight time type : 1500
ASRS Report	309290
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : commercial pilot : atp pilot : flight engineer
ASRS Report	309410
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : clearance other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance flight crew : took evasive action other
Consequence	Other
Miss Distance	horizontal : 16500 vertical : 0
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

From psp VOR we had been cleared for eastside 1 arrival to sna and to cross bands intersection at 14000 ft. There was quite a bit of congestion on ont approach frequency, and some confusion as to instructions as the approach controller had called us 'other air carrier xxy' by mistake. At approximately XA15L we were cleared direct to kayoh for eastside arrival, but controller told us he'd give us our altitude instructions. Shortly thereafter, ont approach gave us clearance to descend to 10000 ft (at least what we thought was clearance to 10000 ft). As far as I can remember, I read back 10000 ft and set the altitude alert. Passing 12000 ft we noticed a TCASII warning of a TA at our 11 O'clock for 5 mi. The controller told us to descend immediately to 8000 ft, that our clearance was 12000 ft. Simultaneously, the TCASII initiated an evasive descent RA, which we followed. TCASII miss was about 3 mi off our left wing. The remainder of approach was uneventful. Supplemental information from acn 309410: on this day, frequency congestion was heavy.

Original NASA ASRS Text

Title: ACR FLC DSNDED TO WRONG ALT, AND RECEIVED TCASII RA.

Narrative: FROM PSP VOR WE HAD BEEN CLRED FOR EASTSIDE 1 ARR TO SNA AND TO CROSS BANDS INTXN AT 14000 FT. THERE WAS QUITE A BIT OF CONGESTION ON ONT APCH FREQ, AND SOME CONFUSION AS TO INSTRUCTIONS AS THE APCH CTLR HAD CALLED US 'OTHER ACR XXY' BY MISTAKE. AT APPROX XA15L WE WERE CLRED DIRECT TO KAYOH FOR EASTSIDE ARR, BUT CTLR TOLD US HE'D GIVE US OUR ALT INSTRUCTIONS. SHORTLY THEREAFTER, ONT APCH GAVE US CLRNC TO DSND TO 10000 FT (AT LEAST WHAT WE THOUGHT WAS CLRNC TO 10000 FT). AS FAR AS I CAN REMEMBER, I READ BACK 10000 FT AND SET THE ALT ALERT. PASSING 12000 FT WE NOTICED A TCASII WARNING OF A TA AT OUR 11 O'CLOCK FOR 5 MI. THE CTLR TOLD US TO DSND IMMEDIATELY TO 8000 FT, THAT OUR CLRNC WAS 12000 FT. SIMULTANEOUSLY, THE TCASII INITIATED AN EVASIVE DSCNT RA, WHICH WE FOLLOWED. TCASII MISS WAS ABOUT 3 MI OFF OUR L WING. THE REMAINDER OF APCH WAS UNEVENTFUL. SUPPLEMENTAL INFO FROM ACN 309410: ON THIS DAY, FREQ CONGESTION WAS HVY.

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.