Cpr HS1000 deviation altitude after ARTCC controller misses incorrect readback arriving psp.

Attributes
ACN	447952
Time
Date	199909
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : psp.airport
State Reference	CA
Altitude	msl bound lower : 20300 msl bound upper : 21000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zla.artcc
Operator	general aviation : corporate
Make Model Name	BAe 125 Series 1000
Operating Under FAR Part	Part 91
Flight Phase	descent : intermediate altitude descent : vacating altitude
Route In Use	arrival : on vectors
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zla.artcc
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : level
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 210 flight time total : 6543 flight time type : 900
ASRS Report	447952
Person 2
Affiliation	company : corporate
Function	flight crew : first officer
Qualification	pilot : commercial pilot : multi engine pilot : instrument
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne critical non adherence : clearance non adherence : far
Independent Detector	other controllera other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance controller : issued alert flight crew : exited adverse environment flight crew : returned to assigned altitude
Consequence	faa : reviewed incident with flight crew faa : investigated other
Supplementary
Problem Areas	Environmental Factor Airspace Structure Flight Crew Human Performance ATC Human Performance
Primary Problem	Ambiguous
Air Traffic Incident	Pilot Deviation

Narrative:

I was en route from smf to psp. I was PIC of aircraft. I was in right seat. A junior captain was flying in the left seat. We were in a slow descent from FL330. ATC was very busy. We were given dscnts in 1000 ft increments in a very rhythmic fashion just prior to leveling at the prescribed altitude. Prior to leveling at FL210. ATC gave us what we later found out was a traffic report. 'Traffic 10-11 O'clock, 2 mi, FL200.' we thought ATC told us to descend and maintain FL200. We provided the standard readback, 'roger, descend and maintain FL200.' ATC did not catch our mistake, nor did we. We proceeded past FL210 to FL200. After a few seconds of quiet, ATC asked us to verify our altitude of FL210. I replied, 'was cleared to FL200, but we will return to FL210.' he replied (ATC), 'maintain FL210, traffic 10-11 O'clock, B737, 2 mi.' we were back at FL210 by then and replied, 'no joy, level FL210.' bottom of altitude deviation was FL203. Autoplt was on the whole time except for altitude correction. As soon as we replied level FL210, ATC cleared us to 'descend and maintain FL200.' once on the ground, psp ATC asked us to call ZLA. ZLA operational supervisor spoke to me. Informed me of the details of the tape. Aircraft in loss of separation was lost. After reviewing tapes, it was clear we mistook the traffic report for another 1000 ft descent and the controller did not catch the faulty readback from me. The controller was immediately taken off duty for 'retraining.' my first officer and I were also taken off flight status and brought back to headquarters for debriefing and possible/certain retraining. I feel both parties are very proactive in remedying this situation.

Original NASA ASRS Text

Title: CPR HS1000 DEV ALT AFTER ARTCC CTLR MISSES INCORRECT READBACK ARRIVING PSP.

Narrative: I WAS ENRTE FROM SMF TO PSP. I WAS PIC OF ACFT. I WAS IN R SEAT. A JUNIOR CAPT WAS FLYING IN THE L SEAT. WE WERE IN A SLOW DSCNT FROM FL330. ATC WAS VERY BUSY. WE WERE GIVEN DSCNTS IN 1000 FT INCREMENTS IN A VERY RHYTHMIC FASHION JUST PRIOR TO LEVELING AT THE PRESCRIBED ALT. PRIOR TO LEVELING AT FL210. ATC GAVE US WHAT WE LATER FOUND OUT WAS A TFC RPT. 'TFC 10-11 O'CLOCK, 2 MI, FL200.' WE THOUGHT ATC TOLD US TO DSND AND MAINTAIN FL200. WE PROVIDED THE STANDARD READBACK, 'ROGER, DSND AND MAINTAIN FL200.' ATC DID NOT CATCH OUR MISTAKE, NOR DID WE. WE PROCEEDED PAST FL210 TO FL200. AFTER A FEW SECONDS OF QUIET, ATC ASKED US TO VERIFY OUR ALT OF FL210. I REPLIED, 'WAS CLRED TO FL200, BUT WE WILL RETURN TO FL210.' HE REPLIED (ATC), 'MAINTAIN FL210, TFC 10-11 O'CLOCK, B737, 2 MI.' WE WERE BACK AT FL210 BY THEN AND REPLIED, 'NO JOY, LEVEL FL210.' BOTTOM OF ALTDEV WAS FL203. AUTOPLT WAS ON THE WHOLE TIME EXCEPT FOR ALT CORRECTION. AS SOON AS WE REPLIED LEVEL FL210, ATC CLRED US TO 'DSND AND MAINTAIN FL200.' ONCE ON THE GND, PSP ATC ASKED US TO CALL ZLA. ZLA OPERATIONAL SUPVR SPOKE TO ME. INFORMED ME OF THE DETAILS OF THE TAPE. ACFT IN LOSS OF SEPARATION WAS LOST. AFTER REVIEWING TAPES, IT WAS CLR WE MISTOOK THE TFC RPT FOR ANOTHER 1000 FT DSCNT AND THE CTLR DID NOT CATCH THE FAULTY READBACK FROM ME. THE CTLR WAS IMMEDIATELY TAKEN OFF DUTY FOR 'RETRAINING.' MY FO AND I WERE ALSO TAKEN OFF FLT STATUS AND BROUGHT BACK TO HEADQUARTERS FOR DEBRIEFING AND POSSIBLE/CERTAIN RETRAINING. I FEEL BOTH PARTIES ARE VERY PROACTIVE IN REMEDYING THIS SIT.

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.