B737-300 flight crew descend to incorrect altitude when assigned the sunset STAR due to incorrect L30 phraseology interpretation.

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Attributes
ACN	605674
Time
Date	200401
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	intersection : tragr
State Reference	NV
Altitude	msl bound lower : 12000 msl bound upper : 13000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : l30.tracon
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : approach
Route In Use	arrival star : sunset 1
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 120 flight time total : 28000 flight time type : 14000
ASRS Report	605674
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	altitude deviation : overshoot altitude deviation : crossing restriction not met non adherence : published procedure non adherence : clearance
Independent Detector	atc equipment other atc equipment : radar other controllera
Resolutory Action	controller : issued advisory controller : issued new clearance
Consequence	faa : assigned or threatened penalties faa : investigated faa : reviewed incident with flight crew
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

During the sunset 1 arrival to las, we were cleared to descend via the sunset 1. Approaching tragr intersection (at 16000 ft), we were reclred to 'descend via the sunset 1, except now descend to and maintain 13000 ft.' both my first officer and I interpreted this to mean descend now to 13000 ft and upon reaching continue descent via the sunset 1. At 12000 ft, we were advised by approach control we should be at 13000 ft and to call the TRACON for a possible deviation. I talked to the TRACON supervisor who said she had listened to the tape and would be sending the matter to the regional coordinator to decide how it should be handled. She also said there was no traffic conflict. I believe this could have been prevented by training the controllers not to issue ambiguous or conflicting descent clrncs. If the controller only wanted me to descend to 13000 ft, he should not have prefaced it with descend via the sunset 1. Also, pilots should not accept clrncs until they clearly understand the controller's intent.

Original NASA ASRS Text

Title: B737-300 FLT CREW DSND TO INCORRECT ALT WHEN ASSIGNED THE SUNSET STAR DUE TO INCORRECT L30 PHRASEOLOGY INTERP.

Narrative: DURING THE SUNSET 1 ARR TO LAS, WE WERE CLRED TO DSND VIA THE SUNSET 1. APCHING TRAGR INTXN (AT 16000 FT), WE WERE RECLRED TO 'DSND VIA THE SUNSET 1, EXCEPT NOW DSND TO AND MAINTAIN 13000 FT.' BOTH MY FO AND I INTERPED THIS TO MEAN DSND NOW TO 13000 FT AND UPON REACHING CONTINUE DSCNT VIA THE SUNSET 1. AT 12000 FT, WE WERE ADVISED BY APCH CTL WE SHOULD BE AT 13000 FT AND TO CALL THE TRACON FOR A POSSIBLE DEV. I TALKED TO THE TRACON SUPVR WHO SAID SHE HAD LISTENED TO THE TAPE AND WOULD BE SENDING THE MATTER TO THE REGIONAL COORDINATOR TO DECIDE HOW IT SHOULD BE HANDLED. SHE ALSO SAID THERE WAS NO TFC CONFLICT. I BELIEVE THIS COULD HAVE BEEN PREVENTED BY TRAINING THE CTLRS NOT TO ISSUE AMBIGUOUS OR CONFLICTING DSCNT CLRNCS. IF THE CTLR ONLY WANTED ME TO DSND TO 13000 FT, HE SHOULD NOT HAVE PREFACED IT WITH DSND VIA THE SUNSET 1. ALSO, PLTS SHOULD NOT ACCEPT CLRNCS UNTIL THEY CLRLY UNDERSTAND THE CTLR'S INTENT.

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.