Medium large transport descends below assigned altitude while flying STAR.

Attributes
ACN	230467
Time
Date	199301
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : smo airport : lax
State Reference	CA
Altitude	msl bound lower : 11700 msl bound upper : 12000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zhu
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	cruise other descent other
Route In Use	arrival other arrival star : star enroute airway : lax
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 150 flight time total : 15000 flight time type : 2000
ASRS Report	230467
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 150 flight time total : 2900 flight time type : 260
ASRS Report	230117
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : published procedure non adherence : clearance
Independent Detector	other controllera
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Was cleared for the sadde 4 arrival (which I had reviewed). At sadde intersection I was under the impression for some reason that we were cleared to cross bayst at 10000 ft. (The fact that I was used to doing it for 20 yrs previous on the old profile descent didn't help.) fortunately, because of the confusion going on at the time (lots of radio traffic), my descent was gradual and at 11700 ft the controller first cleared us to 11000 ft and then advised us that we had not been cleared to 10000 ft previously as I had thought. There was no conflict, and nothing more was said. However, it again points out to me that when we are real busy, one has to be extra, extra careful so as to totally eliminate any confusion. Supplemental information from acn 230117: the 2 arrs have almost identical crossing altitudes, speed restrictions, and fixes from fillmore to santa monica. However, the profile arrival restrictions are mandatory. The sadde arrival has the same restrictions, but they are restrictions we should expect to be assigned, and are not mandatory, unless assigned by ATC! As a result, the confusion and altitude deviation occurred during a busy and critical phase of flight.

Original NASA ASRS Text

Title: MLG DSNDS BELOW ASSIGNED ALT WHILE FLYING STAR.

Narrative: WAS CLRED FOR THE SADDE 4 ARR (WHICH I HAD REVIEWED). AT SADDE INTXN I WAS UNDER THE IMPRESSION FOR SOME REASON THAT WE WERE CLRED TO CROSS BAYST AT 10000 FT. (THE FACT THAT I WAS USED TO DOING IT FOR 20 YRS PREVIOUS ON THE OLD PROFILE DSCNT DIDN'T HELP.) FORTUNATELY, BECAUSE OF THE CONFUSION GOING ON AT THE TIME (LOTS OF RADIO TFC), MY DSCNT WAS GRADUAL AND AT 11700 FT THE CTLR FIRST CLRED US TO 11000 FT AND THEN ADVISED US THAT WE HAD NOT BEEN CLRED TO 10000 FT PREVIOUSLY AS I HAD THOUGHT. THERE WAS NO CONFLICT, AND NOTHING MORE WAS SAID. HOWEVER, IT AGAIN POINTS OUT TO ME THAT WHEN WE ARE REAL BUSY, ONE HAS TO BE EXTRA, EXTRA CAREFUL SO AS TO TOTALLY ELIMINATE ANY CONFUSION. SUPPLEMENTAL INFO FROM ACN 230117: THE 2 ARRS HAVE ALMOST IDENTICAL XING ALTS, SPD RESTRICTIONS, AND FIXES FROM FILLMORE TO SANTA MONICA. HOWEVER, THE PROFILE ARR RESTRICTIONS ARE MANDATORY. THE SADDE ARR HAS THE SAME RESTRICTIONS, BUT THEY ARE RESTRICTIONS WE SHOULD EXPECT TO BE ASSIGNED, AND ARE NOT MANDATORY, UNLESS ASSIGNED BY ATC! AS A RESULT, THE CONFUSION AND ALTDEV OCCURRED DURING A BUSY AND CRITICAL PHASE OF FLT.

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.