Air carrier medium large transport altitude excursion due to misunderstood clearance.

Attributes
ACN	102416
Time
Date	198901
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : bsr
State Reference	CA
Altitude	msl bound lower : 34000 msl bound upper : 35000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zoa
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Route In Use	arrival : profile descent
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 6000 flight time type : 200
ASRS Report	102416
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance
Consequence	Other
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Pilot Deviation other

Narrative:

At FL350 southeast of avenal VOR (ave) received clearance from ZOA as follows: cleared direct ave direct bsr then via big sur runway 28 profile descent to san francisco. Interpreted this to mean (comply with the profile descent). Approximately 50 southeast bsr left FL350 for 16000 as shown on the profile. Center requested our last assigned altitude. Informed them we were descending so as to comply with profile. Center informed us we were cleared to navigate the profile only and to maintain FL350. Reclred to FL260. Advised by center no conflict.

Original NASA ASRS Text

Title: ACR MLG ALT EXCURSION DUE TO MISUNDERSTOOD CLRNC.

Narrative: AT FL350 SE OF AVENAL VOR (AVE) RECEIVED CLRNC FROM ZOA AS FOLLOWS: CLRED DIRECT AVE DIRECT BSR THEN VIA BIG SUR RWY 28 PROFILE DSCNT TO SAN FRANCISCO. INTERPRETED THIS TO MEAN (COMPLY WITH THE PROFILE DSCNT). APPROX 50 SE BSR LEFT FL350 FOR 16000 AS SHOWN ON THE PROFILE. CENTER REQUESTED OUR LAST ASSIGNED ALT. INFORMED THEM WE WERE DSNDING SO AS TO COMPLY WITH PROFILE. CENTER INFORMED US WE WERE CLRED TO NAVIGATE THE PROFILE ONLY AND TO MAINTAIN FL350. RECLRED TO FL260. ADVISED BY CENTER NO CONFLICT.

Data retrieved from NASA's ASRS site as of August 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.