B747 Undifferentiated or Other Model
Flight Crew Last 90 Days 120; Flight Crew Total 20000; Flight Crew Type 500
Confusion; Communication Breakdown
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Human Factors
On BDEGA arrival a few miles prior to CORKK. Cleared the '28L transition' and told to expect a visual to 28L. First Officer (FO) leveled at 11;000 feet to cross CORKK at 11;000 feet; then requested 1;800 feet; in the altitude window; explaining that 'the 28L transition' meant we could descend further; apparently to get down so as to be ready for a short turn on to final. There was some discussion but then we went on to other things. Shortly after descending through 10;000 feet the controller questioned our altitude and then asked us to level off at 9;000 feet. He further explained that it was no problem this time; but for future reference 'cleared the 28L transition' meant to stay at 11;000 feet and fly the 140 course out of BRIXX.
After multiple calls to ATC about our cleared arrival we convinced ourselves that we were also cleared to descend. Passing 9;800 feet MSL ATC asked where we were going; we were cleared originally to 10;000 feet. We were recleared to 9;000 feet MSl then immediately cleared to 6;000 feet MSL so obviously no loss of separation occurred.
B747 flight crew confuses a cleared via the BDEGA1 arrival as a clearance to descend via and starts down after crossing CORKK at 11;000 feet. NCT detects the error.