Large Transport; Low Wing; 3 Turbojet Eng
Flight Crew Commercial
Time Pressure; Workload; Confusion; Communication Breakdown
Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Human Factors; Procedure
On the SBONO Approach; Approach Control cleared us to 11;000 FT to cross CLOWD Intersection while descending around 12;000. We were within 5 miles of crossing CLOWD Intersection. The Commercial Chart actually has MAA 10;000 FT in bold letters beside the intersection on the chart but there is a faint arrow pointing the opposite direction of our flight path. I thought I heard the Controller say 'Cross CLOWD at 10;000 FT' but it was actually a clearance to cross at 11;000 FT. While the Captain was clarifying the altitude; I descended through 11;000 FT due to my descent rate and thought process of not wanting to miss the crossing restriction that was quickly approaching. The whole event lasted less than 30 seconds. There was no conflict with other traffic. We were not in a sterile period and we were not talking to each other at the time. I misunderstood the Controller. I would obviously not descend below the altitude the Captain put in the autopilot altitude window until clarifying the altitude. I would also suggest Commercial Chart publisher make changes to the approach chart and move the MAA 10;000 away from the SID course line.
An First Officer flying the PSP SBONO 1 Arrival misunderstood the Controller's 11;000 FT CLOWD crossing clearance and momentarily descended below 11;000; then returned. The Commercial Chart MAA altitude formatting at CROWD was confusing.