Flight Crew Air Transport Pilot (ATP)
Flight Crew Type 36
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Human Factors
During my preflight inspection; while setting the landing altitude in the pressurization panel; I set what I thought was 20 feet for landing. I noticed something looked odd; but couldn't really identify what was out of place. As far as I knew; there are only 4 available digits; so I set 0020.After leveling off and cruising at FL370 for 11 minutes we got a cabin pressure warning. After donning the O2 mask; we started to diagnose the problem. The cabin altitude was steady at 10;000. Shortly after that it finally dawned on me what had previously looked odd about the landing altitude selector. There are not 4 digits; but rather 5 on the selector. The first rotating digit is significantly wider than the following 4 (about 1 inch wide vs an 1/8 of an inch). I had assumed it was stationary; but it's not. When I started the preflight the 10;000 digit was already displayed. So as I rotated the elevation down; I unknowingly stopped at 10;020 feet instead of 0020 feet.Needless to say the pressurization panel worked as advertised. We set 0020 and the pressurization returned to normal. As a precaution we requested clearance to descend to FL330 while the pressurization stabilized. After coordination with Dispatch and Maintenance; we returned to FL370 and continued to destination.My failure to originally trap the error during the preflight cannot be overstated. I take full responsibility for the error and it certainly is a lesson learned. My only questions and concerns for future crews is; why was the controller set above 10;000 feet in the first place? There's no operational reason to do so; since the highest fleet wide landing limitation is 9;500 feet. Is there some maintenance check that requires it? If not; why is there even a 10;000 digit; if it can't be used? Lastly; since there obviously is a 10;000 digit; why is it not consistently labeled as the following digits? The 10;000 digit is either blank or 1. In other words; to set 20 feet you currently set (blank;0;0;2;0). If it were consistent; you would set (0;0;0;2;0).Bottom line; lesson learned; won't happen again.
B757 First Officer reported incorrectly setting the landing altitude in the pressurization panel; resulting in a cabin pressure warning which was rectified after the correct landing altitude was entered.