Narrative:

Passing bands intersection [we were] issued a heading to petis NDB; cross at 4;200 ft; intercept ILS 26L cleared for approach. Set 4;200 ft in MCP panel and verified per company procedures. Autopilot was engaged and [the] aircraft kept descending when we noticed 2;800 ft was set in altitude window. [At] about 3;200 ft MSL approach issued a low-altitude alert and issued a climbing right turn. I manually flew the maneuver; re-configured the aircraft and then we were issued a left turn to 215 degrees to intercept the ILS 26L localizer; cleared for the approach. All frequencies had been tuned and identified prior to this; including petis NDB. In retrospect; I'm not sure that petis was ever entered in the FMS due to workload. I'm not sure how or why 2;800 ft was entered in the altitude window as I distinctly remember setting 4;200 ft and verifying per company procedures. [We] landed uneventfully and contacted approach by phone. [I] spoke with [the] on-duty supervisor and was informed that we were approximately 2-3 NM south of petis and at an altitude of approximately 3;200 ft; which set off the low-altitude alert. I was told as far as they were concerned; no violation had occurred and for me to fill out the appropriate report to my company. Not cross checking all the proper entries were made in the FMS; getting the aircraft configured and flying the issued instructions and fixating on why the wrong altitude was set [2;800 ft vs. 4;200 ft]; as issued and verified. Do a better job in using all available resources; i.e.; CRM.

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Original NASA ASRS Text

Title: Air Carrier Captain reports descending below assigned altitude [4;200] prior to Petis during ILS 26L at ONT. The crew was issued a low altitude alert by ATC and vectored for another approach.

Narrative: Passing BANDS Intersection [we were] issued a heading to Petis NDB; cross at 4;200 FT; intercept ILS 26L cleared for approach. Set 4;200 FT in MCP panel and verified per company procedures. Autopilot was engaged and [the] aircraft kept descending when we noticed 2;800 FT was set in altitude window. [At] about 3;200 FT MSL Approach issued a low-altitude alert and issued a climbing right turn. I manually flew the maneuver; re-configured the aircraft and then we were issued a left turn to 215 degrees to intercept the ILS 26L LOC; cleared for the approach. All frequencies had been tuned and identified prior to this; including Petis NDB. In retrospect; I'm not sure that Petis was ever entered in the FMS due to workload. I'm not sure how or why 2;800 FT was entered in the altitude window as I distinctly remember setting 4;200 FT and verifying per company procedures. [We] landed uneventfully and contacted Approach by phone. [I] spoke with [the] on-duty supervisor and was informed that we were approximately 2-3 NM south of Petis and at an altitude of approximately 3;200 FT; which set off the low-altitude alert. I was told as far as they were concerned; no violation had occurred and for me to fill out the appropriate report to my company. Not cross checking all the proper entries were made in the FMS; getting the aircraft configured and flying the issued instructions and fixating on why the wrong altitude was set [2;800 FT vs. 4;200 FT]; as issued and verified. Do a better job in using all available resources; i.e.; CRM.

Data retrieved from NASA's ASRS site as of April 2012 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.