Narrative:

The first officer was flying. He told me he had just over 100 hours in the airplane. Passing sli VOR we were given a heading of 300; maintain 3600 feet until on final approach course; then cleared a visual approach for runway 25L. We were tracking outside of hunda at 210 kts. The first officer had the FMS set up in green VNAV (no altitude protection). I questioned him if that is what he really wanted. He said; 'yes.' while on base leg he asked me to set 1900 feet in the altitude alerter. I asked him did he really want that now and he said; 'yes.' I reminded him of the 3600 foot altitude restriction until on final approach course intercept. Anyway; he blew through the 3600 assigned altitude on base leg. He was so confused that captain had to take the airplane and return the airplane to 3600 feet as he let the airplane continue to descend. The captain was telling him to get the autopilot off and return to 3600 feet. I think the first officer at this point was in a zone of automation confusion.the first officer seemed to be nervous or maybe not fully confident in his abilities. He asked me to fly the prior leg. I have never flown with this first officer. The first officer did a satisfactory job flying from ZZZ to the sli VOR. The first officer's background is that of a traffic watch helicopter pilot. It seemed that he may have been confused regarding the FMS; the various autopilot modes; letting the airplane get ahead of him; etc.the first officer will need to be monitored (I have already let my chief pilot know about this unfortunate incident). Hopefully; he can be given some more training/IOE or a line check. The first officer knows he made a mistake.

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Original NASA ASRS Text

Title: EMB-175 Captain reported the First Officer's mismanagement of the FMC and altitude alerter resulted in descending through an altitude restriction.

Narrative: The First Officer was flying. He told me he had just over 100 hours in the airplane. Passing SLI VOR we were given a heading of 300; maintain 3600 feet until on Final Approach Course; then cleared a Visual Approach for RWY 25L. We were tracking outside of HUNDA at 210 kts. The First Officer had the FMS set up in green VNAV (no altitude protection). I questioned him if that is what he really wanted. He said; 'YES.' While on base leg he asked me to set 1900 feet in the altitude alerter. I asked him did he really want that now and he said; 'YES.' I reminded him of the 3600 foot altitude restriction until on final approach course intercept. Anyway; he blew through the 3600 assigned altitude on Base Leg. He was so confused that Captain had to take the airplane and return the airplane to 3600 feet as he let the airplane continue to descend. The Captain was telling him to get the autopilot off and return to 3600 feet. I think the First Officer at this point was in a zone of automation confusion.The First Officer seemed to be nervous or maybe not fully confident in his abilities. He asked me to fly the prior leg. I have never flown with this First Officer. The FO did a satisfactory job flying from ZZZ to the SLI VOR. The First Officer's background is that of a Traffic Watch Helicopter Pilot. It seemed that he may have been confused regarding the FMS; the various autopilot modes; letting the airplane get ahead of him; etc.The First Officer will need to be monitored (I have already let my Chief Pilot know about this unfortunate incident). Hopefully; he can be given some more training/IOE or a Line Check. The First Officer knows he made a mistake.

Data retrieved from NASA's ASRS site 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.