Narrative:

It was our last flight of the day; and I was getting tired. We had the marnr 3 arrival programmed in the FMS and had changed the crossing altitudes as advised in the last flight operations bulletin: marnr at 12;000 ft and rayni at 12;000 ft. We left all the other pre-programmed back calculated altitudes as they were. Before joining the arrival; the captain and I had reviewed and verified the routing and the crossing restrictions in the FMS against the arrival chart. They matched!after checking on with seattle center; we were cleared 'direct marnr; descend via the marnr 3; landing south.' the captain told me that he programmed a 1;500 FPM rate of descent to cross marnr at 12;000 ft. I verified it; programmed the #2 FMS to match the #1 FMS and dialed 6;000 ft in the altitude alerter after checking that we both had a vpath showing on our pfd's. We got a message from the FMS; indicating our top of descent alert; and the captain pushed VNAV. The autopilot captured the vpath and started the descent.approaching marnr; the autopilot initiated a level off at 12;000 ft. At about that time; I informed the captain that I was going off of comm 1 to call company for parking information. I was distracted momentarily while dialing the company frequency and copying down the information that operations gave me. When I looked up; we had already passed marnr and I noticed the autopilot was set to vs instead of VNAV and my altimeter had just dipped below 11;300 ft (about 700 ft below our crossing restriction for rayni). I also noticed that the captain no longer had a vpath on the #1 pfd. He began correcting the altitude deviation before I was able to call 'altitude' and we completed the flight without any further issues. These new FMS arrivals were not very well thought out. Although the automation was designed to reduce workload; it has actually done the opposite. It also creates a lot of opportunities for errors whenever we have to make changes. In this case; we had the alerter set for 6;000 ft for grify. Before reaching marnr we were told to expect [runway] 16C. Of course; I had already programmed the FMS for the ILS 16R. When approach told us to expect the center; I had changed the #2 FMS for the ILS 16C; but left the runway set for 16R so I wouldn't lose my vpath. The captain did not crossfill FMS 1 from FMS 2 or re-program the #1 FMS at that time. At some point when I was talking to company; he had changed the vertical mode from VNAV to vs. This means that our altitudes were no longer protected and the aircraft would have kept descending all the way down to 6;000 ft. I'm guessing that he also programmed the FMS for 16C at about the same time - that would at least explain why he no longer had a vpath.

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Original NASA ASRS Text

Title: An air carrier flight crew descending into SEA via the MARNR RNAV STAR descended below the at or above 12;000 FT restriction at MARNR. The deviation was the result of the incompatibility of the aircraft's FMS to deal with the complexities inherent in the 'state of the art' STAR.

Narrative: It was our last flight of the day; and I was getting tired. We had the MARNR 3 arrival programmed in the FMS and had changed the crossing altitudes as advised in the last flight operations bulletin: MARNR at 12;000 FT and RAYNI at 12;000 FT. We left all the other pre-programmed back calculated altitudes as they were. Before joining the arrival; the Captain and I had reviewed and verified the routing and the crossing restrictions in the FMS against the arrival chart. They matched!After checking on with Seattle Center; we were cleared 'direct MARNR; descend via the MARNR 3; landing south.' The Captain told me that he programmed a 1;500 FPM rate of descent to cross MARNR at 12;000 FT. I verified it; programmed the #2 FMS to match the #1 FMS and dialed 6;000 FT in the altitude alerter after checking that we both had a Vpath showing on our PFD's. We got a message from the FMS; indicating our top of descent alert; and the Captain pushed VNAV. The autopilot captured the Vpath and started the descent.Approaching MARNR; the autopilot initiated a level off at 12;000 FT. At about that time; I informed the Captain that I was going off of Comm 1 to call company for parking information. I was distracted momentarily while dialing the company frequency and copying down the information that Operations gave me. When I looked up; we had already passed MARNR and I noticed the autopilot was set to VS instead of VNAV and my altimeter had just dipped below 11;300 FT (about 700 FT below our crossing restriction for RAYNI). I also noticed that the Captain no longer had a Vpath on the #1 PFD. He began correcting the altitude deviation before I was able to call 'Altitude' and we completed the flight without any further issues. These new FMS arrivals were not very well thought out. Although the automation was designed to reduce workload; it has actually done the opposite. It also creates a lot of opportunities for errors whenever we have to make changes. In this case; we had the alerter set for 6;000 FT for GRIFY. Before reaching MARNR we were told to expect [Runway] 16C. Of course; I had already programmed the FMS for the ILS 16R. When approach told us to expect the center; I had changed the #2 FMS for the ILS 16C; but left the runway set for 16R so I wouldn't lose my Vpath. The Captain did not crossfill FMS 1 from FMS 2 or re-program the #1 FMS at that time. At some point when I was talking to company; he had changed the vertical mode from VNAV to VS. This means that our altitudes were no longer protected and the aircraft would have kept descending all the way down to 6;000 FT. I'm guessing that he also programmed the FMS for 16C at about the same time - that would at least explain why he no longer had a Vpath.

Data retrieved from NASA's ASRS site as of July 2013 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.