Narrative:

Cruising at FL350 fat; dumb; and tired we were told to cross [a fix] at FL310. The first officer was the pilot flying. He entered FL310 in the altitude window. We both pointed and confirmed. He entered the crossing restriction in the FMS; I confirmed and he activated. We both went back to staring out the window. I heard ATC tell someone to descend to FL310 and the first officer and I simultaneously realized we were less than a mile from the fix still at FL350. He initiated the descent; I called ATC. The controller made a couple other calls; and then told us to descend and maintain FL310 as well as a frequency change. I acknowledged and said thank you; he said no problem. The flight continued uneventfully. The fact is we flat out screwed up. We both thought we confirmed we were in VNAV. We watched the airplane closely on the remaining VNAV applications; it worked fine so I can only think we did not engage VNAV upon receiving the crossing restriction. We were both fatigued and had actually discussed taking coordinated naps about an hour prior to this happening; but neither of us did.... The first officer was sick the entire trip and not sleeping well. We had very early morning shows two days in a row. The simple fact is we didn't operate the airplane properly.

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Original NASA ASRS Text

Title: ERJ170 flight crew missed a crossing restriction after failing to activate VNAV until alerted by ATC. Captain listed fatigue as a contributing factor.

Narrative: Cruising at FL350 fat; dumb; and tired we were told to cross [a fix] at FL310. The First Officer was the pilot flying. He entered FL310 in the altitude window. We both pointed and confirmed. He entered the crossing restriction in the FMS; I confirmed and he activated. We both went back to staring out the window. I heard ATC tell someone to descend to FL310 and the First Officer and I simultaneously realized we were less than a mile from the fix still at FL350. He initiated the descent; I called ATC. The Controller made a couple other calls; and then told us to descend and maintain FL310 as well as a frequency change. I acknowledged and said thank you; he said no problem. The flight continued uneventfully. The fact is we flat out screwed up. We both thought we confirmed we were in VNAV. We watched the airplane closely on the remaining VNAV applications; it worked fine so I can only think we did not engage VNAV upon receiving the crossing restriction. We were both fatigued and had actually discussed taking coordinated naps about an hour prior to this happening; but neither of us did.... The First Officer was sick the entire trip and not sleeping well. We had very early morning shows two days in a row. The simple fact is we didn't operate the airplane properly.

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.