Narrative:

We were flying a VNAV capable -300. We received a restriction to be at 12;000 ft and 250 KTS at a waypoint on the RNAV STAR ([cleared to] descend via the arrival). I had to switch from VNAV to vertical speed due to the fact that the airplane responded in a rough manner in the VNAV mode and got off profile. I (the pilot flying) had to keep track of the restrictions by looking at the captain's CDU as he was getting the weather on my CDU. Due to a glare; I had a hard time seeing the legs page on the captain's CDU and subsequently believed that I saw that I met the restriction at the fix after which I continued the descent. However; when I looked several seconds later; I thought I saw the legs page switch to the next fix; which would mean I went through the 12;000 ft restriction too early. I just could not see it well enough to say with 100% certainty whether or not I had an altitude deviation. ATC did not say anything; but just to be sure; I elected to file a report and advised my captain to do the same.these aircraft need to get the needed equipment so that a captain does not have to work on my side; and I don't have to use the equipment on his side. VNAV in a -300 without autothrottles really does not work well. We should either implement the systems needed completely; or not at all. Next time I should interrupt the pilot not flying in his tasks and ask for his help/eyes to confirm if what I think I am seeing is reality or not.

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Original NASA ASRS Text

Title: A B737-300 First Officer reported a possible failure to meet a crossing restriction on an RNAV STAR. He believed the rudimentary FMS installed in some of the air carrier's -300 fleet fail to provide flight crews with the access to information to allow it to be used reliably.

Narrative: We were flying a VNAV capable -300. We received a restriction to be at 12;000 FT and 250 KTS at a waypoint on the RNAV STAR ([cleared to] descend via the arrival). I had to switch from VNAV to Vertical Speed due to the fact that the airplane responded in a rough manner in the VNAV mode and got off profile. I (the pilot flying) had to keep track of the restrictions by looking at the Captain's CDU as he was getting the weather on my CDU. Due to a glare; I had a hard time seeing the LEGS page on the Captain's CDU and subsequently believed that I saw that I met the restriction at the fix after which I continued the descent. However; when I looked several seconds later; I thought I saw the LEGS page switch to the next fix; which would mean I went through the 12;000 FT restriction too early. I just could not see it well enough to say with 100% certainty whether or not I had an altitude deviation. ATC did not say anything; but just to be sure; I elected to file a Report and advised my Captain to do the same.These aircraft need to get the needed equipment so that a Captain does not have to work on my side; and I don't have to use the equipment on his side. VNAV in a -300 without autothrottles really does not work well. We should either implement the systems needed completely; or not at all. Next time I should interrupt the pilot not flying in his tasks and ask for his help/eyes to confirm if what I think I am seeing is reality or not.

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.