Narrative:

We were on the TAMMY4 arrival eld transition into mem. We were given a 'descend via' clearance. Everything was going fine until the descent to cross tammy between 16;000 and 10;000 ft; followed 2 miles later by rocab at 10;000 ft and 230 KTS. Three things happened in fairly quick succession that contributed to me missing the crossing restriction. I was looking at the vertical guidance supplied on the mfd (the green data) and it was showing the descent rate that I was currently doing. It didn't seem right so I did some mental math and increased my descent rate also checking for the snowflake which wasn't showing (found out later that it had fallen out when the FMS had briefly gone into roll mode).then ATC gave us a runway change which distracted us and when we had answered we both realized that we would not make the crossing restriction and notified ATC immediately. I believe the root of the problem was that: 1) I didn't realize the snowflake was disabled; 2) I originally thought the green VNAV info on the mfd would give me the bottom of the 16;000 to 10;000 ft envelope since rocab is so close to tammy and 3) I was distracted with the runway change and lost awareness for enough time to not make the restriction. Contributing factors included: hurrying because we had been delayed; there were new arrivals in memphis--this was our first time on this arrival landing to the north; some weather deviations; and an early morning report for duty. Our errors included: not remembering that the snowflake will become disabled if the aircraft goes into the roll mode; not catching that the snowflake wasn't coming up because it was disabled; not using the range to altitude (banana bar) to it's fullest extent; not holding off on worrying about the runway change until past the crossing restriction; not realizing that the green VNAV data on the mfd wouldn't necessarily give me the bottom of the altitude envelope at tammy even with rocab being so close; finally; not backing up the automation with good old math. As a result we crossed rocab on speed but about 4;000 ft high. I do not believe that our briefing was to blame because we completely briefed and cross checked the arrival with the FMS but the automation was where I made my mistake. In the future I will make sure that the primary sources for descending via an arrival are the snowflake and mental math--not the green mfd VNAV--because that is giving information for the next fix only and with an altitude block not necessarily the bottom of said block.

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Original NASA ASRS Text

Title: While flying the TAMMY RNAV STAR to land North at MEM; the flight crew of a CRJ-200 arrived at TAMMY too high to make the crossing restriction of 10;000 FT and 230 KTS at ROCAB; only two miles beyond TAMMY.

Narrative: We were on the TAMMY4 arrival ELD transition into MEM. We were given a 'descend via' clearance. Everything was going fine until the descent to cross TAMMY between 16;000 and 10;000 FT; followed 2 miles later by ROCAB at 10;000 FT and 230 KTS. Three things happened in fairly quick succession that contributed to me missing the crossing restriction. I was looking at the vertical guidance supplied on the MFD (the green data) and it was showing the descent rate that I was currently doing. It didn't seem right so I did some mental math and increased my descent rate also checking for the snowflake which wasn't showing (found out later that it had fallen out when the FMS had briefly gone into roll mode).Then ATC gave us a runway change which distracted us and when we had answered we both realized that we would not make the crossing restriction and notified ATC immediately. I believe the root of the problem was that: 1) I didn't realize the snowflake was disabled; 2) I originally thought the green VNAV info on the MFD would give me the bottom of the 16;000 to 10;000 FT envelope since ROCAB is so close to TAMMY and 3) I was distracted with the runway change and lost awareness for enough time to not make the restriction. Contributing factors included: hurrying because we had been delayed; there were new arrivals in Memphis--this was our first time on this arrival landing to the North; some weather deviations; and an early morning report for duty. Our errors included: not remembering that the snowflake will become disabled if the aircraft goes into the roll mode; not catching that the snowflake wasn't coming up because it was disabled; not using the range to altitude (banana bar) to it's fullest extent; not holding off on worrying about the runway change until past the crossing restriction; not realizing that the green VNAV data on the MFD wouldn't necessarily give me the bottom of the altitude envelope at TAMMY even with ROCAB being so close; finally; not backing up the automation with good old math. As a result we crossed ROCAB on speed but about 4;000 FT high. I do not believe that our briefing was to blame because we completely briefed and cross checked the arrival with the FMS but the automation was where I made my mistake. In the future I will make sure that the primary sources for descending via an arrival are the snowflake and mental math--not the green MFD VNAV--because that is giving information for the next fix only and with an altitude block not necessarily the bottom of said block.

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.