Date: 201207
Local time of day: 0601-1200
Location: MEM.Airport, TN
Light: Daylight
Aircraft: Regional Jet 200 ER/LR (CRJ200)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Descent
Airspace: Class E MEM
ATC / advisory: TRACON M03
Aircraft component: FMS/FMC
Component problem: Design
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Situational Awareness; Human-Machine Interface; Fatigue; Confusion
Second reporter function: First Officer; Pilot Not Flying
Anomaly: ATC Issue All Types; Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Undershoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Aircraft; Chart Or Publication; Human Factors; Procedure
Primary problem: Aircraft

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.

Callback: The Captain advised she had been commuting into MEM on another air carrier jump seat shortly after this event and was told that carrier had bulletined the flight crews not to accept the TAMMY arrival because of the same issue; the FMS' failure to 'look ahead' to the more restrictive fix and instead simply provide guidance to the higher altitude in the 'crossing window.'

Second narrative: On descent into MEM we were assigned to descend via the TAMMY ONE arrival. The Captain placed 10;000 FT in the altitude alerter so that we would have vertical guidance on the way down. Approaching TAMMY Intersection to cross between 16;000 and 10;000 FT we noticed that we were going to be too high to cross ROCAB Intersection at 10;000 FT. We immediately advised ATC and were told that it was no problem and to further descend for the approach into MEM. The descent info provided to us via the green descent box on the MFD only gave us descent info to reach TAMMY at 16;000 and not ROCAB at 10;000 FT.We believe the major contributing factor to this event was the complexity and vagueness of the arrivals into MEM. The descent info provided to the crew was inaccurate due to the FMS wanting to cross TAMMY at 16;000 and not ROCAB at 10;000 FT. These arrivals are unlike any descend via's I have flown as they allow too much leeway and too many areas to mess up. Also on the MFD the Green Attitude information next to TAMMY Intersection seems to cover up the altitude information next to ROCAB. These charts are difficult to read as well and with the controllers having issues as well it is causing a much higher workload than should be required to achieve a successful outcome.

Second callback: The First Officer advised the fleet utilizes a Collins FMS but was unaware of the exact model. He also suggested there were ongoing anomalies and/or 'unfamiliarities on the part of the flight crews' with the operation of the system that have gone unaddressed by either the manufacturers or the airline. He was 'reasonably certain' that any runway change they received was simply another northbound runway parallel to the one in their original clearance and not 'from a southbound to a northbound' runway that would have affected the necessary altitude at which they would have had to cross TAMMY to meet the restrictions at ROCAB. He clarified the 'snowflake' as being a descent path indicator similar to a glideslope which; had it been activated; should have shown their relationship to the vertical path necessary to meet the crossing at ROCAB. The 'banana bar' provides the point along their LNAV path where they would reach the altitude in their altitude alerter. He further advised the aircraft is not equipped with autothrottles which makes flight crew awareness of their descent path more critical in that full VNAV autoflight capability is not available. This lack also illuminates why the presence of the 'snowflake' becomes a critical factor.

Synopsis: 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.