Date: 201209
Local time of day: 0601-1200
Location: MEM.TRACON, TN
Aircraft: Regional Jet 200 ER/LR (CRJ200)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Descent
Aircraft component: FMS/FMC
Component problem: Design
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Commercial
Human factors: Situational Awareness; Communication Breakdown; Distraction; Human-Machine Interface; Workload
Second reporter function: Pilot Flying; Captain
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Chart Or Publication; Human Factors; Procedure; Aircraft
Primary problem: Ambiguous

Narrative: While enroute to MEM we were cleared to descend via the TAMMY RNAV STAR; North transition. I read back the clearance and then the Captain questioned ATC about the speed and altitude restrictions over TAMMY and ROCAB. ATC verified the fixes/altitudes/speeds on the arrival and we completed our briefing. Since the Captain had already questioned ATC himself; I understood that he had heard the 'descend via' instruction and was complying. (The Captain had not participated in any RNAV arrivals into MEM before but we had gone over them the day before.)As I was about to question him; ATC came back and was asking what we were assigned. I responded that we were assigned the descend via Tammy 4. She questioned repeatedly and I answered and then we were reassigned a heading. We continued into MEM with no other complications and were asked to call ATC when we got on the ground. The call was placed and they just wanted to go over what had happened and were requesting further information since the RNAV arrivals have had problems.We should always confirm the 'descend via' read back. Also the RNAV's into MEM plates are very small and jumbled. I think having the pull out pages and more to scale spacing would help greatly. I know I am constantly cross-checking with the FMS and plate when I fly the RNAV's because there are so many different options and routes crammed into the small page. Also; maybe hard altitudes [should be charted] instead of all the [above/below] variances. We were at an appropriate speed and altitude at TAMMY but with ROCAB only two miles away; I did not have time to correct the Captain.


Second narrative: While we were on a heading from the previous controller; Approach Control cleared us to proceed Direct TAMMY for the 'North Transition'. We were confused as to what the controller meant by 'North Transition': was it to set ROCAB or the arrival all the way to SKEEZ. [Because I was] trying to figure that out I was late selecting VNAV. The controller came back and gave us a 150 heading to go direct TAMMY and we did. I was so hung up on what exactly to load in the FMS after TAMMY that I never heard the controller give us a descend via the TAMMY arrival. We were at 15;000' which was an acceptable altitude at TAMMY ('Between 16000' and 10000'). I got on the radio and asked the controller if the next waypoint after TAMMY for the North Transition was ROCAB at 230 Knots and 10;000. Controller said yes; ROCAB 230 knots and 10;000. The way the controller answered my question sounded like we were just confirming the waypoint and the waypoint altitude and speed; which was on the same tone I asked the question: just as a confirmation for the direction to go after TAMMY. We kept approaching TAMMY and about a mile or so before it we were switched to the next Controller who asked us if we were given an assigned altitude. PM replied: no. I had already told the PM to ask if they wanted us to cross ROCAB at 230 and 10;000 but there are only 2 miles from TAMMY to ROCAB and by the time the controller was done asking us if we were assigned an altitude; my FO did not have time to ask what I told her because we were basically over TAMMY and by the end of the transmission we were over ROCAB. The controller then gave us a 090 heading and a descend to 6;000. The rest of the flight went smoothly.There were no crazy turns or abnormal descents. Everything went smooth besides the confusion as to the crossing altitudes.It seems absurd to me to have an arrival; like TAMMY; with so many above and below restrictions. It has to be crossed A10;000 but B16000 and then if you are at 16;000 they expect you to cross ROCAB at 10;000. Why don't they just force people to cross TAMMY at 10;000 or at least a reasonable altitude to be able to make ROCAB at 10;000. The approach plate page should be bigger. It is so cramped it is hard to read. There is no clear explanation as to what is the North Transition as SKEEZ also goes to the North. This needs to be more detailed. The snowflake won't come up if the altitudes say between so and so or even if it says 10;000A or 10;000B. On waypoints like that the PF should be able to modify the FMS entry and input an altitude that satisfies the crossing restriction; get rid of the above or below in order to get the snowflake. The biggest problem here was that nothing stated clearly what a North Transition was. Next time I will double or triple check to make sure if we have been cleared to descend via or not as a precautionary measure.

Second callback: The Captain stressed his two concerns over ATC's use of the phrase 'North [or; likely; South when appropriate] Transition' when clearing flights via the STAR.  First; that there is no mention of any 'Transition' on the STAR chart (the two tracks after TAMMY are not technically 'line selectable' transitions but are displayed as the appropriate route when the runway of intended landing is programmed); and; second; the phrase logically directs the flight crew to expect the 'North Transition' to be the track that actually goes 'to the North' in order to 'land to the south' and vice versa.He further advised that the capabilities of the FMS/Autoflight/VNAV system in his aircraft are not compatible with the complexities of the crossing windows commonly employed in the recently published complex/optimized STAR procedures.  Because there are no autothrottles installed; there is no 'sophisticated; FMS generated; flight path guidance' available for the flight crew to monitor 'down the road' compliance and optimization of actual crossing altitudes within the restriction windows.  In their aircraft; optimal vertical path guidance can only be achieved by intense monitoring and manual power/vertical path control by the flight crew.  Doing so requires mentally starting from the final crossing restriction and working backwards through each 'window' to determine--and control the flight path to obtain--the optimal actual crossing; a hugely burdensome workload on the pilots.TAMMY is a good example of that problem.  The 10000' foot bottom crossing is compatible with landing 'to' the North and the 16000' top crossing with landing 'to' the South.  If; however; a 'North' landing flight crosses TAMMY anywhere above 10000 feet (and at or very near 250K) there is no way to cross ROCAB at 10000 and 230K.He suggests more appropriate phraseology by ATC (i.e. '...cleared via the TAMMY STAR/ROCAB' for instance) and a revision to the chart to state 'cross TAMMY at 16000' when landing South' and '...at 10000' when landing North'.

Synopsis: A CRJ-200 Flight Crew addressed their concerns about ATC phraseology and their aircraft's autoflight system's capability to cope with the more complex aspects of the TAMMY RNAV STAR to MEM.