Narrative:

We were assigned descend via the TAMMY4 RNAV arrival. Began the arrival and we were vectored off of it and given a speed which was slower than the arrival speed; then reassigned direct to tammy and published speeds. Began the descent and became focused on flying the arrival and watching for the snowflake because we didn't know when it would show or disappear. Our filed altitude was FL180. As we began the descent out of FL180 we forgot to set the alt and complete the descent and approach check. The altimeter setting was 30.34. We had briefed the approach plenty early and were prepared for the arrival. We may have missed some of the above and or below crossing restrictions on the arrival due to the wrong altimeter setting. Before reaching the final alt on the arrival of 4;000 ft we were told to disregard all further crossing restrictions and descend to 2;000 ft. On the descent to 2;000 ft the pilot not flying noticed that we had not set the altimeter to the correct settings. We quickly reset them and ran a descent and approach to make sure everything was accomplished. Threats were; the complicated and task laden RNAV arrivals with an aircraft with very limited VNAV capabilities; 9 hour overnight in which I got probably about 6 hours of sleep; not seeing the altimeter setting blink on the pfd because we were filed at FL180; hearing other company receive odd clearances by ATC for a GPS approach which we do not have in our charts because the ILS is not working for 18R/36L. The error was not catching that we did not have the altimeter settings correct. Undesired state was the possibility that we may have been above some of the altitudes on the arrival that have between altitudes depicted on the charts. We are not actually sure if we missed any of them but there is the possibility. The need to constantly watch the 'snowflake' and guess at what descent rates are needed and worry about if you are going to be able to slow for the next crossing if you actually follow it (which you will not unless you dive below it) distracted us from doing the descent and approach check. Being at FL180 and starting the arrival from there also contributed to us missing it. The company needs to talk to the FAA more about these arrivals and work out better ways that are less task intensive for the pilots at critical times. This is especially important when our aircraft are not equipped with tools to reduce this workload to an always manageable level. They may work in a simulator but when used in practice with tailwinds and other distractions they become overwhelming without autothrottles and an FMS that gives you an indication of where to slow and level off other than a disappearing 'snowflake'.

Related reports:

Google
 

Original NASA ASRS Text

Title: CRJ-200 Captain reported deviating from the charted MEM TAMMY4 RNAV arrival; citing aircraft vertical navigation limitations and fatigue as contributing.

Narrative: We were assigned descend via the TAMMY4 RNAV arrival. Began the arrival and we were vectored off of it and given a speed which was slower than the arrival speed; then reassigned direct to TAMMY and published speeds. Began the descent and became focused on flying the arrival and watching for the snowflake because we didn't know when it would show or disappear. Our filed altitude was FL180. As we began the descent out of FL180 we forgot to set the alt and complete the descent and approach check. The altimeter setting was 30.34. We had briefed the approach plenty early and were prepared for the arrival. We may have missed some of the above and or below crossing restrictions on the arrival due to the wrong altimeter setting. Before reaching the final alt on the arrival of 4;000 FT we were told to disregard all further crossing restrictions and descend to 2;000 FT. On the descent to 2;000 FT the pilot not flying noticed that we had not set the altimeter to the correct settings. We quickly reset them and ran a descent and approach to make sure everything was accomplished. Threats were; the complicated and task laden RNAV arrivals with an aircraft with very limited VNAV capabilities; 9 hour overnight in which I got probably about 6 hours of sleep; not seeing the altimeter setting blink on the PFD because we were filed at FL180; hearing other company receive odd clearances by ATC for a GPS approach which we do not have in our charts because the ILS is not working for 18R/36L. The error was not catching that we did not have the altimeter settings correct. Undesired state was the possibility that we may have been above some of the altitudes on the arrival that have between altitudes depicted on the charts. We are not actually sure if we missed any of them but there is the possibility. The need to constantly watch the 'snowflake' and guess at what descent rates are needed and worry about if you are going to be able to slow for the next crossing if you actually follow it (which you will not unless you dive below it) distracted us from doing the descent and approach check. Being at FL180 and starting the arrival from there also contributed to us missing it. The Company needs to talk to the FAA more about these arrivals and work out better ways that are less task intensive for the pilots at critical times. This is especially important when our aircraft are not equipped with tools to reduce this workload to an always manageable level. They may work in a simulator but when used in practice with tailwinds and other distractions they become overwhelming without autothrottles and an FMS that gives you an indication of where to slow and level off other than a disappearing 'snowflake'.

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.