Date: 201209
Local time of day: 1201-1800
Location: DCA.Airport, DC
Flight conditions: IMC
Weather elements / visibility: Icing
Aircraft: EMB ERJ 145 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class E ZDC
ATC / advisory: Center ZDC
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: Distraction; Human-Machine Interface; Situational Awareness; Time Pressure; Workload
Anomaly: ATC Issue All Types; Flight Deck / Cabin / Aircraft Event Other / Unknown
Result: General None Reported / Taken
Contributing factors: Aircraft; Chart Or Publication; Human Factors; Procedure
Primary problem: Human Factors

Narrative: We were descending on the FRDMM ONE RNAV STAR into DCA prior to WLLLL waypoint; were nearly finished getting set up for the approach; and had just passed below FL180 and completed the descent check. I was the PF and was working to ensure we were complying with all the altitude restrictions on that arrival.We were in and out of icing conditions which meant more frequent corrections to power settings and vertical speed commands. The First Officer was setting up the radio frequencies; loading the approach into the FMS; briefing the approach; calling in-range; and monitoring our descent.Between waypoints; several miles prior to WLLLL I had to put the automation into HDG mode so I could tune the final approach course for the LDA 19 approach into DCA. After setting the course; I reselected FMS NAV; re-engaged LNAV; and confirmed that the flight guidance captured LNAV mode. While the First Officer was briefing the approach; right around WLLLL; ATC said advised 'it looks like you are off the arrival. Proceed direct FORGT and maintain 12;000 FT.' I took a closer look and my CDI needle and noticed it was approximately one needle-width to the left. The First Officer's MFD indicated we were 0.9NM south of course.The LNAV was indeed still engaged as I had confirmed earlier; but for some reason was not tracking the course accurately enough. The winds aloft were from the south; so I don't know if the autopilot/flight guidance was overcorrecting; or if it never actually made an effort to stay on course after re-engaging LNAV; or what; but the automation was certainly set up correctly; it just wasn't tracking the course very accurately. I had the First Officer program ATC's requested course correction and the flight continued without incident.I don't like that FRDMM1 arrival; which I'm sorry to say because I pride myself on being able to handle the challenges we face; I like doing complex procedures; and I was determined not to be one of the people who bitch and moan about an arrival that requires a little bit of effort on our part. I've now flown that arrival 4 times; which isn't much; but it is enough to know it is too much workload for the limited automation we have on the 145. It requires almost constant fixation by the PF on the descent rate and airspeed; mainly because the waypoints are so close together; and the upper limit of the next waypoint is often already lower than the lower limit of the previous one.It also task saturates the PM because he must double check the PFs altitude in addition to all his or her other tasks in that phase of flight. A course deviation of a single needle-width; less than a mile; (which looks completely normal on the MFD map by the way); is obviously easy to overlook under these conditions. In the winter time; we are going to be doing this arrival with 100 KTS tailwinds; in and out of icing conditions; while possibly checking landing performance if the runways are contaminated.While the aircraft is RNAV capable and has VNAV data in the FMS; I do not believe it is safe for us to do this arrival; as an aircraft doing this arrival with full VNAV automation needs only to be monitored closely; not continuously 'flown' with the flight guidance panel and/or thrust levers and spoilers like we need to do. I may change my mind after I've flown this arrival 40 times instead of 4; but for now I recommend we either discontinue doing the arrival; or be authorized to refuse it from ATC if we believe the environmental factors or human factors (new First Officer/both pilots new to the arrival/etc.) would pose a hazard. There are too many chances to bust an altitude and cause loss of separation; and the pilot workload is too high; and something more important than being less than a mile off course could be overlooked.




Synopsis: The Captain of an ERJ 145 expressed his belief that his aircraft hasn't the VNAV sophistication required to perform the complex RNAV STARs such as the FRDMM ONE to DCA. He believes flight crew workload required to comply with crossing restrictions without full functioning VNAV/autoflight/autothrottle capability is excessive under the best of conditions. Under adverse weather and or tailwind conditions he believes compliance will require complete disregard of other flight safety considerations and may well simply overwhelm the flight crew's and aircraft's capacities.