Narrative:

Prior to beginning the ravnn 6 arrival into bwi (we had thoroughly briefed the descent and arrival well before our initial descent) we were given several step-down altitude changes as well as speed restrictions and off-profile vectors. As we began the descent; we were then re-cleared direct fzeek to continue the RNAV arrival. About this time the pm went off VHF COMM1 to talk to the flight attendants regarding the potential for turbulence in the descent and to clean up the cabin now and call us when seated; we will make normal 10;000 ft notification; etc. So for a period of time I was essentially a single-seat pilot. The combination of multiple off-profile headings; altitude changes; and speed requirements; along with weather concerns and ongoing lack of confidence in the FMC software to accurately 'catch up' in a dynamic environment; all caused my situational awareness to degrade. I was clearly in the 'yellow' to the point I had to revert automation from FMC mode to MCP mode; and eventually to cws; in attempts to ascertain where we were laterally and vertically on the descent profile. All of which caused me to miss the FL230 altitude restriction at fzeek. Once back on VHF COMM1; the pm did an excellent job of communicating with ATC to report the altitude error and in assisting me getting us back on the arrival profile and back into FMC automation for the remainder of the arrival (although ATC made further modifications to the arrival). Conversation with ATC indicated they were not concerned about our altitude error; however; I am submitting this report (I believe the first officer will also report) in order to highlight a safety concern of the continuing trend of ATC severely modifying already intricate arrival procedures thus significantly increasing crew task loading; reducing situational awareness; and adding unnecessary (in many cases) risk.1. Better crew coordination in timing of conversations with flight attendants (however; the pm's pro-active approach in light of recent crew injury emphasis seemed appropriate; as he had no indication of further off-profile clearances). 2. Better information availability on the reliability and quality of FMC software. Many pilots I've flown with have commented that our FMC's do not operate as reliably as those they have used in previous aircraft flown. 3. Better standardization from ATC regarding published arrivals. It seems pointless to establish; publish; train; brief; and be cleared for RNAV arrivals if the likelihood of flying them as published is minimal. This did not seem to be a busy arrival (I realize there are other arrivals at multiple airports in the washington dc area); yet the number of revisions in a dynamic situation seemed unreasonable. Also; once vectored off a profile or given airspeed or altitude changes after established in VNAV path; it should be ATC's responsibility for separation for the remainder of the descent profile.

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Original NASA ASRS Text

Title: B737-800 Captain reported missing a crossing altitude on the RAVNN 6 Arrival into BWI citing ATC changes to the procedure as a factor in the incident.

Narrative: Prior to beginning the RAVNN 6 Arrival into BWI (we had thoroughly briefed the descent and arrival well before our initial descent) we were given several step-down altitude changes as well as speed restrictions and off-profile vectors. As we began the descent; we were then re-cleared direct FZEEK to continue the RNAV Arrival. About this time the PM went off VHF COMM1 to talk to the Flight Attendants regarding the potential for turbulence in the descent and to clean up the cabin now and call us when seated; we will make normal 10;000 ft notification; etc. So for a period of time I was essentially a single-seat pilot. The combination of multiple off-profile headings; altitude changes; and speed requirements; along with weather concerns and ongoing lack of confidence in the FMC software to accurately 'catch up' in a dynamic environment; all caused my situational awareness to degrade. I was clearly in the 'Yellow' to the point I had to revert automation from FMC mode to MCP mode; and eventually to CWS; in attempts to ascertain where we were laterally and vertically on the descent profile. All of which caused me to miss the FL230 altitude restriction at FZEEK. Once back on VHF COMM1; the PM did an excellent job of communicating with ATC to report the altitude error and in assisting me getting us back on the arrival profile and back into FMC automation for the remainder of the arrival (although ATC made further modifications to the arrival). Conversation with ATC indicated they were not concerned about our altitude error; however; I am submitting this report (I believe the FO will also report) in order to highlight a safety concern of the continuing trend of ATC severely modifying already intricate arrival procedures thus significantly increasing crew task loading; reducing situational awareness; and adding unnecessary (in many cases) risk.1. Better Crew Coordination in timing of conversations with Flight Attendants (However; the PM's pro-active approach in light of recent crew injury emphasis seemed appropriate; as he had no indication of further off-profile clearances). 2. Better information availability on the reliability and quality of FMC software. Many pilots I've flown with have commented that our FMC's do not operate as reliably as those they have used in previous aircraft flown. 3. Better standardization from ATC regarding published arrivals. It seems pointless to establish; publish; train; brief; and be cleared for RNAV arrivals if the likelihood of flying them as published is minimal. This did not seem to be a busy arrival (I realize there are other arrivals at multiple airports in the Washington DC area); yet the number of revisions in a dynamic situation seemed unreasonable. Also; once vectored off a profile or given airspeed or altitude changes after established in VNAV PATH; it should be ATC's responsibility for separation for the remainder of the descent profile.

Data retrieved from NASA's ASRS site 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.