B757 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 140; Flight Crew Total 19000; Flight Crew Type 10000
Situational Awareness; Workload; Time Pressure; Communication Breakdown; Human-Machine Interface; Distraction; Confusion
ATC Issue All Types; Inflight Event / Encounter Weather / Turbulence
General None Reported / Taken
Weather; Procedure; Human Factors; Chart Or Publication; Aircraft
While flying the Gibbz One arrival to IAD; somewhere near JIMVE we requested a deviation north of course for weather on the arrival route. ATC cleared us to deviate north and to proceed to IGGGY when possible. We were again unable to proceed to IGGGY due to weather. So; then we were cleared to MOSLE when able and to maintain 11;000 FT. At some point while we were deviating north of the arrival we were cleared to 'descend as though we were on the arrival.' At the time we were not on the arrival course; but 5 to 10 miles north for weather. We questioned the clearance but were given a frequency change to Potomac Approach and told to advise them that we were to 'descend as though we were on the arrival.' Upon contacting Approach Control we advised them of our 'descent clearance'; but that our last hard cleared altitude was 11;000 FT and that we would not be descending lower until cleared by them. The Controller cleared us to a lower altitude and we continued to IAD. These RNAV arrivals are difficult enough; requiring way too much of the pilot's attention as it is without trying to fly and comply with nonexistent fixed points in space while trying to safely deviate around weather.
When a B757 flight crew was cleared to 'descend as if you were 'descending via' the GIBBZ RNAV STAR to IAD' while; in actuality; deviating well north of the published track; then were switched over to another Controller without receiving a requested clarification as to what was expected of them the Captain refused to descend below a previously cleared hard altitude and felt compelled to submit this report.