Flight Crew Air Transport Pilot (ATP)
Workload; Human-Machine Interface; Communication Breakdown; Distraction
ATC Issue All Types; Deviation - Altitude Crossing Restriction Not Met
Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification
Procedure; Human Factors; Chart Or Publication
Washington Center held us up very high due to a B52 passing underneath us right to left. We were on the new GIBBZ1 arrival which has 9 step down fixes with speed constraints. Our FMGS reverted to a descent speed mode of .67 Mach instead of the desired .76/280. The First Officer began trying to remedy that situation while the Center gave us a descend via the GIBBZ1 arrival. We proceeded to immediately chop and drop to get back on the profile. I told ATC we were unable to comply with the altitude constraints. ATC said to cross IGGGY at or below 13;000 FT then descend via the GIBBZ1. We crossed IGGGY at approximately 12;300 FT and were supposed to cross MOSLE at 11;000 FT and 250 KTS. I thought the First Officer was going to go back to managed descent but she stayed in selected descent and was trying to get the aircraft slowed to 250 KTS at MOSLE. By staying in selected descent we crossed MOSLE at 10;600 FT instead of 11;000 FT. We then reverted back to managed descent mode for the rest of the arrival and there were no further problems.ATC basically set us up for problems on the brand new arrival with the late descent as a descend via clearance with no possible way for us to make the points. The First Officer also spent too much time heads down trying to change the desired speed in the FMGS instead of just selecting 280 KTS. There are so many different altitude windows and descent points with various types of descent criteria (between altitudes; at altitudes; at or below altitudes) that if you are very rushed like we were; it is very difficult to determine which one you are not going to make. This arrival has fixes that are very close together and will work in a managed descent mode only if everything works perfect from the beginning of the arrival. If ATC leaves you high (this sector of Washington Center is notorious for just that); then they are setting the Airbus crews up for mistakes. In the future; I will insist that this arrival be flown in selected speed and managed descent to avoid any confusion with the FMGS descent mode. Any other way just leaves too many ways to get confused and cause errors.
When they received a late 'descend via' clearance on the GIBBZ RNAV STAR to IAD; the flight crew of an A319 was unable to comply with the multiple altitude and airspeed restrictions and required ATC re-clearances to complete the arrival; citing the complexity of programming changes in a manner that satisfies the restrictions and the capabilities of the aircraft and the FMGS.