Citation X (C750)
Flight Crew Air Transport Pilot (ATP)
Other / Unknown
Aircraft Equipment Problem Less Severe; Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Undershoot
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance
Aircraft; Human Factors; Procedure
On the HHOOD 2 RNAV Arrival to PDX; the FMS was correctly set up and had already captured the VNAV on the descent from cruise; making several crossing restrictions on target. However; it calculated the 'at or below FL240' restriction at BAYYR as an 'at FL240'; which made it impossible to meet the 'Between 15;000 [and] 10;000' restriction at HHOOD. After passing BAYYR; the V-Bars abruptly went from a normal pitch attitude to a steep dive with increasing airspeed and excessive rate of descent. I intervened and disengaged the autopilot. Shortly after; ATC vectored us off the STAR with a heading for the localizer and a lower altitude. On the avionics side of the problem -- fix the FMS VNAV issues! On the navigation publication side of the problem; descent profiles on STARS are becoming more and more complicated with far too many 'cross between' altitude restrictions. It seems that there are so many parameters that the FMS is unable to calculate them correctly or in a way that makes for a smooth descent on a 'descend via' clearance.
On arrival to PDX on the HHOOD 2 RNAV; the VNAV was armed and the aircraft was established on the descent profile. The aircraft had the FMS 2 MEL on the leg prior due to not capturing the VNAV properly with the PFD selected on the right side. During the descent I pointed out several discrepancies on the Vpath and VS calculations on both sides. We crossed BAYYR at FL 240; the published crossing altitude is at or below FL240 and the next crossing restriction was HHOOD between 15;000 FT and 10;000 FT and a speed of 270 knots. After crossing BAYYR the command bars abruptly pitched down. The Pilot Flying intervened and regain control of the aircraft but the crossing restriction was not met. ATC inquired of our altitude and if we were on the HHOOD 2 arrival. Shortly after we were vectored to the localizer.
CE750 flight crew reports missing the BAYYR crossing restriction on the HHOOD 2 arrival to PDX due to an FMC malfunction. FMC 2 was MEL'd and FMC 1 created a hard altitude of FL240 at HHOOD making the BAYYR crossing restriction impossible.