Date: 201409
Local time of day: 0001-0600
Location: ZDC.ARTCC, VA
Flight conditions: VMC
Aircraft: B757 Undifferentiated or Other Model
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
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Human factors: Human-Machine Interface
Second reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Undershoot; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Became Reoriented; Flight Crew Overcame Equipment Problem; Flight Crew Returned To Clearance
Contributing factors: Aircraft; Weather
Primary problem: Ambiguous

Narrative: While on the GIBBZ TWO RNAV ARRIVAL for Washington DC (VA) after passing TABBE on the high side of its altitude window and VNAV PATH displayed and also had the lowest altitude for the STAR set in the altitude window. At about FL195; pilot monitoring (PM) recognizing that the ATC altimeter from ATC was 30.28 (High) that we would be proactive in getting that set with no delay. And did so. PM went heads down and requested the latest ATIS so as to verify and have the latest altimeter. Also a call from the cabin came at about this time and the PM answered it and had a short conversation. PM then accepted and printed the ATIS and announces the altimeter at airport would be 30.30 Inches. The PM then returned to monitoring the pilot flying (PF); at this time the PM noticed that it appeared we were going to be high for the next crossing (KIKKR) yet while still in VPATH. The PM asked the PF to confirm this and then instructed the PF to take immediate corrective action. PM was still not satisfied with the aggressiveness of the corrective action and asked the PF to disconnect the autopilot and use full speed brake and push the nose over to get back on VPATH; which the PF did. It would be reasonable to conclude we were high at KIKKR but back on VPATH for the next fix which was IGGGY. Just past IGGGY ATC radioed us to turn to a heading for vectors for a Visual Approach. There was no conversation with ATC reference our arrival and went on to land uneventful. PM and PF debriefed at the gate and discussed this STAR. We both felt the VNAV PATH was very subtle in its inability to not maintain the path and was a surprise to us considering that we were on path from the very first fix and on speed with no changes from ATC. We thought the issue involved the high altimeter setting combined with slow technology of the FMC in conjunction with crossing the initial STAR fixes on the high side. Obviously we are not happy with the result.


Second narrative: While on the GIBBZ arrival to IAD we crossed TABBE at approximately FL190 on speed and set our altimeter while in the descent to 30.28; We noticed we might be high by KIKKR and put full speed brakes out and kicked off the autopilot; the VNAV Path showed us on the descent path but we were high by up to about 1;000 foot; by IGGGY we were back on the descent path on altitude and speed. We were then given a 150 degree heading for vectors to runway 1R and continued for the approach and landing. The plane always showed on path but the aircraft was high at KIKKR.


Synopsis: B757 Flight Crew reports crossing KIKKR high during the GIBBZ arrival to IAD. The local altimeter setting of 30.30 was set passing FL190 and the FMC path shown on profile while crossing KIKKR 1;000 feet high.