Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 34; Flight Crew Total 5946; Flight Crew Type 15
Communication Breakdown; Confusion; Other / Unknown
Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Undershoot; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Flight Crew Became Reoriented; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Clearance
Chart Or Publication; Company Policy; Human Factors
Aircraft was first cleared to FL270; subsequently the clearance descend via the GIBBZ2 was given and read back by the Captain. Both Pilot Flying and Pilot Monitoring did not understand that meant they could descend below FL270 via the arrival. Additionally it was briefed the GIBBZ Arrival is quite steep and drag may be needed; I queried the first observer if he agreed we were cellar via the arrival; he replied I was not paying attention. He then queried the Pilot Monitoring who said he thought it was FL270. I explained to him the decent via clearance at which point ATC was queried. They advised we were to comply with the altitude requirements on the arrival. They then issued a new altitude clearance and a heading. By the time I was able to clearly communicate to the crew we had already missed the FL250 crossing restriction at JIMVE. A contributing factor to this was the lack of intercom and boom mic for the second observer on the aircraft as I had to stand up to talk to the Pilot Monitoring clearly; additionally there is no port page annotation about the descend via clearance or the known steep arrival IAD combined with typically high tailwinds on this arrival.
Reporter was the only one of four pilots in the cockpit who initially understood the meaning of the 'descend via' clearance terminology as it is employed in the United States. Reporter stated the other three pilots were foreign and most likely trained abroad. Reporter did not comment on company training.
Air carrier Relief Pilot reported a missed altitude restriction while on the GIBBZ2 arrival to IAD. The crew misunderstood the 'descend via' phraseology.