Date: 201510
Local time of day: 0601-1200
Location: COS.Airport, CO
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Cessna Citation Sovereign (C680)
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class A ZDV
ATC / advisory: Center ZDV
Aircraft component: FMS/FMC
Component problem: Design
Reporter organization: Corporate
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Human factors: Human-Machine Interface; Situational Awareness; Workload
Anomaly: ATC Issue All Types; Aircraft Equipment Problem Less Severe; Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft; Procedure
Primary problem: Ambiguous

Narrative: Initially we had filed and were assigned the DEBERRY2 Arrival in to COS. At some point in the descent into COS; ATC changed us to the OZZZY3. In the descent on the OZZZY3 Arrival into COS; we noticed and discussed that we had been 'kept high' by Denver Center; and were at about FL330 crossing TULLL intersection. Sometime after passing TULLL; estimating around 5-10 NM past TULLL enroute to HYMNS; we were told to 'Descend via the OZZZY3' and repeated this back to ATC. We then; per SOP and Primus Epic instructions/limitations; as well as our training; entered the lowest altitude into the AAD; which was 14;000 feet at OZZZY intersection; and engaged VNAV.It appeared at first to capture and begin the proper descent profile to cross HYMNS at FL230 and so on for the 'descend via' clearance. In the meantime; we entered the RNAV (GPS) Y Runway 17R into the FMS as a backup for our impending visual approach to that runway. When this was activated/entered into the FMS flight plan; something caused the VNAV profile to completely drop out; [resulting in] all of the mandatory altitudes - FL230 at HYMNS; 17;000 feet at HGO; and 14;000 feet at OZZZY - to be replaced by FL230 for all three. This was highly unusual; we had never seen it before; and it caught us off guard completely. It caused the VNAV profile to be incorrect; and the aircraft/autopilot slowed its descent so much that we quickly fell behind the descent profile and saw that we were not going to make the FL230 restriction at HYMNS.We were about 2 miles from HYMNS when we noticed this. I quickly fixed the problem in the FMS/Primus Epic system by reloading the STAR; doing a 'Direct To' 14;000 feet at OZZZY command; and re-engaging VNAV. The system captured and corrected itself; but was at too steep of a profile to meet the FL230 restriction at HYMNS; but appeared that it could make the one at HUGO and subsequent one at OZZZY (17;000 feet and 14;000 feet respectively). About 1 NM from HYMNS and at approximately FL250; I notified Denver Center that we would not be able to make the restriction at HYMNS; to which they replied 'Ok; make the one at HUGO'; which we read back and complied with. We had no further issues.I believe that poor coordination by Denver Center; keeping us high and then expecting us to 'fix' their mistake by issuing a 'Descend Via' clearance late in the game; set us up for failure here.I feel that this is an abuse of the 'Descend Via' clearance; and that ATC should not be able to use this unless an aircraft begins at an optimal altitude and glide path angle (standard 3 degrees) for the typical FMS/VNAV setup to handle correctly. In my opinion; SOP/FARs should dictate that they have to 'manually vector' aircraft to that optimal altitude before issuing the 'Descend Via' clearance; and I really don't understand why this is not a rule; because it's causing daily problems in our ATC system.Also; in my opinion Honeywell has created a poor and unreliable product in the Primus Epic system; and/or [our company] has done a poor job of training pilots for this scenario. I still don't understand why; when I've already entered/captured/and am on a STAR descent profile; why the 'pre-loading' of an approach for backup purposes should EVER override anything on the previous inputs. They should be mutually exclusive and disconnected; unless designed otherwise. Usually when we do this we get what is commonly called a 'good discontinuity' in the FMS; but we didn't this time. It somehow connected the two (presumably because ADANE intersection is both on the OZZZY3 and the RNAV GPS Y 17R); which from a lateral navigation standpoint would have been fine; but it SHOULD NOT have overridden our vertical profile and altitudes from OZZZY intersection backwards. However it did (making them all FL230) for an unknown and I suspect glitch-driven reason.The late descent from ATC; coupled with a 'Descend Via' clearance (which was in our opinion an off loading of responsibility [from] ATC to the flight crew; where we were meant to 'fix' their earlier poor planning and mistakes); and the FMS anomalies; contributed to us missing the crossing restriction at HYMNS.To our knowledge (absence of other aircraft on the TCAS; no RAs; no alerts); there was no conflict that resulted with another aircraft.




Synopsis: CE-680 First Officer reported failing to make a crossing restriction on the OZZZY3 arrival into COS; citing a late ATC clearance and issues with the Primus Epic FMS system as a contributing factor.