Date: 201509
Local time of day: 1201-1800
Location: ZDV.ARTCC, CO
Flight conditions: VMC
Light: Daylight
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Descent
Airspace: Class A ZDV
ATC / advisory: Center ZDV
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Training / Qualification; Distraction; Confusion; Communication Breakdown
Second reporter function: Pilot Not Flying; Captain
Anomaly: ATC Issue All Types; Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: Beginning the KIPPR THREE arrival into DEN; ATC assigned FL280. Prior to reaching SUSHE; ATC assigned descend via the KIPPR THREE arrival. Pilot Flying (PF) started descent from FL280 prior to passing SUSHE; which had the restriction of FL300 or above. Pilot Monitoring (PM) advised ATC of the descent to which ATC responded 'Roger'. Passing through FL200; ATC inquired as to why the descent was started prior to SUSHE. The PM explained that given our altitude being lower than the restriction at SUSHE; we had interpreted we could begin descending. ATC responded that we were supposed to maintain FL280 until after SUSHE. ATC then handed us off to the next controller; and we continued on the arrival; meeting all altitude and speed restrictions. The flight concluded with no more issues/deviations.There was a misinterpretation of what was expected at SUSHE. Given that the aircraft was assigned FL280; lower than the crossing restriction at SUSHE; the PF interpreted that there was no addition restrictions and began decent to meet the subsequent altitude/speed restrictions. It wasn't until later that ATC explained we needed to maintain FL280 until SUSHE; regardless of the published altitude.The flight crew should spend more time briefing the arrival; which may have allowed us to recognize the unique situation. From there; an inquiry can be made to ATC as to what is expected at SUSHE or other applicable fixes. Another mitigation strategy would be to hold off on descending until passing the first fix with a crossing restriction when given 'descend via' when the aircraft is at a lower altitude; unless confirmed by ATC. In addition; if ATC clears 'Cross SUSHE at FL280; then descend via...' in a similar nonstandard situation; it would have been clear as to what the expectation was for the arrival.


Second narrative: Also; since our altitude as it pertained to the arrival was somewhat nonstandard; a clearance of perhaps; 'cross SUSHE at FL 280; then descend via the KIPPR 3 arrival' would have helped as well.


Synopsis: A flight was cleared to descend and maintain FL280 on the DEN KIPPR 3 STAR; 2;000 feet below the charted SUSHE FL300 constraint. The confused crew continued the descent to cross ANCHR near FL240. ATC queried the crew about the continued descend below FL280 prior to SUSHE.