A319
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Aircraft; Human Factors
On departure out of Denver on the EEONS5 we were assigned to 'CLIMB VIA' the SID. The initial altitude for the departure was set to 10;000 ft; and when we received the climb via instructions I set FL230 and verified the aircraft was in climb mode so it would make the level-offs during the climb appropriately. With the autopilot on and the aircraft in climb mode; prior to the HIDEF fix; it leveled off at 10;000 ft in ALT CST mode to remain at or below 10000 ft at HIDEF. After making the crossing at HIDEF the aircraft continued its climb to 12;000 to make the crossing of at or BELOW 12;000 ft at SHOBO. When reaching 12;000 ft the aircraft again leveled off in ALT CST mode prior to SHOBO. The next crossing was at or ABOVE 14;000 at LUPTN. We received a frequency change prior to SHOBO. The aircraft started its next climb and I verified on the PFD the climb to altitude was set to FL230; I then looked at the ND and noticed the aircraft was climbing prior to the SHOBO intersection which had the at or BELOW 12;000 FT restriction. We were approximately a mile prior and the aircraft had climbed to 12;700. I had missed seeing that we had not made it to SHOBO yet and I then leveled off the climb using the autopilot and began a descent; at this point it was too late and we crossed SHOBO at 12;580ft. When the First Officer checked on to Denver Center just after SHOBO nothing was mentioned by the air traffic controller and I continued our climb to FL230 and I verified that we made our final restriction on the SID of at or ABOVE 14;000FT at LUPTN.The aircraft was in all of the correct modes but for some reason it began its climb prior to making the restriction at SHOBO. The only reason we could think of was the aircraft thought it would not make its next restriction of LUPTN at or above 14;000ft and initiated its climb early to make the restriction. I have noticed in the past that the aircraft sometimes wants to descend below the crossing restriction on the RNAV arrivals and I have become accustomed to intervening by leveling off with the push to level off mode or selecting the crossing altitude so the aircraft will level off. I had never seen the aircraft climb prior to a restriction in the ALT CST mode. I think this was a perfect example of becoming reliant upon the aircraft to make its restrictions on its own. This has taught me to be more diligent in monitoring the aircraft in all phases of flight.
About 1 mile before SHOBO the aircraft automatically started a climb. Both the Captain and I looked at the SID and then the Captain took over control and leveled off; then proceeded down. In the time it took for us to look at the SID and try to understand why the aircraft automatically changed the constraint the plane climbed 700 feet. The Captain quickly corrected the aircraft and ATC didn't question us. After discussing it we believe the aircraft and constraints were correct but the Airbus automatically disregarded SHOBO constraint to comply with the LUPTN constraint which was at or above 14;000 10.7 miles after SHOBO. We think the aircraft couldn't make LUPTN without disregarding SHOBO so it did that. For the future we need to watch the constraints even more closely as the aircraft might adjust things to make constraints further down the road.
A319 flight crew reported the aircraft climbed prematurely from an altitude constraint on the EEONS5 SID; presumably to assure the next restriction was met.