B737-800
Flight Crew Air Transport Pilot (ATP)
Other / Unknown; Human-Machine Interface
Aircraft Equipment Problem Less Severe; Deviation - Altitude Overshoot; Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Aircraft; Human Factors
I was flying the leg to ZZZ. We were given the clearance to descend via the Arrival and I set 10;000 feet in the altitude window. (Not sure what altitude we are at when given the clearance.) I selected the 'alt intervention' button to start the descent. The machine did not respond so I selected the 'alt intervention' button once again; not realizing/recognizing I was in Alt Hold and not VNAV. The effect of selecting alt intervention a second time was to delete the crossing restriction of FL240A (at or above FL 240) at Fix ZZZZZ. The ultimate result was crossing Fix ZZZZZ at approximately FL 230; 1;000 feet below the restriction.I've flown this arrival 100;000;000 times with no deviations; which; of course; counts for diddly squat if your not paying attention that one complacent moment!
A B737-800 Captain upon receiving a descent clearance pushed the alt intervene button which deleted the first crossing restriction and caused the aircraft to cross that fix 1;000 feet low.