A320
Flight Crew Air Transport Pilot (ATP)
Training / Qualification; Human-Machine Interface; Situational Awareness; Confusion
Aircraft Equipment Problem Less Severe; Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance
Chart Or Publication; Human Factors; Weather
Was in contact with Washington Center at FL260 just passed LYH VOR in light to moderate chop; asked for lower altitude and descended to FL240;  had a hard altitude crossing restriction of FL240 at MAYOS in the MCDU on the IVANE5 RNAV STAR into Charlotte.  Next was a frequency change to Atlanta Center and was cleared to descend VIA the IVANE5.  We set altitude alerter to 6000 feet for the bottom restriction on the IVAN5 STAR.  The FMS decided to drop the flight restriction of FL240 at MAYOS fix all by itself.  The aircraft began to descend to FL220 looking at the next restriction of KIYEN. Next call was from Atlanta Center asking what altitude are you descending to? We were just passing 23;500 feet. It was too late to intervene and make the FL240 restriction at MAYOS. We were instructed to descend to FL220 by Atlanta Center and missed the restriction of FL240.  We asked ATC if there was a conflict with traffic and none was noted at this time. There is a corridor that has passing traffic below FL240 at MAYOS.    We were relying on automation of the FMC and high workload due to turbulence on the descent phase of flight.Double check FMS and intervene at all fixes with a hard altitude at the beginning of the STAR.  Never trust the FMS 100%
We did not notice that the Mayos restriction of FL 240 had been deleted from the computer due to the early descent.
After descending to FL240 due to turbulence the flight crew of an A320 was cleared to descend via the IVANE RNAV STAR to CLT. Although they had set FL240 as a firm crossing on their preplanned programming of the arrival they failed to realize that so doing satisfied the crossing restriction at MAYOS (Between FL260 & FL240) and; thus; the restriction was removed from consideration by the FMGC. When they selected a VNAV/Managed Descent the FMGC factored the next crossing at KIYEN (At or above FL220) and began a descent...thus triggering the deviation. The Primary reporter cited reliance on automation as a contributing factor.