Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 188; Flight Crew Total 17335; Flight Crew Type 529
Workload; Troubleshooting; Confusion
Aircraft Equipment Problem Less Severe; Deviation - Altitude Overshoot; Deviation - Altitude Crossing Restriction Not Met; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Flight Crew Overcame Equipment Problem
Aircraft
Descending via STAR ZZZZZX to ZZZZ; VMC conditions; FCU set to SEL SPD 250 kts; NAV; DES; confirmed by FMA's. Just prior to fix ZZZZZ1 approximately 10;000 feet; both Captain and First Officer ND displays went blank for a few seconds. When displays came back on; it took a few seconds for the map functions to return and for us to figure out that the FCU had reverted out of NAV into HDG mode. I manually placed us on a corrective HDG and rearmed NAV mode which then engaged and started to track correctly to the RNAV course. We then started cross checking and observed that not only had the NAV mode reverted; but the descent mode had reverted out of managed descent with constraint protections into Vertical Speed mode; 1800 FPM descending. We caught this at approximately 8;000 feet; shortly after passing fix ZZZZZ1; which has a crossing constraint of 9;000 feet. I disengaged the AP; hand flew and started a level off correction. The next fix was ZZZZZ2 with a constraint of 7;000 feet. We manually set 7;000 feet in the FCU; and set the remaining STAR and APP fixes crossing altitudes and air speeds manually. I hand flew the remainder of the STAR and LNAV App RWY XX in VMC conditions to an uneventful landing.
A319 flight crew had both navigation displays fail on the arrival. The flight crew manually flew the arrival and landed without incident.