Air carrier flight crew reported a low altitude alert from ATC and CFTT event; and cited distraction and incorrect mode and altitude entry in FMC as contributing.
Synopsis
Air carrier flight crew reported a low altitude alert from ATC and CFTT event; and cited distraction and incorrect mode and altitude entry in FMC as contributing.
Narrative
To the best of my recollection. We were cleared for a visual approach XXR (backup by the ILS). The first officer had left; I believe; 3000 ft on the FCU (Flight Control Unit) and I told him to dial 1800 feet (FAP) altitude for ZZZZZ or we would be high. FO (First Officer) set 1800 and we confirmed the altitude. As we did this; my phone went off (We had a maintenance issue at the gate in ZZZZ and then again as we taxi out. We had to pull to the side while I tried to contact our dispatcher using my phone but could not get a signal. I put my phone down and tried again the iPad to call the dispatcher using the wifi. After conferring with Maintenance Control and having to do a crew placarding; I forgot to turn off my phone). My phone started receiving a bunch of notifications and alerts and it was so distracting that I turn to my left to grab my phone and put it in airplane mode. In just about a few seconds it took to place my phone on airplane mode; the FO for whatever reason; reached up and change the FCU to 5000 feet and pressed VSI. Of course; the plane continue to descend below 1800 feet. As I look up again; I was confused to what I was staring at. I saw that we were descending (already around 1300) and I looked at the moving map trying to figure out where we were and understanding what was going on. I looked at the FCU and saw 5;000 feet which made me even more confused. I said to the FO what the heck what are you doing? All at the same time; ZZZ Control Tower calls out low altitude alert. I told the FO; stop the descend since we were about to capture the LOC and glide slope above us. I just said level off and intercept the glide slope. I figured it out as soon as I saw 5;000 feet on the FCU and VS selected that was the reason for the low altitude alert and why the plane did not stop at 1800 feet as we had done the altitude verification. We were total VMC conditions.FIRST... me getting distracted with my phone going off after forgetting to place it back to airplane mode after having to contact dispatch and Maintenance Control in ZZZZ twice. Once at the gate. Local mechanic came out to do a reset. Then off the gate to do a crew placard for a separate but possible related issue. At the gate was ANTI SKID AND NWS STGRG inop. While taxing; I could not disconnect the rudder pedals to do the flight control check. SECOND.... the FO changing the altitude selected on the FCU and vertical mode and NOT confirming the change while I was distracted. FO set a higher altitude and that is why the plane descended below FAP altitude. Be more proactive to place phone on airplane mode after having to turn it back on off the gate for maintenance issue or having to call dispatch. Also; incorporate to my briefing that any changes to the FCU and/or FMGC need to be verified by both pilots.
Second reporter narrative
Due South of the final approach fix at 2000 feet they cleared us for the Approach. I did set 1800 in altitude selector and started to go down with vertical speed. I was even going to ZZZZZ direct with NAV. On my way down; as I remember; i thought we were low; and i was looking at the glideslope which appeared to be below me. This could have been based on us coming in on an angle. I noticed that the ALT (Altitude) would capture; and while i am thinking we are high; i did spin the ALT selector up so the plane could continue down. At the same time i realize that i was low; the captain noticed as well and the tower asked us. I immediately stopped my descent; disconnected auto pilot; and leveled off. I hand flew the rest of the approach to a full stop landing. The tower vectoring us close to the final approach fix made it tight to be fully established; and if we could have at least been outside the next fix beyond the final approach fix could have helped with trapping errors and given us time to be fully stabilized for the approach. Ultimately; i should have taken a better look to cross reference the glide slope; and i verify what altitude i was at. If they could vector you a little bit further out; especially when they don't have to stress with a lot of people coming in; it might help.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.