Air Carrier flight crew reported ATC told them they took a similar sounding call sign's descent clearance and descended below the minimum altitude for terrain obstruction.
Synopsis
Air Carrier flight crew reported ATC told them they took a similar sounding call sign's descent clearance and descended below the minimum altitude for terrain obstruction.
Narrative
We had been picking our way through thunderstorms and were heading towards ZZZZZ into ZZZ at 12;000 ft. We had been talking with ATC about the deviations for weather and had just let them know we were back towards ZZZZZ. Shortly after this radio call ATC called us and said descend and maintain 10;000 ft. I read this back to them with our call sign. The Captain put 10;000 ft. into the FCU and we started down. When we started down I was thinking we are still a ways from ZZZZZ and we normally cross ZZZZZ at 14;000 ft. We were off our normal course into ZZZ because of the deviations and I thought maybe this is what the controller wanted?As we descended though I thought the terrain looked to close. I was about to key up the mic and ask ATC to confirm the altitude they wanted us to descend too when they called us back and told us we took another aircraft's clearance and we needed to climb back to 12;000 ft. It seemed that this controller was training because another voice came on and asked us if we had been told there was a similar call sign on frequency? We had not been told this we said. The flight continued without incident. Having two flights with similar sounding call signs arriving at the same time into ZZZ is a threat. Hopefully planning can work on changing this.
Second reporter narrative
As we descended into the ZZZ area we responded to an ATC call to descend to and maintain 10000 ft. The First Officer (FO) who was the pilot monitoring read back this clearance with our call sign. I put the altitude in the FCU and we both verified on the FMA. We didn't hear anything else from ATC until we were given a frequency change. We checked into the new frequency with our call sign and descent altitude. As we descend through 11000 ft. I cross referenced my GPWS terrain indication on my ND. The assigned altitude seemed lower than what I remembered in the past and there was some terrain ahead that was now appearing yellow. Our routing was still a few thousand feet above the terrain along our route however and we were VMC so I didn't immediately have concerns and thought ATC had stepped us down a bit early. Descending through 10700 ft. ATC radioed and said to immediately climb to 12000 ft. and that we had taken our company aircraft's descent.Until now we had not been advised of a similar sounding call sign on frequency. ATC now informed us Aircraft Y was also on frequency and in the descent to ZZZ. The flight was completed without incident; but we were informed by ZZZ tower to contact TRACON of a possible pilot deviation. In doing so I had to call back multiple times as they informed me they were unable to access the recordings. Ultimately they called me back and said they were still working out the details but they believed we had taken another aircraft's frequency change but they couldn't say definitively. We never received a similar sounding call sign notification from ATC nor were we corrected during the initial read back or the new frequency check in. Both these things could have trapped this error. In addition having two company flights with similar call signs arriving at the same time should be avoided in the planning phase by the company. While we are not sure if we actually took the other aircraft's altitude assignment or ATC gave the altitude to the wrong similar call sign we admit it was possible that we made an error which we didn't catch.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.