A320
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 89; Flight Crew Total 4693; Flight Crew Type 2898
Troubleshooting
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Provided Assistance; Flight Crew Executed Go Around / Missed Approach; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Overcame Equipment Problem; Flight Crew Landed in Emergency Condition; General Maintenance Action
Aircraft
Aircraft X was uneventful leading up to the approach at ZZZ. We had been cleared for the approach to Runway XX and were established on the localizer and glideslope. The autopilot and autothrust had been disengaged earlier in the approach and the aircraft had been configured to Flaps 3 when Gear Down was requested. When the gear lever was selected down the three indicators on the landing gear panel indicated red UNLK (UNLOCKED); no noise from the landing gear doors opening was heard. Captain [Name] and I communicated and confirmed on the Landing Gear Systems page that the landing gear had not extended. We decided to level out at 6;000 feet MSL while we confirmed the situation and attempted to cycle the gear. We communicated to the tower we would be going around for a landing gear failure approximately 3mi prior to the runway. Tower provided vectors and a climb to 9;000 feet; we initiated a go around over the threshold per ATC instructions and cleaned up the aircraft per SOP. The autoflight was re-engaged after the go around. During this time after the failure of subsequent attempts to cycle the gear and with the lever still down; we eventually got the L/G GEAR NOT DOWNLOCKED ECAM. The ECAM was run according to SOP by Captain [Name] while I flew the aircraft and handled radio calls. We [received priority]; stated our intention to return to land on Runway XYR and requested CFR (Crash Fire Rescue Equipment). Gravity extension was successful and we were vectored to the approach. Approach and landing were normal with the exception of the gear doors remaining open. We landed with 8000 lbs. of fuel. We stopped on the runway and Operations was standing by to tow the aircraft back to the gate.
First Officer reported a Go Around and precautionary  landing after landing gear lock problems.