Date: 201901
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: IMC
Aircraft: B757 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class B ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Hydraulic System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Human factors: Troubleshooting
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed in Emergency Condition; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: I was the Captain on Flight XXX to ZZZ. Flight was uneventful until final approach into ZZZ. During the ILS approach to [Runway] ZZC; as we lowered the landing gear; we heard what sounded like two small explosion/bangs in the back of the aircraft. The first EICAS message we noticed was a GEAR DISAGREE. The right main gear and the nose gear showed green down and locked while the left main gear did not. We coordinated with ZZZ Approach Control and went around from the approach. Shortly thereafter; the EICAS L HYD QTY light came on and we verified a loss of all left hydraulic quantity and then a L HYD Pressure EICAS appeared. I was flying the aircraft. There was a considerable amount of vibration so I elected to keep flying the aircraft while the First Officer started running the checklist for the unsafe gear indication to include an alternate gear extension followed by the hydraulic quantity and pressure indications. We quickly talked to the flight attendants and gave them the info in the TEST communication procedures. I told them to prep for evacuation as I did not know the status of the left main landing gear combined with the vibration and very loud explosive noise during the gear extension. A short message was sent to Dispatch and we requested Tower to notify the Company. ZZZ Tower asked if we wanted to flyby down the runway to see if either they or another aircraft on the ground could see if the left gear was extended or not. I gave an initial PA to the passengers and told them we were working on an issue and going to do an approach by the runway to allow the Tower and other aircraft to tell us what they see. We accomplished that and the aircraft on the ground said it appeared that the gear was extended. We did not change our configuration at all during the go-around or subsequent approaches. (Gear down and flaps 20). One of the checklists (Gear Disagree) said to land with flaps 30 and the other L HYD said flaps 20. We stayed at flaps 20. Landing distance was not an issue. After the second go-around we asked for a short approach as fuel was becoming a concern. We talked to the flight attendants again and told them we were going in for our approach and landing. I made one more PA to the passengers. The Tower had the fire trucks in place. The left main landing gear down and locked green light remained off throughout the landing. We landed on [Runway] XXC and stopped straight ahead on the runway. We kept the passengers in their seats. The landing and rollout was fairly smooth which made me think the tires blew well before landing. Two of the four main tires on the left truck were blown with the other two intact. The Fire Department contacted us directly on the radio. They remarked that there was significant amount of hydraulic fluid near the left gear. Once they cleared the airplane; Operations sent buses to the aircraft and the passengers disembarked. All passengers were fine with no injuries to passengers or crew.Initial inspection by Maintenance stated that a hydraulic actuator piston failed under pressure and may have sent metal into two of the tires as they were leaving the wheel well creating the two loud bangs.The entire crew attended the flight attendants debriefing in the inflight conference room at ZZZ. The flight attendants did an outstanding job throughout. Their professionalism was apparent throughout the event and greatly helped the passengers to remain calm and attentive.


Second narrative: [Report narrative contained no additional information.]


Synopsis: B757 flight crew reported a loud bang and an unsafe gear indication on approach.