Date: 201712
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 5
Light: Night
Aircraft: Dash 8-400
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Landing
Airspace: Class E ZZZ
ATC / advisory: CTAF ZZZ
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Confusion
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Ground Event / Encounter Other / Unknown; Ground Incursion Taxiway
Detector: Person Flight Crew
When detected: Other landing
Result: Flight Crew Became Reoriented
Contributing factors: Airport
Primary problem: Airport

Narrative: About 3 miles or more out I called the runway in sight and landing. As we proceeded inbound; I felt like there wasn't enough lights on. I clicked the mic switch 7 times to make sure the lights were on. I didn't see much if anything change. I was looking through the HUD at the time and I moved my head to the side to see if maybe the HUD was somehow obscuring my view of the lights. I didn't see anything different so I thought I must just not be seeing absolutely everything but believed it would be more clearly seen as we got closer. As we proceeded; in the back of my mind; I felt that I should be seeing more lighting and I tried once maybe two times more with the mic switch to see if either I had inadvertently turned the lights down low or what was going on. At the same time I am seeing the PAPI and also the blue lights of the taxiway (as I am writing this it seems clear what I was seeing but at the moment it did not). And I am thinking I should be seeing more lights. As we came  closer to what I thought was the runway; I started to pick up more of the pavement to our  left than in front of us where we were lined up to land. This is happening very fast obviously and we are getting closer to where the runway should be but I am not seeing it where I think I should be. I am seeing pavement to our left and in the last moments my mind says - there is pavement over there and lights on either side; go land there because you don't want to land in the dirt and you must have mistaken what you thought was where the runway was going to be for nothing and you had lined up to the right of the runway so slide a little left and land on the runway (again this is what my mind is thinking). And yes the 'runway' seemed a little smaller but this is ZZZ and it will seem smaller based on the width of the runway. Either just as the main landing gear was touching the pavement or just prior my FO said 'this is the taxiway' and by that time the plane was on the ground and it made more sense to slow the plane down and assess what just happened then try to go around. We then taxied to the end of taxiway and turned on the runway. There was no other way to turn around to go to the ramp area other than this. So we proceeded on the runway and exited; then proceeded to the ramp where we parked and nothing more took place as far as the flight. No pax were injured; the crew was fine and the plane was fine. We just landed on the taxiway instead of the runway. As we were taxiing on the runway; I was trying to figure out what happened with the lights for the runway. I clicked the mic button trying to get the lights to turn on but they would not. I finally saw some of the landing light posts where the lights should be lit up and they were dark. After parking the plane I went outside to see if others had seen the lights come on or if anyone notice the lights weren't on or just what was going on. Others (rampers) didn't see the lights on the runway but I have no idea when they made this observation. Nothing further happened with the flight.


Second narrative: I was a required crew member on a flight that inadvertently landed on taxiway instead of [the runway]. I was acting as pilot monitoring and first officer during the flight.During an otherwise normal approach both the captain and I called runway in sight right inside of the (FAP) when we both believed that we had the runway in sight. It was not until touch down was imminent; we observed that in fact we were on a taxiway. It was later determined that at some point during our approach the runway lights had shorted out; but the taxiway light remained illuminated.After landing we noted we were on a taxiway and continued until the end and back taxied down the runway to the gate.The mist and the failure of the runway lights definitely are contributing factors the this inadvertent landing. Up until the point of touchdown; my opinion is that both the captain and I felt that we had the runway environment in sight.


Synopsis: De Havilland DH8D flight crew reported an inadvertent landing on a taxiway instead of the runway.