Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical
Air Traffic Control Provided Assistance; Flight Crew Landed in Emergency Condition; General Declared Emergency
Aircraft
Upon receiving the aircraft; there was an open write-up for the left main gear not showing in the down and locked position. Maintenance had not been to the aircraft yet. We called Maintenance and asked if it was okay to power up the aircraft. Upon powering up the aircraft; the gear was showing down and locked. On the walk-around I noticed that the proximity sensors had a lot of dirt on them. Maintenance cleaned the sensors on all the gear and we left on schedule.It was a routine flight until the gear was extended for landing. The left main landing gear was not showing down and locked and we received an EICAS message for the misconfiguration. We aborted the landing; but continued to fly over the runway to have the Tower take a look at the gear. The Controller told us that the gear 'looked different and did not appear down.' We performed a go-around and started the QRH items once we leveled off. The Flight Attendant was also notified at this time. We followed the QRH; and were unsuccessful at getting the left main gear to show down and locked using the normal; electrical override; and free-fall methods. We also tried to side slip the aircraft. We did one additional low approach to have the Tower and emergency personnel take a look; but they could not verify if the gear was down. An emergency was declared and we requested Crash/Fire/Rescue services. The Flight Attendant prepared the cabin for a possible emergency evacuation on the runway with the idea that the left main gear may collapse. We verified the QRH was complete; confirmed the cabin was prepped; and briefed our intentions for both an uneventful landing; and landing with the gear collapse. We landed without incident; and came to a stop on the runway. Maintenance was there and pinned the left main gear and confirmed that it was locked. We then taxied to the gate under our own power.Once parked at the gate; Maintenance looked at the gear proximity sensor and the Mechanic said the gap looked too large and would cause it to give a not down and locked indication. He was able to close the gap a small amount by pushing on the sensor with his hand; and that gave the gear a 'down and locked' indication. When he released his hand from the sensor it returned to the red box with diagonal stripes.
ERJ-145 crew received an unsafe gear indication during landing.