EMB ERJ 145 ER/LR
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe
Flight Crew Diverted; Flight Crew FLC complied w / Automation / Advisory
Aircraft
Left main gear would not retract. Selected gear up. After turning we received a red master warning and LG/LEVER DISAGREE EICAS message. We got a heading from ATC and climbed to 5000 to run the QRH. Per QRH we cycled the gear with same disagree indication. As directed by the QRH we lowered gear and [advised ATC] to land at nearest suitable airport. We kept the speed less than 250 and were not in icing conditions. We notified ATC we wanted to head to [a nearby airport]. The captain informed the Flight Attendant and then the passengers of the issue and we descended to 3000 as we approached [the airport]. ATC had us on a right downwind and cleared us for the approach. We declined and asked for more time. We notified dispatch of the situation and ran the arrival checklist. We both also talked about a low pass to see if ATC could give us any information as to if the left main gear was down or damaged or if it even existed. We both knew not to take that information as a guarantee; but instead as a chance to determine if there was an unknown variable in play (for example....damage to our left main gear.) We briefed the approach and talked about our configuration at slow speeds and that we would climb back up to 2000 feet while making right traffic. After the low approach we came back around with right traffic and landed without incident. After exiting the runway; firetrucks approached and inspected the aircraft. They found no visible indication of a problem and we then taxied to the gate. We deplaned and the captain made himself available in the jet way to the passengers in case they had any questions. Contract maintenance was called and they also found no visible problems with the gear. They then pinned the gear in order for it to be ferried. The Captain and I worked as a team to mitigate threats. If I have another emergency in the future I'll try to remember to take my time to read more messages from dispatch. It seemed like it all happened so quickly and it was very busy. ATC was asking us a bunch of questions (fuel on board; nature of [situation]; proceed on course or do we need a heading; what altitude do we want; do we need any assistance; number of souls on board; etc.) all while we're talking to the passengers/flight attendant and running the QRH while maintaining situational awareness of the prohibited airspace and most importantly...flying the plane. I was mainly doing the administrative work while the Captain flew. I asked him for a bit more time to plan the approach and get landing numbers and communicate with dispatch when ATC tried to assign us the visual approach. He thought that was a good idea not to rush and I asked ATC to extend our downwind to get the time I needed to complete those tasks. I received and acknowledged the first few ACARS messages from dispatch but missed the last couple in my haste. If I would have slowed down a bit more I would have seen them before we landed safely.
EMB-145 First Officer reported the left main gear would not retract after takeoff. Crew diverted with a successful landing.