EMB-120 Captain reported the left main landing gear would not retract after takeoff; and was accompanied by severe vibration at the nose section of the aircraft. The flight crew performed an air turnback and found a Mechanic who confirmed that the latch under the left main gear door was loose; and popped it in. After taking off for a second time the gear issue remained; and the flight crew proceeded to perform another air turnback and grounded the aircraft for maintenance upon landing.

Narrative

Took off from ZZZ. Left main gear did not retract and nose section had severe vibration. Immediately decided to return to ZZZ. Upon parking the plane my FO (First Officer) and I realized a latch under the left main gear door was loose. We briefed a Mechanic; who was on the ramp; of the situation and they concurred that the latch was the culprit. They popped it in and we took off again. The gear issue remained; so we had to do another return to ZZZ. At this point; I decided the issue was maintenance-related and elected to write it up and down the plane. I contacted our Maintenance Control and followed proper procedures for writing up the maintenance issues. Then; I filed a company hazard report for the air returns; as is company procedure. I realize now after talking with my Chief Pilot that I should have written the aircraft up before taking off the second time. At the time; I did not think about 14 CFR Part 135.65. I should have consulted my Maintenance Control department and followed proper procedure after the first air return.