Date: 201912
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Light: Night
Aircraft: EMB ERJ 145 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
Reporter organization: Air Carrier
Reporter function: First Officer
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Communication Breakdown; Confusion
Second reporter function: Pilot Flying; Captain
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Loss Of Aircraft Control
Contributing factors: Aircraft; Human Factors
Primary problem: Human Factors

Narrative: On arrival at night into ZZZ; aircraft was being marshaled into Gate XXX. Ground crew gave the stop signal for completion of parking; and I distinctly remember watching the Captain set the parking brake which is always what I use as my indication to turn off the fasten seat belt sign and continue with my flow. After completing my flow; I slid my seat back and took off my headset; to which I heard someone scream; 'Woah woah woah!' from outside the aircraft. At this moment I realized the aircraft had begun rolling forward [and] the engines had not been shut off yet. I immediately got on the brakes; which caused an abrupt stop. The Captain also got on the brakes and we both saw; at the same time; the parking brake handle was down and stowed. I distinctly remember watching the Captain pull up and turn the parking brake handle and I never heard the click of the parking brake being released. The aircraft rolled about 10 feet. before being stopped. No injuries occurred on the ground or in the cabin from the abrupt stop. Engines were shut off and passengers deplaned with no further incidents. The Captain and I discussed it and we both agree that the parking brake was definitely set after stopping and did not hear it being released at any point afterwards. A suggestion for myself would be to not become so complacent on making sure the parking brake is set from just the Captain setting the handle. I can also look outside to verify that the aircraft has stopped moving and that everything is secured; as well as the handle being up with the parking brake light turned on.


Second narrative: Upon arrival into ZZZ; we pulled into Gate XXX and I set the parking brake. The FO (First Officer) verified I set the parking brake and then began his flow; and I continued my flow as well. After a few seconds; maybe 5-10; we heard a shout from the right side of the aircraft and both of us looked over; then looked ahead; and realized the aircraft was moving forward. We both immediately applied pressure to the brakes and the aircraft stopped. The aircraft had moved about 6 to 10 ft. beyond the stop bar. I looked down and noticed that the parking brake was in the released position. I set it again; then verified that upon releasing pressure from the pedals that the aircraft continued to stay in position. We both finished our flows; ran the parking checklist; and then discussed the event.Both of us remembered vividly verifying that the parking brake had been set; and the FO mentioned to me that he would never begin his flow and turn off the fasten seat belt sign until verifying the parking brake had been set. We checked with the Flight Attendant and no issues had occurred in the cabin as a result of the sudden braking. The airplane; although forward of the stop bar; did not come in contact with nor was close to any equipment; vehicle; or building. The jet bridge was able to be pulled into position without having to reposition the airplane.I do not know how the parking brake released; I can only guess that when I set the parking brake I must not have rotated it the full 90 degrees and it slipped back into the released position; though neither the FO nor I heard the brake lever snap back into the released position. That being said; because I immediately began my parking flow after setting the brake; I failed to identify that the position of the brake lever changed and that the aircraft began moving because my attention was focused inside the aircraft.Personally; I will now always be verifying more closely that the parking brake stays put after releasing the pedals and will wait to verify no further aircraft movement with the parking brake set; and give the ground crew time to set the chocks before moving my attention inside to continue my flow. It has been [to] my understanding through my training that it is imperative to finish my parking flow as soon as possible; including turning off the hydraulic pumps and engines as a safety measure to the ground crew. However; in light of the event tonight; it seems to me that the safer course of action to all involved is to pause my flow after setting the brakes and disconnecting steering; that it should be safe for the ground crew to approach the aircraft at that point to set the chocks while I maintain my attention outside. Only after verifying that the chocks are set should I continue my flow and allow my attention to come back to the inside of the aircraft.


Synopsis: EMB-145 flight crew reported an inadvertent release of the parking brake at the gate.