Date: 201712
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Dawn
Aircraft: Regional Jet 700 ER/LR (CRJ700)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Security
Detector: Person Flight Crew
When detected: Pre-flight
Result: Aircraft Aircraft Damaged; Flight Crew Overcame Equipment Problem; General Flight Cancelled / Delayed; General Maintenance Action; General Police / Security Involved
Contributing factors: Company Policy; Human Factors; Procedure
Primary problem: Human Factors

Narrative: Upon preflight inspection; the Avionics Bay Door was found open; according to an EICAS message. I put it in the log and called dispatch who transferred me to maintenance. Maintenance Control confirmed that no maintenance was performed on the aircraft the night previous and there was no reason this door should have been opened and that this was a security issue. While waiting for station mechanic I inspected the door myself and found the Avionics Bay Door to be wide open with the light off. They sent out a mechanic who inspected the area and secured the door; however; they reported to me that they found the light on and the door wide open and off the track when they arrived. Due to the security of the aircraft being compromised; I talked to dispatch and we agreed to have the ground crew conduct a new full aircraft search.After I verified that the door was; in fact; open; not just a sensor issue; I spoke with two ramp agents who were loading bags into the forward cargo. They told me that years ago they would regularly open the Avionics Bay Door to 'depressurize the aircraft' in order to open the Main Cabin Door; but that they no longer do this. I explained to him that the aircraft does not pressurize in this configuration and that the Main Cabin Door has a vent to release pressure. I asked him if he knew if any of the ramp crew opened the door and he said no. The ramp manager also spoke with me and told me this was their procedure years ago but they did not do it anymore. He could not explain why this door was opened in the first place. If the ramp crew did open the door to 'vent' the aircraft then they have a poor understanding of how to open and close the aircraft doors as well as poor procedures and this needs to be addressed. [No one] in ZZZ could not explain to me why the compartment was accessed at this time. The ramp manager told me they could not do a full aircraft search because they did not have the manpower. As safety and security is a priority; I told him that regardless it needs to be done. This way of thinking is bothersome; his way of thinking appeared to be that security only matters if they have enough staff. The station manager; however; was on board that safety and security needed to be made a priority. The mechanic in ZZZ was concerned with the door being opened and the ramp manager's careless attitude and they informed the Port Authority Police. The police only asked for my name; title; airline; and telephone number for the airline. A full aircraft search was conducted and we operated uneventfully to our destination. The ramp crew should be re-educated on how to properly secure an aircraft and how to properly open the Main Cabin Door. Everyone should be vigilant for security issues.




Synopsis: CRJ-700 Captain reported a security concern when the avionics bay door was found to be open during preflight.