Date: 201703
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Dawn
Aircraft: EMB ERJ 170/175 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Ferry / Re-Positioning
Flight phase: Parked
ATC / advisory: Ramp ZZZ
Aircraft component: Escape Slide
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Time Pressure; Distraction; Confusion; Communication Breakdown
Second reporter function: First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown
Detector: Person Flight Crew
When detected: Aircraft In Service At Gate
Result: Aircraft Aircraft Damaged; General Maintenance Action
Contributing factors: Company Policy; Human Factors; Procedure
Primary problem: Procedure

Narrative: We got to do a ferry flight. After stowing our bags; the FO did a walk around; we both did a check of the interior to ensure the carts/lavs were secure; did our preflight flows; ensured our ferry permit was correct; then we thought we were ready to go. I walked into the jetway and told the gate agent and supervisor we were ready to close and have the jetway pulled.  The agent and supervisor were the only 2 people the FO or I had seen in the jetway or on the plane.  I closed and armed the main cabin door. I then went back into the cockpit to get ready to fly.  After about a minute we heard a strange sound coming from the main cabin door and went back to take a look.  A ramper; which I had not seen before; had attempted to open the 1L door.  The ramper; agent; and supervisor were all standing in the jetway.  The door was approximately 1/4-1/3 open with the slide beginning to deploy; but not yet inflated. We told them to stand back because there was a chance of the slide deploying into the jetway.  We notified ops and called dispatch and maintenance control.Just before leaving a manager came to tell us the rampers side of the story. According to him; the ramper had come on the plane and was still on the plane when we closed the main cabin door.  He then realized the plane was being closed up and needed to get off; so he walked from wherever he had been hiding and opened the 1L door which I had armed.  According to the manager; this long time employee has a history of some non-compliant behavior and seems to be where he has no business being; on a regular basis.Shortly after the door was opened; the first time I saw the ramper; was in the jetway messing with the door and had no reason to expect that he was ever on the airplane at any time. If he was; the cockpit door was open the entire time; and he never stopped to talk to us; or question if it was safe to open the door.  Regardless of if he opened the door from the inside or outside; he had no authority to do so.On a ferry flight; the rampers should have no authority to be anywhere other than the front galley in direct communication with the pilots.On a ferry flight; doing one final check to ensure the pilots are indeed the only ones on the airplane prior to closing the main cabin door.


Second narrative: [Report narrative contained no additional information.]


Synopsis: An ERJ-175 crew preparing to ferry an aircraft described their confusing interaction with the ground crew while preparing for departure. When finally ready; the main cabin door was closed and the slide armed. Unfortunately; an agent had remained in aircraft and activated the slide while attempting to sneak out.