Cowling would explain radar blip too early in sequence for door. Cowling reflects light. Engine bleed air comes from three and others and goes into forward cargo compartment. Door actuator motor gets signal to open and turns cams which are normally stopped by lock sectors, but worn lock sectors allow cams to turn just a few degrees which allow door to slightly open. Frayed wires in door motor bundle rub against metal fuselage and short connection and turn motor on for a few seconds.
Motor gets signal to turn on from adjacent powerful transmitters in main equipment compartment.
182 had EPR gripe not fixed for fatal flight. EPR gripe but all non cargo door gripes omitted from report. The cam sectors are not completely over center and therefore can be forced open by internal force. The manual locking handle jams and looks locked but isn't. The locking sectors get bent and do not fully engage cam sectors.