A C402 Pilot flew with the boarding stairs down because he had no passengers and ramp personnel normally raised the stairs after passenger boarding.

Narrative

I left for my last round trip of the day (I had previously done three round trips earlier in the day). Today was my first day flying on my own in the Cessna 402 as I had just been released from IOE three days earlier; but had been given a couple days off to move to my new base. This flight had no passengers booked and therefore I was instructed to reposition in order to pick up passengers for the return trip. The ramp agents at my departure told me that I could start up and taxi out on my own and therefore I was not given a marshaler. I walked out in the pitch darkness (it was a very dark night) to the airplane and did my normal door check and then security check. I closed the top hatch of the main door as I usually do before starting the security check. I then proceeded to go through my normal flows and checklists (including checking the door annunciator light); taxied out to the runway and departed. Upon my arrival; the ramp agent who marshaled me in came up to the plane and told me that the stairs were down. I realized at that time that it was possible that I had failed to close the bottom hatch of the main door as it was something I did not normally have to do (usually the ramp agent closes the main door for me). I immediately recognized the safety hazard of the situation and began formulating my disclosure for this report. Of course I verified that the door; its latches and lights functioned smoothly and correctly. They were all normal. As it was apparent that the situation arose through my error and that the door did not pop open due to any mechanical deficiency; I did not enter any discrepancy into the aircraft maintenance log. I then proceeded back to my base with passengers without incident. Please be aware that although the submission of this ASAP is outside the normal 24 hour period; I did not have access to the system until late last night. I did; however; notify the Safety Director of my desire to complete a within the 24 hour period. I recognize that I made some serious mistakes that allowed this to happen. First of all; I should have insisted that a marshaler was assigned to marshal me out of the ramp on my solo departure. If I had done so; it is very likely that this situation could have been averted. Also; regardless of whether I have a marshaler or not; I need to visually verify not only that the exterior baggage doors are secured; but also the main door. I should have been especially careful with the main door as the lower section of that door does not have a micro switch to trigger the door warning light on the annunciator panel. This series of mistakes led to a serious situation. I am very humbled by this experience. I want to be a good pilot for this airline and one that goes the extra mile to ensure the safe operation of our airline. I accept complete responsibility for what happened and this experience has reinforced a real sense of appreciation for how absolutely critical it is that I do things correctly each and every time. I recognize that being at the end of a long day; in addition to having a lot on my mind (since it was my first day); led to an unacceptable series of mistakes that led to an unsafe situation. I promise to take my time; do things correctly and always ask for the help I need to make my operations as safe as possible.