Single Engine Turboprop Undifferentiated
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Hazardous Material Violation; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Human Factors; Procedure
I met our two passengers at the FBO door. A lineman and I unloaded their vehicle onto a dolly and the lineman pushed the cart out to the aircraft where the First Officer (FO) was waiting to receive the baggage. During the walk out to the aircraft; I noticed that one of the items on the dolly was a locked rifle case. Since we were doing an owner flight in the '135 only' aircraft; this flight would be operated under Part 135 rules; which meant that I needed [Operations] approval to carry firearms. The lineman handed the baggage to the FO for weighing and loading through the cargo door while I called [Ops] for approval (granted) from the cockpit. After landing in ZZZ1; the FO exited the aircraft and took his position outside of the cargo door. Once the passengers departed; I went to the back of the cabin and began offloading their items from the cargo area. While unloading a cardboard box; I could see that one of the items was cylindrical with a bright orange cap (the box top flaps were folded over; but not taped shut). I maneuvered the box to get a better look at the item without opening the box and rummaging through the owner's items. It did appear to be a can of bright orange spray paint. The owner was standing a few feet from the cargo door; so I asked him if the item was a can of spray paint. He affirmed that it was. I politely informed him that for future reference; we cannot transport cans of spray paint since they are considered to be a flammable aerosol and HAZMAT. He said he had not been aware but that it made sense and he apologized for the error. When I had a chance that evening; I emailed [Ops] to discuss the event and plan to complete a DOT incident report for 'undeclared hazardous material found in cargo or baggage.' We currently provide owners with HAZMAT guidance in the Owner Handbook and to charter clients on the Terms and Conditions. However; without actually opening their baggage and inspecting it prior to loading; we cannot fully prevent them from carrying HAZMAT without our knowledge. Had the cardboard box been taped shut; we would not have detected it in this case.
Air taxi Captain reported undeclared HAZMAT inadvertently transported.