Training / Qualification
ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification
Airspace Structure; Chart Or Publication; Procedure
Enroute to BWI we were cleared for the RAVNN6 arrival via the BKW transition. As we started our descent on the arrival; ATC asked us which part of the regulations we were operating under. I told her we were operating as a part 135 flight; and she said 'ok' then handed us off to the next controller. Before I accepted the hand-off; I asked why she needed to know which part we were operating under. She said it had to do with the airspace around Washington D.C. but that we were fine and there was no issue. I accepted the hand-off and we continued the arrival and landed without incident. After ATC had asked us the question about our operations; however; we took a closer look at the STAR on the iPad. We found a small note at the top saying that part 91; part 135 and several other operation types were not allowed to shoot the RAVNN6 arrival via certain transitions; including BKW; which is the transition we were assigned.  The note for this arrival was in fine print at the top of the STAR diagram. If it was in bold print we probably would have noticed it and requested a different transition on the arrival.
Arrival procedures within the DC area and into BWI are restricted to limited types of operating regulations. ATC cleared flight for the RAVNN6 STAR BKW transition into BWI normally prohibited to part 135 operators.