Cardinal 177/177RG
Flight Crew Instrument; Flight Crew Private
Flight Crew Last 90 Days 4; Flight Crew Total 1105; Flight Crew Type 650
Situational Awareness
Airspace Violation All Types; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Human Factors
I had just made contact with Potomac Approach for entry into the Washington DC SFRA and landing at Manassas (HEF). I was beneath the outer ring of Dulles (IAD) Class B approximately 16 mi west of IAD and flying east; when Potomac requested 'say intentions.' Not taking the hint; I thought they were asking why I was approaching HEF from the northwest when traffic was landing to the north. I responded with my intent to enter downwind traffic at Manassas. 15 miles west of IAD; was informed by Potomac that I had entered Class B (where the floor lowered to 2500 MSL). I was between 2500-3000 at the time. I descended quickly below the Class B floor and leveled off at approximately 2000 MSL as I adjusted course to pass through a gap in an approaching ridgelined. 12 miles [from] IAD; Potomac again called told me that I had entered IAD Class B; that the floor was 1500 MSL; and asked me to turn to the south. At this point continued to descend cautiously as I was less than 100 ft. above nearby obstacles along the ridgeline. I was unable to turn south immediately because this would have taken be across a higher part of the ridgeline again. Once I gained lateral separation from the ridgeline; I turned to the south as I continued to descend to approximately 1400 MSL as I continued toward Manassas. Although I am familiar with this part of the Washington DC area; and was aware of this particular area where the terrain nearly reaches the floor of the IAD Class B; it was not entirely apparent to me that this was where I was flying and that I was approaching this trap.
C177 pilot reported ATC advised him of Class B violations.