PA-23-250 Aztec
Flight Crew Multiengine; Flight Crew Instrument
Flight Crew Last 90 Days 31; Flight Crew Total 2050; Flight Crew Type 1018
Communication Breakdown; Human-Machine Interface; Situational Awareness
Aircraft Equipment Problem Less Severe; Airspace Violation All Types; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Incursion Runway; Ground Incursion Taxiway
Air Traffic Control Provided Assistance; Air Traffic Control Issued New Clearance; Flight Crew Overcame Equipment Problem; Flight Crew Exited Penetrated Airspace; Flight Crew Requested ATC Assistance / Clarification
Aircraft; Human Factors
Was unable to [reach] Ground or Tower. Assumed Tower closed without confirming; departed using CTAF and procedures. Departed runway and pattern and when tuning to Myrtle Beach Approach to activate flight plan I realized the volume knob had been knocked to off position. Activated flight plan and was advised to call Tower upon landing. There are no excuses and I don't know why I jumped to a conclusion without confirming other than that on my last departure at that field the Tower was closed and I departed using CTAF.
PA-27 pilot reported wrongly assuming that Tower was closed; taxiing and taking off without clearance; and using CTAF procedures; all due to the volume knob on the com radio being in the off position.