Small Aircraft
Flight Crew Instrument; Flight Crew Commercial
Flight Crew Last 90 Days 2.3; Flight Crew Total 2378; Flight Crew Type 1498
Communication Breakdown
ATC Issue All Types; Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Clearance; Ground Incursion Taxiway; Ground Incursion Runway
Flight Crew Returned To Clearance
Procedure; Human Factors
During engine run-up at the Runway 24 hold short line and parallel to the runway; an apparently fouled spark plug caused engine roughness on one magneto. I requested a return to the tie-down area; roughly 100 yards behind me on Taxiway Bravo. The Tower Controller responded 'OK' which I interpreted to mean that I could return. I did a U-turn on the taxiway which crossed the hold-short line by roughly 7 or 8 feet; but without any incursion onto the runway. The Controller advised me of a 'possible runway incursion' and then cleared me back to the tie-down area. Despite the fact that I thought the turn would remain clear of the hold-short line; I should have waited for more specific instructions; 'OK' is apparently not a clearance. There was no other departing traffic ahead of or behind me and none landing; so safety was not compromised.
Small Aircraft Pilot reported misunderstanding ATC taxi response resulted in taxiway and runway incursions.