What happened
The pilot had recently received training for banner towing operations and was conducting his fifth such flight. After departing from runway 9R, the aircraft turned left, crossing to the left side of runway 9L to establish a left downwind leg. The pilot intended to continue in this left traffic pattern for a banner pickup near the approach end of runway 9L.
While proceeding westbound at an altitude of approximately 100 feet above ground level and a speed of 50 mph, the aircraft reportedly began to settle. The pilot stated that the engine lost power but could not recall events following that point. Witnesses observed the aircraft traveling westbound when it entered a shallow left bank before reversing into a steep right bank. The aircraft then crashed in a steep descent. One witness reported that the aircraft was flying in an unusually nose-high attitude and appeared to stall just before impact.
The investigation
A teardown of the engine revealed that the left magneto intermittently cross-fired. No other pre-accident mechanical problems were identified during the examination.