Event Summary
The pilot reported entering the traffic pattern to land. Although a printed checklist was on his lap, he did not use it, instead relying on his mental checklist for the landing. The airplane was landed with the landing gear retracted. The pilot was wearing a headset during the landing.
Postaccident System Tests
Postaccident testing of the landing gear extension system revealed no evidence of failure or malfunction. With the airplane on the runway and the master switch turned on, the landing gear 'up' light illuminated. An FAA certificated airframe and powerplant mechanic entered the airplane while it was on the runway, with the master switch on and the throttle at a low power position. The mechanic heard the landing gear warning horn at that time.
However, subsequent postaccident testing of the gear warning system in the presence of an FAA inspector yielded different results. The horn did not operate when the throttle was at a low power setting, the landing gear selector handle was in the 'up' position, and the master switch was turned on.
Pilot Actions
The pilot had a printed checklist on his lap but chose not to use it. He relied on his mental checklist for the landing procedures. No other pilot actions or statements are provided in the source.
Conclusion
The source does not provide a stated probable cause for the accident.