What happened
The pilot entered the traffic pattern to land an unspecified aircraft. Although a printed checklist was available on the pilot's lap, it was not utilized; instead, the pilot relied on a mental checklist for the landing sequence. While wearing a headset, the pilot completed the landing with the landing gear retracted.
The investigation
Postaccident testing of the landing gear extension system showed no evidence of mechanical failure or malfunction. During inspection on the runway, the landing gear 'up' light illuminated when the master switch was turned on.
An FAA certified airframe and powerplant mechanic observed that the landing gear warning horn sounded while the aircraft was on the runway with the master switch on and the throttle at a low power position. However, subsequent testing conducted in the presence of an FAA inspector revealed that the warning horn failed to operate under specific conditions: 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.