Accident Details
The aircraft was on its takeoff roll when the left main landing gear and nose gear retracted. The event occurred during a flight that was the first after a modification to the aircraft's Hobbs meter switch.
Investigation Findings
Examination revealed that a flight switch for the Hobbs meter had been installed to automatically record flight time only when the switch was in the 'flight' position. In this position, the Hobbs meter was tied to the weight-on-wheels system. The switch had recently been modified, and the accident flight was the first with the switch set to the flight position.
Testing
A post-accident test demonstrated that with the switch in the flight position, the landing gear retracted even when the gear handle was in the down position. No test of the landing gear had been performed after the modification and prior to the aircraft being released for flight.
The findings highlight that the gear retraction occurred due to the interaction between the modified Hobbs meter switch and the weight-on-wheels system, which bypassed the normal gear handle control.