What happened
During a commercial air taxi flight check being conducted by an FAA inspector, the aircraft experienced a gear-up landing. The incident occurred while the crew was in the traffic pattern and had been engaged in a discussion concerning the procedures for emergency landing gear extension.
The pilot reported that he moved the gear lever to the down position but failed to verify the status of the three green landing gear lights, which confirm the gear is locked down. The FAA inspector also did not recall checking the landing gear indication lights prior to the landing. Neither crew member recalled hearing the gear warning horn or observing the flashing gear-not-extended light located in the landing gear selector handle.
The investigation
Post-accident inspection of the aircraft revealed that the three green gear-locked lights were functioning satisfactorily. However, investigators found that the gear light was operating intermittently. Additionally, it was discovered that the gear warning horn would only sound if the left engine throttle was retarded to the stop with considerable back pressure.