Incident Details
A flight instructor in a retractable landing gear, multi-engine airplane was conducting aerial survey training for a newly hired pilot. The airplane was slowed to the mission airspeed of 117 knots, which required reduced power and the use of more than 15° of flaps. To ensure clear communication, the instructor pulled the circuit breaker to silence the landing gear warning horn but did not pull the landing gear motor circuit breaker. The pilot receiving instruction was unaware that the instructor had pulled the circuit breaker.
While returning to the departure airport, the landing checklist was completed 15 to 20 miles from the airport. The instructor observed that the pilot was "falling behind on power and descent management" and that the airplane was high and fast for the approach. The instructor advised the pilot to correct but began to assist when it was taking longer than anticipated. As the airplane decelerated into the white airspeed arc, the instructor moved the landing gear selector switch to the down position and added full flaps. Because the flaps were added shortly after the gear selector was moved, the instructor could not discern from flight characteristics that the landing gear had not extended. Neither the instructor nor the pilot observed the absence of a green down-and-locked position light indicator. The airplane landed with the landing gear retracted.
Postaccident Examination
The airplane sustained substantial damage to the fuselage and both engines. After the accident, the director of maintenance reported that the airplane was lifted onto jacks and an emergency gear extension was performed. Subsequently, three electrical landing gear retractions were conducted, and no defects were found.
Additionally, a photo provided by the flight instructor showed that the landing gear warning horn and landing gear motor circuit breakers are located immediately next to each other in the cockpit.
Manufacturer's Note
The airplane manufacturer's pilot operating handbook contains a note in the section titled "Landing Gear Warning Horn" that states: "Do not pull landing gear warning circuit breaker to silence horn as this turns off the landing gear control relay, thus the landing gear cannot be retracted." (Note: The source does not explicitly state whether this note was applicable to the accident airplane or if the instructor was aware of it.)