ATL05CA024 · Cessna 172N

During cruise flight, the student pilot detected an odor in the cockpit, then she saw smoke coming from a seam in the top of the instrument panel. The student pilot declared an emergency, proceeded toward the airport, and the smoke continued. She decided to land the airplane in the field. During landing roll, the airplane rolled into a drainage ditch and nosed over. Examination revealed the "audio amp" circuit breaker was found popped. Examination of the wiring behind the instrument panel revealed no visible evidence of burning. The circuit breaker was reset and the electrical master and avionics were turned on, and the ARC MX-300 radio in the Comm 2 position did not function. No smoke was observed and no odor was detected. The radio was removed for examination, and no evidence of burning was observed inside the radio case. A review of the Pilot's Operating Handbook for the Cessna 172N revealed no specific procedures for smoke in the cockpit. In Section 3, "Emergency Procedures, Fires," the handbook states, "The initial indication of an electrical fire is usually the odor of burning insulation. The checklist for this problem should result in elimination of the fire." According to the handbook, the checklist procedures for "Electrical Fire In Flight" are: "(1) Master Switch -- OFF. (2) All Other Switches (except ignition switch) -- OFF. (3) Vents/Cabin Air/Heat -- CLOSED. (4) Fire Extinguisher -- ACTIVATE (if available). If the fire appears out and electrical power is necessary for continuance of flight: (5) Master Switch -- ON. (6) Circuit Breakers -- CHECK for faulty circuit, do not reset. (7) Radio/Electrical Switches -- ON one at a time, with delay after each until short circuit is localized. (8) Vents/Cabin Air/Heat -- OPEN when it is ascertained that fire is completely extinguished."

Verbatim NTSB analysis and probable cause from the NTSB dataset