Incident Overview
During cruise flight, a student pilot detected an odor in the cockpit and subsequently observed smoke emanating from a seam in the top of the instrument panel. She declared an emergency and proceeded toward an airport, but the smoke persisted. She then decided to land the airplane in a field. During the landing roll, the airplane rolled into a drainage ditch and nosed over.
Post-Incident Examination
An examination revealed that the "audio amp" circuit breaker was in the popped position. No visible evidence of burning was found on the wiring behind the instrument panel. The circuit breaker was reset, and the electrical master switch and avionics were turned on. The ARC MX-300 radio in the Comm 2 position did not function. No smoke was observed, nor was any odor detected. The radio was removed for examination, and no evidence of burning was found inside the radio case.
Aircraft Handbook Information
A review of the Pilot's Operating Handbook (POH) for the Cessna 172N indicated no specific procedures for smoke in the cockpit. However, Section 3, "Emergency Procedures, Fires," 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." The handbook provides the following checklist for "Electrical Fire In Flight": (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.