SAN MATEO, CA, USA
N39658
PIPER PA-32RT-300T
THE AIRCRAFT LOST ENGINE POWER AFTER TAKEOFF AND WAS FORCED TO LAND ON A RESIDENTIAL STREET. THE ENGINE HAD BEEN OVERHAULED BY AN FAA-CERTIFIED REPAIR STATION 5 MONTHS AND 150 FLIGHT HOURS BEFORE THE ACCIDENT. EXAMINATION OF THE ENGINE MAGNETO REVEALED INTERNAL CORROSION AND ELECTRICAL ARCING AT THE BREAKER POINTS. THE INSULATION ON THE 'P' LEAD WIRE WAS CRACKED ALONG ITS ENTIRE LENGTH EXPOSING BARE WIRE AT ONE POINT. GROUNDING OF THE 'P' LEAD AS A RESULT OF A BARE WIRE TOUCHING THE AIRFRAME WOULD HAVE THE SAME EFFECT AS THE IGNITION SWITCH IN THE OFF POSITION.
On September 25, 1994, at 1350 hours Pacific daylight time, a Piper PA-32RT-300T, N39658, lost engine power after takeoff and was forced to land on a residential street in San Mateo, California. The airplane was being operated by Aero Haven, Inc., Big Bear City, California, as a personal flight. The airplane was destroyed. The certificated private pilot and passenger received serious injuries. The flight originated from the San Carlos Airport, San Carlos, California, about 1345 hours and was destined for Big Bear City. Visual meteorological conditions prevailed. The pilot stated the engine quit abruptly 1,000 to 1,500 feet above the ground over a city. The pilot manipulated the throttle in order to regain power. After getting no response, he elected to land on a residential street. The airplane struck wires during the initial flare and then struck an automobile and finally a brick wall during the ground run. The airplane's maintenance records revealed the engine had been overhauled by a Federal Aviation Administration (FAA) certified repair station on May 5, 1994, about 150 flight hours before the accident. The repair station certified the airplane to be airworthy after the engine was reinstalled and returned the airplane to service. The airplane's engine was examined at the El Monte Airport, El Monte, California, on October 21, 1994. Examination of the magneto revealed internal corrosion and electrical arcing at the breaker points. The impulse coupling was found intact and functioned. The insulation on the "P" lead wire was cracked along its entire length exposing bare wire at one point. According to the engine manufacturer, the "P" lead wire connects the magneto's coil with the ignition switch. With the ignition switch in the off position, the "P" lead grounds the primary current. With the "P" lead grounded, the opening of the breaker points does not interrupt the primary current, preventing any build up of voltage in the primary circuit. Without primary voltage, the magneto will not fire the spark plugs. Grounding of the "P" lead as a result of a bare wire touching the airframe would have the same effect as the ignition switch in the off position.
A deteriorated magneto grounding ('P' lead) and failure of maintenance personnel to detect this condition when the engine was reinstalled in the airframe after overhaul. The lack of suitable terrain for the forced landing was a factor.
Source: NTSB Aviation Accident Database
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