NTSB Identification: ERA11LA502
14 CFR Part 91: General Aviation
Accident occurred Friday, September 23, 2011 in South Deerfield, MA
Probable Cause Approval Date: 04/10/2013
Aircraft: CESSNA P210N, registration: N210LE
Injuries: 2 Serious.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

According to the pilot, during the initial climb, the airplane experienced a loss of electrical power. The pilot said that he unsuccessfully attempted to restart the alternators by cycling the on/off switches. The airplane was in instrument meteorological conditions, and when he saw a clearing in the clouds, the pilot made a “standard rate” spiral down through it. After exiting the clouds, he found a suitable place to land. On the approach, about 300 feet above ground level, the airplane started to porpoise. The pilot attempted to correct the porpoise, but the nose of the airplane struck the top of a tree before impacting the ground.

Postaccident examination of the airplane’s flight controls did not reveal any mechanical anomalies. The engine examination revealed that incorrect pistons were installed at the time the engine was overhauled about 350 hours before the accident, but this did not play a role in the accident. The airplane was equipped with a dual alternator system. A postaccident interview with the pilot revealed that he attempted to energize the alternator’s field utilizing the pilot operating handbook procedure for a single alternator system. The dual alternator system emergency procedure was a supplement for the pilot operating handbook, and the checklist that was located in the airplane did not contain the normal or emergency procedures that were required for the dual alternator system. The emergency procedure for the dual system stated to depress the ALT RESTART switch, located next to the circuit breaker panel; the pilot stated that he did not know about the ALT RESTART switch. The No. 1 alternator was tested and examined. The No. 1 alternator functioned for 5 minutes during the test before it stopped producing power. It showed signs of excessive heat consistent with overloading when examined internally. The No. 2 alternator was not tested due to accident damage. The internal examination revealed burnt windings.

The onboard engine data monitoring system indicated that the battery voltage decreased rapidly just prior to the loss of electrical power. A postaccident examination of the airplane’s electrical system revealed that the alternator restart battery pack did not contain enough voltage to reenergize the alternator field in the event that an alternator failed. A functional test of the system was required every 25 hours to ensure it worked correctly. The batteries were required as per the Airplane Service Manual to be replaced annually or sooner if the alternators cannot be restarted under a heavy load electrical load. A review of the airplane’s maintenance records revealed that most recent documentation for the alternator restart system batteries change was about 12 years ago.

It is likely that the No. 2 alternator failed at an unknown time, which resulted in the entire electrical system on the airplane feeding off of the No. 1 alternator. The No. 1 alternator subsequently overloaded and failed, and the airplane’s battery was unable to sustain the electrical system demand. If the BEFORE TAKEOFF checklist for a dual alternator equipped airplane had been completed, the pilot could have detected that the airplane’s electrical charging system was not working correctly.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The failure of the electrical system due to an alternator failure during flight in instrument meteorological conditions, and the pilot’s inadequate preflight inspection and failure to use the approved checklist for the dual alternator system. Contributing to the accident was the inadequate maintenance because the alternator restart battery pack was not replaced annually, as required by the airplane service manual.

Full narrative available

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