Cirrus Design Corp SR22 N223SS accident near Tappahannock, Virginia

Probable cause

A failure of the engine crankshaft top rear trailing forward counterweight retaining plate, which resulted in a total loss of engine power. The reason for the retaining plate’s failure could not be determined during postaccident examination.

NTSB analysis

The pilot reported that the airplane was in cruise flight when he heard a "loud noise" come from the engine, followed by a loss of engine power. The pilot established the airplane's best glide speed and declared an emergency with air traffic control, and an air traffic controller then provided vectors toward the nearest airport. While approaching the airport, the pilot heard another loud noise come from the engine, and oil then covered the windscreen. The pilot chose to deploy the airplane's parachute system, and the airplane descended under the canopy until it came to rest among trees.

Examination of the engine revealed that the crankshaft top rear trailing forward counterweight retaining plate was fractured; the counterweight pin and portions of the plate were found in the crankcase and oil sump. The No. 2 connecting rod was fractured, and the crankcase exhibited significant damage concentrated at the No. 2 cylinder. A material analysis of the fractured counterweight pin revealed failure signatures consistent with overload. The hardness of the plate met manufacturer specifications, and microstructure analysis of the plate appeared normal.

About 4 years before the accident, the engine manufacturer issued a critical service bulletin (SB) "to inform operators of the possible long term effects of low engine RPM in cruise conditions." Models affected included the accident engine make and model. The SB described two instances of sudden engine stoppage as a result of a crankshaft counterweight release. These instances were found to have been associated with engine operation at a sustained cruise rpm of less than 2,300 rpm. As a result, the manufacturer recommended that engine cruise rpm settings be no lower than 2,300 rpm. Although the engine operating manual cautioned that the minimum cruise rpm setting was 2,300 rpm, the airplane manufacturer did not include this information in the Pilot's Operating Handbook. A review of recorded data from the accident airplane revealed that nine flights were flown in the 6 months before the accident and that, during these flights, the accident airplane was operated at or below 2,300 rpm for 20 minutes or longer. However, the investigation could not determine if the top rear trailing forward counterweight retaining plate failed due to these operations.

Text from the NTSB. Open the NTSB docket for ERA13LA328 for the full record.