Pilot Debrief

CONSOLIDATED AERONAUTICS INC LAKE MODEL 250 near Middle Grove, NY — 2013-08-27

Final reportERA13LA382
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Date
2013-08-27
Location
Middle Grove, NY, USA
Aircraft
CONSOLIDATED AERONAUTICS INC LAKE MODEL 250
Registration
N522WB
Category
Airplane
Highest injury
Minor
Fatalities
0
Phase of flight
Climb

Probable cause

Maintenance personnel’s application of insufficient torque to the No. 6 cylinder connecting rod bolts during overhaul, which resulted in the fatigue fracture of the connecting rod and a subsequent total loss of engine power.

NTSB narrative

The pilot stated that, shortly after takeoff, the engine experienced uncommanded rpm changes, so he turned the airplane to return to the departure airport. He then heard a "loud bang" and the engine running roughly, and it subsequently lost power. When the pilot realized that he would be unable to land at the airport, he maneuvered the airplane for a gear-up forced landing in a field. With only 1/4 of the length of the field remaining, he intentionally yawed the airplane right to avoid obstructions ahead; the airplane came to rest upright with the engine displaced to the left. Oil was covering the engine pylon, the top portion of the empennage, and the leading edges of the vertical and horizontal stabilizers. Postaccident examination of the engine revealed a hole in the crankcase adjacent to the No. 6 cylinder. The No. 6 cylinder connecting rod was fractured and separated from the crankshaft, and one nut from the No. 6 cylinder connecting rod bolt was not present and was found inside the oil sump. Metallurgical examination of the components of the No. 6 cylinder connecting rod revealed that the connecting rod was fractured through one side of the strap at the crankshaft end of the connecting rod and that the strap segment on the other side of the connecting rod was deformed inward. The fractured strap exhibited fatigue cracks from multiple origins, and the split line face on the deformed segment of the strap exhibited fretting damage. The connecting rod likely fractured due to insufficient clamping force across the split line at the crankshaft end of the connecting rod. Although the No. 6 cylinder had been removed about 110 hours before the accident flight, the work performed at that time was not associated with the No. 6 cylinder connecting rod. Therefore, given that the engine was overhauled only about 153 hours before the accident flight, it is likely that insufficient torque was applied to the connecting rod nut during the overhaul.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Pilot could have aborted the flight after engine issues began.

NTSB coding

Evidence available

  • Photos
  • 17 docket documents
View NTSB final reportView NTSB docket

Docket documents17

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