N773GB

On December 31, 2023, about 1315 central standard time, a Cirrus SR22T, N773GB, sustained substantial damage when it was involved in an accident near Davenport, Iowa. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot reported that, as the airplane descended to land at Davenport Municipal Airport (DVN), Davenport, Iowa, the engine began to run rough. He noticed that the No. 5 cylinder was cooler than the other cylinders, and the oil pressure was dropping. An “abrupt engine noise/loss occurred,” smoke came from the engine cowling, and oil splattered over the windscreen. The engine lost total power and the pilot executed a forced landing to a corn field. During the forced landing the airplane’s landing gear collapsed and both wings sustained substantial damage.

Postaccident examination of the engine revealed that the No. 5 cylinder had fractured in the area near the exhaust rocker arm, which resulted in separation of a portion of the cylinder head casting and rocker arm assembly. The remainder of the engine exhibited failures consistent with lack of lubrication, including failure of the Nos. 3 and 4 cylinder connecting rods.

The airplane was powered by a Continental Aerospace Technologies (CAT) model TSI0550K1B engine. The broken cylinder head, part number 658595, was subject to AD 2020-16-11, which required compliance with CAT MSB18-08. Review of maintenance records showed that the broken cylinder had been removed, repaired, and reinstalled on the engine on February 26, 2021. At that time, MSB18-08 revision B was the current version of the service bulletin. The repair work was performed by a certified repair station and noted compliance with AD 2020-16-11. The other five cylinders that were installed on the airplane were not subject to the AD. The MSB required covered cylinders to be inspected and modified to remove casting flash build-up or a sharp radius edge condition.

The broken cylinder from the accident airplane, along with two cylinders from other airplanes that had fractured in a similar fashion, were examined by the NTSB Materials Laboratory. Each of the three cylinders exhibited evidence of attempts to comply with the MSB. The examination of the cylinder from the accident airplane revealed that the area identified for blending in the MSB had features consistent with material removal and blending of the edge at the location specified for inspection and modification in the MSB. The blended region extended approximately 0.15 inches underneath the ear and 0.12 inches deep into the cylinder head rocker box footing. The MSB stated that the blended area should extend approximately 0.25 inches underneath the ear.

Examination of the outer edge of the second cylinder revealed material removal and blending along part of the edge. The blending did not extend up to the internal edge on the underside of the ear. Instead, a sharp outer edge was observed extending approximately 0.06 inches from the corner.

Examination of the third cylinder revealed rounding of the outer edge, consistent with filing of the edge as described in the MSB. At its greatest extent, the blending extended approximately 0.24 inches underneath the ear and 0.10 inches deep into the footing. On this cylinder, there was a fracture, but the rocker box ear had not fully separated.

All three examined cylinders exhibited fracture surface features consistent with high-cycle fatigue, with fatigue origins in the area noted in MSB18-08 for blending.