Nanchang China CJ-6A N6263D accident near Mesa, Arizona

Probable cause

Separation of the cylinder from the engine during cruise flight due to fatigue in the studs attaching it to the engine casing.

NTSB analysis

The pilot reported that about 30 minutes into the 45 minute-long flight, the engine began vibrating and he maneuvered the airplane back towards the airport. As the airplane joined the downwind leg of the traffic pattern, the pilot heard a "bang," followed by the engine experiencing complete loss of engine power. Unable to land at the airport due to altitude loss, the pilot performed a forced landing in an adjacent park. During the landing sequence the airplane struck a building while the pilot attempted to avoid a pedestrian. The airplane sustained substantial damage to the right wing and forward fuselage. Examination of the radial engine revealed that one of the cylinder heads and its associated piston had become separated. The remaining internal sections of the engine sustained catastrophic damage, consistent with continued rotation after the failure of the cylinder. Half of the studs attaching the failed cylinder to the head exhibited fatigue signatures consistent with insufficient clamping pressure applied to their nuts. A full service history for the engine was not located; however, maintenance records indicated that the cylinder head had not been removed in the 11 years and 317 flight hours prior to the accident.

Text from the NTSB. Open the NTSB docket for WPR10LA130 for the full record.