Cessna 172R N2478B accident near Oceanside, California

Probable cause

A total loss of engine power in flight due to the fatigue failure of the No. 4 cylinder.

NTSB analysis

The pilot made an off-airport forced landing following an in-flight loss of engine power. The No. 4 cylinder (left rear) fractured and separated circumferentially in the area where the head joins the barrel. Metallurgical examination identified a fatigue fracture primarily on the exhaust side of the cylinder head, perpendicular to the axis of the barrel. Its inner edge abutted the crest of the first thread on the barrel. Engine Components, Inc. (ECi), manufactured the cylinder. ECi issued Mandatory Service Bulletin (MSB) No.08-1, Revision 3, dated August 19, 2008. It stated that the purpose of the MSB was to alert their customers about possible fatigue cracking and head separations on a specified group of replacement cylinders for Lycoming parallel valve engines. Cylinders identified by specific serial number ranges were to be inspected and pressure tested or inspected and replaced at specified reduced life limits. On October 20, 2008, Federal Aviation Administration (FAA) Airworthiness Directive (AD) 2008-19-05 became effective and mirrored ECi's MSB serial number range and corrective actions. The AD stated that the intent was to prevent loss of engine power due to cracks at the head-to-barrel interface in the cylinder assemblies and possible engine failure caused by separation of a cylinder head. The cylinders from the accident airplane had serial numbers that were outside of the range listed in the MSB and AD. The FAA has issued a Notice of Proposed Rule Making (NPRM) that would revise the serial numbers covered by the AD to encompass an expanded population of affected cylinders. ECi has a design change that is pending FAA approval.

Text from the NTSB. Open the NTSB docket for WPR09LA145 for the full record.