Amateur-built M18 accident near Meridian, California, August 6, 2010

The NTSB's narrative final · quoted from the NTSB record

The turboshaft-powered aerial application airplane had just departed the airstrip when the pilot/owner heard a loud "crack," and the engine stopped developing power. He executed a forced landing in a water-filled rice paddy adjacent to the airstrip. After touchdown, the airplane nosed over onto its back. The non-U.S. designed airplane was originally manufactured and delivered with a reciprocating engine. About 18 years before the accident, that engine was replaced with a U.S. military turboshaft engine via a Federal Aviation Administration (FAA) field approval. About 15 years after the engine change, and 3 years before the accident, the FAA mandated that piston-to-turbine engine conversions required the use of either an amended Type Certificate or a Supplemental Type Certificate, and that field approvals were no longer appropriate. Detailed examination of the engine revealed that most of the power turbine blades were severely damaged or missing. Material analysis of the turbine components revealed that the first stage turbine blades failed due to short-term exposure to excessively high temperatures and that other turbine blades failed due to impact damage from the thermally-failed first stage blades. The combustor was equipped with multiple fuel vaporizers, nearly all of which exhibited significant long-term thermal damage. None of the vaporizers were within the operable damage limits specified by the maintenance guidance. The damaged fuel vaporizers altered the combustor exit temperature profiles, which precipitated the first stage turbine blade failures. Maintenance records indicated that the 600-hour inspection interval of the engine hot section had been exceeded at least twice in the 14 years preceding the accident, and that, at the time of the accident, the engine had exceeded the hot section overhaul interval by about 300 hours. In-service records for the failed components could not be located. Although they did not contribute to the accident, multiple irregularities with the airplane's maintenance documentation were discovered during the investigation.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.