Mcdonnell Douglas Helicopter 369E accident near Casa Grande, Arizona, June 25, 2013

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

Before the accident flight, maintenance personnel exchanged the helicopter's air inlet barrier filter system, during which the engine was removed from the helicopter. A preflight inspection was completed before departure of the postmaintenance check flight, and no discrepancies were noted. The engine start and pretakeoff checks were normal, and, after departure, the flight appeared to progress normally. About 1 to 2 minutes after completing an in-flight power check, the pilot heard a "distinct loud pop." Subsequently, the engine lost total power, and the pilot entered an autorotation. The helicopter landed hard, its right skid collapsed, and it rolled on its right side. A postaccident examination of the helicopter's engine air inlet found that cloth material had been ingested into the engine air intake. During further examinations, more cloth material was found in the engine in a sufficient quantity and location to block the airflow through the engine and cause it to flame out. The cloth material found in the engine was consistent with maintenance rags found in a box at the operator's hangar facility. It is likely that, during the maintenance of the helicopter's engine, maintenance personnel covered vulnerable areas of the engine with shop rags to prevent contamination, and, during the reinstallation of the engine, they did not remove all of the shop rags. The engine then ingested the rags during the postmaintenance test flight. Due to the installation of the engine air inlet barrier system, the shop rags would not have been visible during the preflight inspection nor could they have made it into the engine from the outside of the helicopter with the system in place.

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.