Modern jet engines, both the turbofan and turboprop variants used in most current generation aircraft, are extremely reliable. These engines are subject to regularly scheduled inspections and maintenance and are designed for operational lifespans in the thousands of flight hours. However, as is the case with any piece of machinery, these engines can fail. Catastrophic failures, either contained or uncontained, occasionally occur and may result in an associated fire. Engine malfunctions or component failures can also occur and these can require that the crew shut down an engine in flight.