Bombardier’s core lock screening procedure requires a cool-down period before engine shutdown to stabilize internal temperatures and clearances. However, this procedure does not produce the more severe thermal distress associated with the high power, high altitude flameouts that were experienced during the accident flight. As stated in the Safety Board’s November 20, 2006, safety recommendation letter to the FAA, the successful demonstration of Bombardier’s flight test procedure might not ensure that an engine will not experience core lock if the core is allowed to stop rotating after a high power, high altitude flameout. In its letter, the Board noted that the No. 1 accident engine had successfully passed the screening procedure during initial production acceptance testing.
2007 January 9, National Transportation Safety Board, “1.18.2 Core Lock”, in Aircraft Accident Report: Crash of Pinnacle Airlines Flight 3701, Bombardier CL-600-2B19, N8396A, Jefferson City, Missouri, October 14, 2004, archived from the original on 15 March 2022, pages 37–38