What happened
On December 18, 2024, at approximately 1600 Alaska standard time, a Lockheed L-382C (Hercules), registration N403LC, was performing a scheduled cargo flight from St. Mary’s airport (KSM) to Ted Stevens Anchorage International Airport (ANC). While climbing through 22,000 feet, the crew heard a loud bang and experienced a rapid loss of cabin pressure. The crew, consisting of a captain, first officer, flight engineer, and a loadmaster, donned oxygen masks and descended to 13,000 feet.
Initially, the crew suspected a bleed air issue because there was no visible external damage. Following the Quick Reference Handbook (QRH), they deactivated all bleed air systems and continued toward Anchorage. Approximately 30 minutes before arrival at ANC, the crew noted torque fluctuations on the number three engine. Fearing a connection to the bleed air systems, they performed a precautionary shutdown of the number three engine. The crew declared an emergency with air traffic control and landed at ANC without further incident. There were no injuries to the four occupants.
The investigation
Post-flight inspections conducted by maintenance personnel identified a crack in the forward pressure bulkhead. This fractured section was sent to the NTSB Materials Laboratory for examination. The investigation included participation from the Federal Aviation Administration (FAA) and Lynden Air Cargo LLC, with specialized groups focusing on structures and the digital flight data recorder.