Incident
On December 18, 2024, at about 1600 Alaska standard time, Lynden Air Cargo LLC flight LYC141, a Lockheed L-382C (Hercules) airplane registered as N403LC, suffered a rapid decompression while climbing through flight level 220 (22,000 feet) after departing from St. Mary's Airport (KSM) in St. Mary's, Alaska. The flight was a regularly scheduled cargo operation under Title 14 Code of Federal Regulations Part 121, destined for Ted Stevens Anchorage International Airport (ANC).
Flight Actions
The flight crew consisted of a captain (pilot monitoring), first officer (pilot flying), flight engineer, and a load master. Upon hearing a loud bang and experiencing loss of pressurization, the crew donned oxygen masks and initiated a descent to 13,000 feet mean sea level. With no visible signs of damage, they suspected a bleed air issue and turned off all bleed air systems per the quick reference handbook. The flight continued toward Anchorage.
About 30 minutes before arrival at ANC, the number 3 engine's torque began to fluctuate. Concerned the fluctuations were related to the bleed air systems, the crew performed a precautionary shutdown of that engine in accordance with Lynden Air Cargo's procedures. An emergency was declared with air traffic control, and the flight landed without further incident.
Inspection
Post-flight inspection by maintenance personnel revealed a crack in the forward pressure bulkhead. The fracture was removed and sent to the NTSB Materials Laboratory for further examination. The aircraft sustained substantial damage.
Investigation
The National Transportation Safety Board (NTSB) invited qualified parties to participate in the investigation, including the Federal Aviation Administration (FAA) and Lynden Air Cargo LLC. Specialized investigative groups were formed, focusing on structures and the digital flight data recorder (DFDR). The investigation remains ongoing.