What happened
The incident occurred during a local training flight departing from Washington-National Airport. While en route, a fire started in the number four engine. The crew attempted to extinguish the blaze but was unsuccessful. The captain contacted air traffic control to report the emergency and received authorization to return to the departure airport for an immediate landing.
During the final approach to runway 33, the structural integrity of the wing failed, causing the number four engine to separate from the airframe. Despite this catastrophic loss of part of the aircraft, the crew maintained control and completed a safe landing. All four members of the crew survived without injury. However, the severity of the fire damage sustained by the right wing resulted in the aircraft being declared damaged beyond repair.
Findings
Investigations identified specific mechanical failures as the root cause. The primary issue was a failure in the exhaust valve of the number two cylinder and the exhaust connection of the number one cylinder within the number four engine, which initiated the fire. A significant contributing factor was the inadequate sealing between the firewall and the nacelle skin, as well as between individual cowl panels. These gaps allowed the fire to spread into Zone 3, where it became uncontrollable.