What happened
On a scheduled cargo flight departing from Norman Wells, Northwest Territories, a Douglas DC-4, registration C-GXKN, experienced a significant mechanical failure during its climb. While ascending through approximately 3,500 feet, the crew noticed vibrations followed by a fire in the number 2 engine nacelle.
In response, the crew executed the Engine Fire Checklist, which involved feathering the propeller and discharging fire extinguishers. However, the fire continued to burn. During the emergency, the aircraft experienced an uncommanded feathering of the number 1 propeller and the unexpected extension of the main landing gear. While the crew initially prepared for an off-field emergency landing near Dot Lake, the fire eventually self-extinguished after the crew performed an Engine Securing Checklist, which included turning off the fuel selector.
The crew elected to return to Norman Wells Airport. During the approach, the aircraft's flaps could not extend beyond 10 degrees due to hydraulic damage. The aircraft landed on Runway 27 at a higher-than-normal speed. During the landing roll, the aircraft began to veer to the right and eventually departed the runway surface, coming to a stop in deep snow. There were no injuries to the four crew members, though the aircraft sustained substantial fire damage.
The investigation
The investigation focused on the source of the fire and the subsequent mechanical failures. Investigators determined that a fuel leak had occurred in the main fuel inlet line within the engine compartment. Although an Airworthiness Directive (AD 48-12-01) existed to mandate the replacement of this specific fuel line, the modification had not been implemented on C-GXKN.
Technical analysis revealed that the fire was able to persist because the primary Engine Fire Checklist did not require the fuel selector to be turned off; the fire only ceased once the crew performed the secondary Engine Securing Checklist. Furthermore, the investigation found that the fire had compromised the fuel line between the tank and the shutoff valve, rendering the firewall shutoff valve ineffective at stopping the fuel flow.
Findings
- A leak in the main fuel inlet line caused an in-flight fire in the engine nacelle and wing.
- The failure to implement a mandatory Airworthiness Directive for fuel line replacement allowed the leak to occur.
- The fire remained active for an extended period because the initial emergency checklist did not include shutting off the fuel selector.
- The fire caused hydraulic damage, leading to the uncommanded extension of the main landing gear and limited flap operation.