What happened
On 13 January 2015, an Asiana Airlines Boeing 747-400SF, registration HL7417, was operating a scheduled cargo flight from Oslo, Norway, to Incheon, Republic of Korea. While cruising at 35,000 feet approximately 190 km north of Novosibirsk International Airport, the flight crew observed sparks and smoke emanating from the lower area of the cockpit, specifically between the left-hand windows #2 and #3.
Upon detecting the smell of burning plastic and seeing the smoke, a relief crewmember utilized a fire extinguisher to suppress the flames. The primary pilots notified air traffic control and requested a diversion to Novosibirsk. To manage the aircraft's weight for landing, the crew dumped approximately 47,000 lbs of fuel. The aircraft landed safely at Novosibirsk International Airport with no injuries to the crew.
The investigation
An investigation conducted by the ARAIB examined the electrical components of the left-hand window #3. Investigators analyzed the terminal block screws and the physical condition of the window's power terminal. The investigation focused on why electrical arcing occurred and why the circuit breaker failed to trip despite the presence of smoke and heat.
Findings
- The investigation identified that the terminal insert fractured, which led to high-temperature electrical arcing across the break, igniting nearby combustible materials.
- The primary cause was an inappropriate screw length recommended by the Boeing 747-400 Aircraft Illustrated Parts Catalog (IPC). The manual incorrectly suggested using a long screw regardless of whether the window was an old or new design, making proper installation impossible.
- A contributing factor was the application of excessive torque by a maintenance technician during the installation of the window terminal block, which caused internal damage to the terminal insert that was not visually detectable.
- The circuit breaker did not trip because the electrical current consumption did not exceed the breaker's capacity, and the fault did not create a grounded short circuit.
- The aircraft had previously displayed non-failure messages related to the window bus-bar a week prior to the incident, but these were not effectively addressed.