Air Canada Jazz DHC-8 Windshield Heater Fire

Incident Overview and Emergency Response On a flight from Cranbrook to Vancouver, British Columbia, an Air Canada Jazz de Havilland DHC-8-311 (registration C-FRUZ, serial number 293) operating as flight JZA8216 encountered an electrical issue. The aircraft was in instrument meteorological conditions with 3 crew and 33 passengers on board. During descent through 14,000 feet above sea level, the left forward windshield heater terminal block arced and caught fire. The flames lasted for a few seconds before extinguishing when the crew turned off power to the windshield heater. The inner pane of the windshield was shattered. An emergency was declared, and the flight landed at 1958 Pacific Daylight Time with emergency and rescue services on standby. No injuries were reported among passengers or crew. ## Operational Context and Crew Actions The flight departed Cranbrook with the windshield heat initially set to WARM. As the aircraft climbed through 1,000 feet above ground level, the outside air temperature reached -1°C and icing was encountered. The windshield heat was then set to NORMAL. The aircraft encountered cloud and light to moderate icing during climb, cruise, and initial descent. At 10,000 feet above sea level, the aircraft was clear of cloud and the outside air temperature was -10°C. The surface temperature in Vancouver was 13°C. Both pilots were certified and qualified for the flight, with the captain possessing significant experience on type and in total. The flight deck and cabin crew handled the emergency in accordance with established procedures. The designated first officer was the pilot flying and remained at the controls throughout the occurrence. The captain attempted to use the fire extinguisher but had difficulty unlatching it from its mount on the bulkhead behind the captain's seat. By the time it was unlatched, the flames had disappeared and the extinguisher was no longer needed. The circuit breaker for the windshield heat system did not trip. ## Post-Landing and Cockpit Voice Recorder Issues The flight landed at 1958 and stopped on the runway. When the crew deemed it safe, the aircraft was taxied to the gate where passengers exited normally. The Transportation Safety Board (TSB) had been advised of the event as it was unfolding and asked that a message to secure the cockpit voice recorder (CVR) be relayed to the crew. The crew did not receive the message and, consequently, did not secure the CVR. The Air Canada Jazz Company Operations Manual (COM) requires that the CVR circuit breaker be pulled only after gate arrival on any flight leg during which an incident or accident has occurred. The CVR recorded only the last 30 minutes of sound from the cockpit. The emergency was declared at 1946 and the aircraft reached the gate at about 2008. The CVR could have had about 22 minutes of recordings relating to the event. Once parked, however, the aircraft was not quarantined and the operator's maintenance department proceeded to replace the windshield. During this time, power was applied to the CVR for more than 30 minutes and information that could have been valuable to the investigation was overwritten. ## Technical Investigation and Findings Cockpit windshields are not life-limited but are on-condition maintenance items. The Dash 8 Maintenance Manual and the component manufacturer, PPG Aerospace (PPG), publish condition limits for delamination, cracking, and damage. The occurrence windshield was manufactured in 1996 by PPG and had accumulated over 19,000 flight hours in the 9 years since its installation. The windshield and windshield heat controller were sent to the TSB Laboratory for examination. The windshield is a 3-ply laminate. The inner ply was cracked, but not the outer and centre plies. The windshield heat controller was tested and performed as designed. An arcing event could have been caused by faulty or aging conductive film in the windshield or by moisture-induced degradation. However, this would have caused the outer ply, not the inner ply, to break. Since the inner ply was the layer that had broken, the conductive film is likely not at fault. While the screw and ring terminal attached to the top L2 position on the terminal block were discoloured due to their proximity to the arcing and heat, they were not melted or physically damaged. There was no evidence of arcing between the screw, ring terminal, and L2 terminal. This indicates that there was likely good contact between the screw and L2 terminal. The lack of damage to the screw threads and the internal screw threads indicates that the screw had not been cross-threaded, which may have allowed the area to heat up or arc due to increased resistance in the connection. The burning and melting damage was mainly located at the edge and under side of the terminal block, indicating that the damage was not related to the external connection to the windshield. The origin of the arcing appears to be either a deterioration of the solder joint under the L2 connection on the terminal block or a damaged braid leading to the L2 connection. If the solder joint had failed, it could have separated allowing an arc to occur. If the braid had been damaged, it may have increased the resistance in the wire, heating it enough that it may have melted the solder. This would have resulted in a separation of the wire from the pad, allowing arcing to occur. A damaged wire could also have separated, allowing arcing between the wire segments. The high bus to bus resistance can be explained by the burning away of part of the wire leading to the L2 connector. While this would normally result in an open circuit, the charred remains created a conductive carbon path, completing the circuit with a higher characteristic resistance than a wire would. When the L2 terminal was extracted from the terminal block, the wire braiding that was soldered to the bottom of the terminal appeared to be in its originally installed position. The remnant of the braiding that was found soldered to the terminal pad was still folded and the bend was lined up with the edge of the terminal block. If the arcing had initiated at the braid connection at the L2 pad due to a loose or poor solder connection, it is most probable that the braid remnant would no longer be found in its original orientation, as the forces from the arcing would have moved the loose braiding around. The previously molten ball of metal found embedded in the patch of re-melted glass would have come from the missing portion of the braid that leads to the L2 pad. Therefore, it is most probable that the solder connection to the L2 pad was solid and that the braiding was damaged leading to the arcing event between damaged portions of the braid itself. It was not possible to examine the braid where the arcing had initiated as this section of the wiring had been vaporized. It was not possible to determine what caused the initial damage to the wire braid. As the glass melted in a small localized area where the arcing occurred, a high temperature differential was experienced and, as the melting had penetrated beyond the strengthened portion of the glass, the glass ply cracked. This indicates that the cracking was caused by the arcing. ## Safety Actions and Conclusions Air Canada Jazz has taken the following safety action: - Instigated an immediate Dash-8 fleet wide check of all heated transparency terminal block connections for proper torque, hardware, and installation. - Conducted a risk assessment of the fire extinguisher type and location. The company reported that the installation is standard on all its aircraft. Its findings indicated a low risk with no further action. - The DHC-8 Maintenance Schedule was amended to include a torque check of the windshield terminal block connections at each C Check (5500 hours). - Inserted specific guidance in its Emergency Response Manual regarding when to quarantine an aircraft and the requirement to pull the circuit breakers for the CVR/FDR, following an incident or accident. - The Jazz (pilot) Training Program Manual, section 6.16.2 now specifies that annual pilot training includes requirements for FDR/CVR deactivation. This training was introduced in response to Transport Canada Advisory Circular AC 700-013, published on 01 January 2010. This report concludes the Transportation Safety Board's investigation into this occurrence. Consequently, the Board authorized the release of this report on 05 January 2011.