A Bombardier DHC-8-402 was in cruise flight, between Halifax and Montreal (Canada) on this day in aviation in 2018. Onboard 72 passengers, 2 cabin crew and 2 flight crew.
Area of heat damage at row 14 of the occurrence aircraft, shown with left cabin wall upholstery removed (arrow indicates electrical connector 9811-J711) ©TSB Canada
Flight preparation, take-off and climb till cruise flight level and the initial cruise flight were uneventful. However, at 09.22 lt (31 minutes after take-off), passengers alerted the cabin crew and informed them that they saw sparks terminating from behind the overhead luggage bin above seat 14A (left side of the cabin) and also observed a burning odour in the same area. The cabin crew immediately informed the flight crew and then returned to the area to further inspect it and if required carry out fire fighting tasks. However, on returning from the flight deck the sparking had stopped and the burning odour had started to dissipate. In the meantime, the flight crew had carried out the memory items related to the "FUSELAGE FIRE OR SMOKE" Emergency Checklist and donned their oxygen masks. ATC was contacted, an Emergency was declared and a diversion to Fredricton (Canada) was initiated in consult with ATC. Several caution lights were illuminated;
PITOT HEAT 1
ENGINE ADAPT HEAT 1
LEFT TRU
PUSHER SYSTEM FAIL
Some other caution lights had flickered momentarily but did not remain on.
While on the approach to Fredricton the aircraft flew into an area of icing, resulting in an Airspeed Mismatch and a yaw damper and autopilot disconnect (an Airspeed Mismatch is a fault triggered when indicated airspeed differs between the left- and right-side instruments) Knowing the #1 Pitot heat had failed the crew concluded these faults were a result of a blocked lefthand pitot tube, as a result of the Pitot Heat 1 failure. The aircraft was hand flown from that moment in time using the air data from the right-hand pitot tube. The remainder of the approach and the landing were uneventful the aircraft stopped on the runway and the passengers were told to immediately leave the aircraft via the passenger door onto the runway. A short while later they were transported by bus to the terminal.
Burn damage on connector 9811-J711 ©TSB Canada
The incident was investigated by the Transportation Safety Board of Canada., available by clicking here. The most likely cause for the incident was determined to be an incorrect bend radius on the wires, which induced a side load on the connector pins, resulting in the failure of the pin locking mechanism. Additionally, it was noted that some wires were twisted and crossed over each other as they transitioned from the strain relief backshell into the connector body. This may have contributed to additional stress at the pins of the connector. 9811-J711, causing the short circuit.
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