Despite almost 100 reported and unreported incidents of arcing, smoke, fire or overheating in the windshields of Bombardier Dash 8 aircraft since 2000, checklists and training for crews do not specifically address how to deal with the issue, according to a recently released factual report by the NTSB.
A June 5, 2015, incident involving a CommutAir Dash 8-200 flying as United Express Flight 4776 on the approach to Bradley International Airport resulted in an emergency landing, after which the passengers evacuated on a taxiway. There were no injuries.
While setting up for the approach, the crew heard a “popping” noise and noticed arcing on the right windshield terminal block in the upper forward corner of the windshield, according to the factual report on the incident. The block is integral to the windshield and is a component in the heating system.
The arcing produced what the first officer described as a “torch-like” fire and “loud hissing noise.” Both pilots donned oxygen masks, and the first officer attempted twice to put the fire out with an extinguisher, but the fire continued to reignite. “The fire flared back up and continued for an unknown amount of time before extinguishing itself while still producing smoke,” the NTSB said.
An FAA official who examined the aircraft noted that the windshield heat switch was in the NORM position, a setting that cycles the heaters to keep the windshields at 108F.
The NTSB said the emergency aircraft fire and smoke checklist for the aircraft provides instructions for diagnosing the source of a fire “but does not specifically mention the windshield heating system or terminal blocks” and does not instruct pilots to turn off the windshield heat switch. If pilots suspect an electrical fire, however, they are instructed to run the aircraft on essential power, which would mean shutting off the windshield heat. “There is no specific training provided for the crew for windshield arcing, smoke, fire or overheat events,” said the NTSB.
Investigators do not identify any particular failure of the terminal block, but note that the windshield had been installed at the factory in 1998. PPG Aerospace, the windshield manufacturer, says the average life of windshields is 8.2 years. “CommutAir does not track the life of the windshields in their fleet since they are replaced on-condition,” the NTSB said. CommutAir’s maintenance program calls for several inspections of the windscreen and terminal block, the most recent of which occurred in April 2013. At that time, the moisture seal for the terminal block was repaired.
The NTSB found 77 reports of events involving arcing, smoke, fire or overheating at the windshield terminal block since 2000, and PPG provided information on 17 additional windshields that were not reported in official service difficulty reporting systems. Bombardier had revised the aircraft maintenance manual in 2003 and 2005 to include information on mounting hardware for the power and sensor wires to the terminal block and has published several in-service activity reports on the issue “over the years,” said the NTSB.
Transport Canada in 2012 issued a civil aviation safety alert recommending detailed inspection of the windshield terminal blocks.