What happened
On 1 October 1998, an Airbus Industrie A310, registration 5B-DAX, was stationary at Stand E38 at London Heathrow Airport. The aircraft was engaged in a public transport operation and was preparing for passenger boarding when the First Officer observed smoke and sparks emanating from his side windscreen.
Emergency services were immediately notified of the situation. While the fire was able to self-extinguish without further intervention, the intense heat resulted in the windscreen developing multiple cracks. There were no injuries to the nine crew members on board, and no passengers were on the aircraft at the time of the event.
The investigation
Investigators focused their attention on the aircraft's windscreen heating system to determine why the component had overheated. The investigation centered on the windscreen heating controller, part number 6664157.
Upon removal, the controller was sent to the manufacturer for detailed analysis. The examination revealed that the unit's temperature detection thresholds were operating outside of the required tolerances. It was determined that a malfunction in this controller allowed high current to continue flowing to the heating element even after the aircraft had landed and completed its previous flight cycle.