What happened
On December 23, 2018, an ATR-72-212A, registration PR-AQZ, was operating a passenger transport flight from Recife to Maceió. While the aircraft was descending through 12,500 feet, the crew identified noises and sparks emanating from the electrical rack located behind the copilot's seat, followed by the appearance of smoke.
The smoke became intense, spreading into the cockpit and the passenger cabin. The crew immediately donned oxygen masks and declared a 'MAYDAY' to air traffic control. Following the Quick Reference Handbook (QRH) procedures for electrical smoke, the crew accelerated their descent and prioritized an approach to Maceió. The flight attendants managed the cabin, keeping the 48 passengers and four crewmembers calm during the emergency. The aircraft landed safely at Zumbi dos Palmares Aerodrome without further incident, and all occupants disembarked unharmed.
The investigation
CENIPA's investigation focused on identifying the source of the smoke and the cause of the electrical malfunction. The investigation involved technical analysis of the aircraft's electrical system, specifically the static inverters used to provide alternating current. Investigators examined the hardware and coordinated with representatives from the aircraft manufacturer and the inverter manufacturer.
Upon inspecting the electrical rack, investigators found that the damage was localized to the static inverter installed in position #1. The aircraft's electrical synoptic page had displayed an 'INVERTER FAULT' message during the event. Detailed disassembly of the unit revealed that a specific component, the C601 capacitor on a printed circuit board, had experienced overheating and partial melting, which produced the smoke and sparks.