What happened
On 24 August 2016, an ATR 72-212A, registration EI-FCY, was operating a scheduled passenger service from Birmingham, United Kingdom, to Cork Airport, Ireland. While approximately 52 NM east of Cork, the flight crew received alerts for electrical faults involving AC Bus 2 and Static Inverter 2. This was immediately followed by a Master Warning for electrical smoke, accompanied by visible smoke and a burning smell within the cockpit.
The crew promptly donned oxygen masks and declared a Mayday. Following the smoke checklist, the crew identified the smoke as electrical in nature. To manage the situation, the crew executed the Electrical Smoke checklist, which required switching off both AC Wild generators. This action led to the loss of both main hydraulic systems, necessitating a manual landing gear extension via gravity. Despite the high workload and the loss of various systems, including significant ice and rain protection, the smoke dissipated during descent. The aircraft landed safely at Cork Airport, and all 59 passengers and 4 crew members disembarked without injury.
The investigation
The AAIU examined the aircraft's electrical systems and the cockpit environment. The investigation focused on the source of the smoke and the consequences of the emergency procedures performed by the crew. Investigators analyzed the functionality of the static inverters and the impact of de-energizing the AC Wild generators on the aircraft's hydraulic and anti-icing systems. The investigation also reviewed the Quick Reference Handbook (QRH) used during the event.
Findings
- The smoke originated from a failure of a C602 capacitor within the number two static inverter.
- The failure caused the emission of electrical smoke, which entered the avionics ventilation circuit and was detected by the onboard smoke sensors.
- Following the Electrical Smoke checklist, the crew lost both main hydraulic systems, which required the landing gear to be extended manually and meant the gear could not be retracted after landing.
- The loss of the AC Wild generators also resulted in the loss of several electrical anti-icing components.
- The investigation noted that the crew faced a significant workload due to the loss of essential services and the necessity of performing multiple non-normal checklists.
Safety action
- The aircraft manufacturer has implemented a production change involving a new capacitor supplier and improved 'burn-in' processes for static inverters.
- A safety recommendation was made for the manufacturer to consider providing flight crews with specific guidance on how to safely reinstate electrical power to unaffected equipment following the use of the Electrical Smoke checklist.