What happened
On August 27, 2019, an IndiGo Airlines A320-271N, registration VT-ITB, was operating a scheduled flight from Delhi to Hyderabad with 159 passengers and six crew members. During the approach phase, approximately 30 miles from the top of descent, the flight crew reported hearing a humming sound in the cockpit, which they initially suspected was originating from the right-hand engine. This was followed by an audible thud and the appearance of perceptible smoke in the flight deck.
Upon noticing the smoke, the crew confirmed a burning smell was also present in the passenger cabin. The pilots donned oxygen masks and declared a "MAYDAY" to Chennai ATC, requesting an immediate descent and direct routing to Hyderabad. To manage the situation, the crew performed procedures from the Quick Reference Handbook (QRH). By switching off Air Conditioning Pack 1, the crew successfully reduced the intensity of the smell in both the cockpit and the cabin.
Following a coordinated descent through various flight levels, the aircraft landed safely at Hyderabad Airport at 11:46 UTC. Although firefighting vehicles accompanied the aircraft to the stand, no fire was found, and all passengers were able to disembark without injury.
The investigation
The AAIB India investigation focused on the serviceability of the aircraft and the crew's response to the ECAM alerts. Post-flight inspections revealed that the Blower Fan (Part No. EVT3454HC) within the Avionics Ventilation System had failed. The investigation also noted that the Avionics Vent Filter cartridge was dirty and required replacement.
Analysts examined the aircraft's ventilation configuration during the incident. Initially, the crew set the Vent Blower to the override position. However, because the system remained in a closed-circuit configuration, the smoke was being recirculated through the mixer unit into the cabin. It was only after the crew subsequently set both the Blower and Extract pushbuttons to the override position—placing the system in an open-circuit configuration—that the smoke was successfully exhausted overboard.
Findings
- The primary cause of the incident was the failure of the Blower Fan within the aircraft's Avionics Ventilation System.
- The crew initially suspected an engine issue due to the noise and smell, despite all engine parameters remaining within normal limits.
- The failure of the Blower Fan (Part No. EVT3254HC) was identified as a component that had previously caused similar incidents in the airline's fleet between 2016 and 2019.
- The aircraft was fully airworthy and maintained according to the approved program at the time of the event.