Slovenian Investigation of ATR 72 Cabin Smoke Incident at Ljubljana (SP-SPE)

Incident Overview and Response On July 31, 2020, at 19:30 UTC, the crew of an ATR 72-202, registration SP-SPE, was conducting an instrument departure from Ljubljana Jože Pučnik Airport (LJLJ) via runway 12. During the climb, the crew received a warning on the annunciator panel indicating the presence of smoke in the flight deck. The pilots also independently observed smoke and detected an unpleasant odor. In accordance with the operator's Operations Manual and the aircraft manufacturer's instructions, the crew immediately decided to abort the flight and return to the departure airport. The aircraft executed a 180-degree turn and landed safely on runway 30 under visual meteorological conditions. A fire and rescue team, alerted by air traffic control, monitored the return and assisted the crew after the aircraft stopped and the engines were shut down. The team conducted a thermal camera inspection of the flight deck. ## Aircraft and Operational Details The aircraft was a twin-engine turboprop operated by SprintAir S.A. of Poland. At the time of the incident, the aircraft was airworthy and had no items listed on its Minimum Equipment List (MEL). The maximum takeoff weight was 22,000 kg. Both pilots were appropriately licensed with valid type ratings and held valid medical certificates for commercial operations. The investigation found no significant maintenance discrepancies that would have affected airworthiness. ## Findings and Damage Assessment Following the landing, the aircraft was found to be undamaged, but the source of the smoke and odor was identified. The investigation determined that the smoke originated from an avionics cooling fan equipped with a temperature sensor, located beneath the flight deck floor. The aircraft was declared inoperable after the event. No injuries were reported among the crew or passengers, and no other damage occurred.