Introduction
On May 22, 2021, at 04:50 UTC, an Airbus A320-214 aircraft, registration LZ-FBC, operated by Bulgaria Air as flight FB8509 from Sofia, Bulgaria, to Sharm el-Sheikh, Egypt, experienced a serious incident during the climb phase. The aircraft, carrying 139 people, had departed from runway 27 at Sofia Airport. Approximately 10 minutes after lift-off, at Flight Level 225, engine No. 1 was shut down. The flight crew declared PAN PAN and returned to Sofia for a safe landing. No injuries or damage to persons or property were reported.
Factual Information
The aircraft, a 180-seat A320-214, had last flown on May 7, landing early on May 8. No technical issues were recorded in the Technical Logbook after that flight. During a scheduled maintenance inspection on May 18, 2021, a fuel leak exceeding 90 drops per minute was found from the main fuel pump of the left engine, necessitating its replacement. On May 20, 2021, Lufthansa Technik Sofia specialists replaced the fuel pump in their hangar, and the exchange was recorded in the Technical Logbook at 19:00 local time. No further faults were noted in subsequent inspections before the flight on May 22.
The flight crew consisted of a commander (serving as Pilot Monitoring), a co-pilot (Pilot in Command), and four flight attendants, plus a technician with ground functions. During the climb, at FL225, the crew observed abnormal engine parameters and shut down engine No. 1. They declared PAN PAN and coordinated with Air Traffic Control for a return to Sofia. The aircraft landed safely on runway 27.
Analysis and Conclusions
The investigation by the Aircraft, Maritime and Railway Accident Investigation National Board determined that the serious incident resulted from violations in the technological process by Lufthansa Technik Sofia personnel during the replacement of the fuel pump. Additionally, the crew did not comprehensively monitor engine parameters (rotor speed, exhaust temperature, and fuel consumption) during take-off and climb, and were unaware of the maintenance work performed on the aircraft prior to the flight. These factors were identified as root and underlying causes of the engine shutdown.
No safety recommendations were issued in the final report.