What happened
On 26 February 2020, an Airbus A321-211, registration G-POWN, was involved in a serious incident at London Gatwick Airport. Prior to the event, the aircraft had undergone base maintenance involving a biocide treatment to address fuel contamination. During subsequent flights between Stansted, Krakow, and Gatwick, the aircraft began exhibiting unusual engine characteristics.
During the flight on the day of the incident, the crew encountered engine-related alerts. While operating at Gatwick, the aircraft experienced engine-related issues that required troubleshooting. The investigation focused on the sequence of events following the maintenance work and the subsequent operational flights that preceded the primary incident.
The investigation
The AAIB examined the maintenance history of G-POPM, specifically focusing on the biocide treatment process. The investigation reviewed the procedures used for the application of Kathon biocide and compared them against the approved maintenance manuals. Investigators also analyzed the transition between different maintenance data applications, specifically the shift from AirN@v to airnavX, to determine if the digital interface contributed to any procedural errors.
Technical examinations were conducted on the aircraft's engines, specifically the CFM56-5B3/3 units. The investigators inspected the Hydro Mechanical Units (HMUs) and analyzed deposits found within them. Furthermore, the investigation looked into the maintenance data interface design and how troubleshooting procedures for engine stall messages were presented to engineers.
Findings
- The investigation established that a biocide overdose occurred during the maintenance process, where an excessive concentration of Kathon was introduced into the fuel system.
- The excessive amount of biocide led to the presence of deposits within the engine Hydro Mechanical Units (HMUs).
- The maintenance engineer utilized a maintenance data application interface that presented troubleshooting procedures in a way that could lead to the selection of incorrect procedures.
- There was a significant transition occurring between the AirN@v and airnavX maintenance data systems, which impacted how information was accessed and interpreted.
- The investigation identified that the biocide concentration was much higher than the intended levels for moderate contamination treatment.