What happened
In November 2024, an Embraer 190, registration VH-UZD, experienced a failure of its left wing slat system. The issue originated during maintenance when the torque tube for the number 4 outboard actuator was refitted. The tube had not been pushed sufficiently onto the actuator's splined shaft, preventing the locking bolt from properly securing the component. Following 50 flights in active service, the torque tube disengaged, causing the slat system to fail. While the failure occurred, onboard protection systems ensured that the safety of the flight was only minimally impacted.
In a separate but similar occurrence around the same period, another Embraer 190, registration VH-UYB, experienced a failure of its left wing flap system. During heavy maintenance at a different facility, the torque tube for the number 2 flap actuator was incorrectly assembled. In this instance, the locking bolt failed to pass through the hole in the actuator’s splined shaft. After the aircraft completed 35 flights, the torque tube disengaged, leading to the system failure.
The investigation
The investigation focused on why these assembly errors were not caught during the maintenance process. In the case of VH-UZD, the two aircraft maintenance engineers (AMEs) performing the installation did not notice the error. Furthermore, both the Licensed Aircraft Maintenance Engineer (LAME) responsible for checking the work and the LAME performing the independent inspection also failed to identify the improper fitment.
A similar lack of detection was noted regarding the work performed on VH-UYB. The investigation found no environmental or physical factors, such as poor lighting or difficult access, that contributed to the mistakes; the work on VH-UZD was performed in a new facility with good lighting and eye-level access. Instead, the error was attributed to the difficulty in visually distinguishing an incorrectly seated tube, as the visible difference in the actuator spline was as little as 6.35 mm. Because the other torque tubes in the system were correctly installed, the subtle discrepancy in the faulty tube did not trigger an alert during inspections.
Findings
- The primary cause of the failures was the incorrect positioning of torque tubes on the actuator splined shafts, which prevented locking bolts from securing the components.
- Maintenance personnel failed to detect the errors during both the primary installation and the subsequent independent inspections.
- The subtle visual nature of the error—a difference of only approximately 6.35 mm—made detection difficult.
- Embraer has previously noted similar issues within the E170, E175, and E190 fleets, with five related occurrences recorded between 2005 and 2011.
- Although Embraer updated maintenance manuals in 2010 to include illustrations and a push-pull check to prevent such errors, these specific instances bypassed those safeguards.