Incident Descriptions
In November 2024, during maintenance on aircraft VH-UZD, the torque tube for the left wing slat number 4 outboard actuator was refitted. It was not positioned far enough onto the actuator’s splined shaft for the locking bolt to secure it. After re-entering service and completing 50 flights, the torque tube disengaged, causing the slat system to fail. Protection systems ensured the safety of flight was minimally affected.
Around the same time, another Embraer 190, VH-UYB, was under heavy maintenance at a different facility. The torque tube driving the left wing flap actuator number 2 was incorrectly assembled: the locking bolt had not passed through the hole in the actuator’s splined shaft. The torque tube disengaged 35 flights after the aircraft re-entered service, resulting in flap system failure.
Error Detection
The two aircraft maintenance engineers (AMEs) who fitted the torque tube on VH-UZD did not identify the incorrect fitment. The licensed aircraft maintenance engineer (LAME) checking this work and a second LAME carrying out an independent inspection also failed to detect the error. Similarly, the error on VH-UYB went undetected by those performing and certifying the work.
Investigators found no physical or environmental factors that may have influenced the incorrect assembly. The work on VH-UZD occurred in a new facility with good lighting, and access to the work area was good, with components at eye level. It is likely that the error was not detected because the subtle difference in appearance of an incorrectly assembled slat torque tube (as little as about 6.35 mm more of the actuator spline visible) was not recognized by the two AMEs and two LAMEs involved. Additionally, the remaining torque tubes in the slat drive system were correctly assembled, but their subtly different appearance did not trigger recognition that the original torque tube was incorrectly assembled.
Background Information
Installation of slat and flap drive system torque tubes is a simple task, but errors have occurred. Embraer reported that from January 2005 to August 2011, in the worldwide fleet of Embraer 170, 175, and 190 aircraft (which share similar componentry), there were five occurrences related to incorrect torque tube installation. The Embraer 190 has 24 locking bolts in the slat drive system and 18 in the flap drive system, totaling 42 opportunities for incorrect assembly.
In 2010, Embraer amended the aircraft maintenance manual to reduce the possibility of assembly errors. These amendments aimed to remove residual torque loads during removal and installation by releasing the power drive unit brake, highlight the possibility of error with an illustration, and provide a means to detect an installation error through a push-pull check. These changes were communicated in multiple documents, such as a service newsletter, available to operators and maintainers of E190s. Review of such documents can assist in highlighting known issues and prevent reoccurrence.