What happened
On 7 June 2013, while undergoing scheduled maintenance at Auckland International Airport, a Boeing 737-838 operated by Jetconnect Limited was found to have foreign object debris (FOD) lodged in its flight deck area. During a routine inspection of the forward electronics and equipment compartment, technicians discovered metal filings near the stabiliser trim cable drum. Further investigation revealed that a rag had become trapped under the windings of the forward cable drum.
The investigation
The investigation focused on the physical damage caused by the trapped material and the origin of the debris. The presence of the rag had caused the cable windings to bulge, forcing the cables into contact with the cable guides. This friction produced the metal filings and resulted in damage to the guides themselves. Additionally, the rag increased tension within the stabiliser trim system, leading to damage to several pulleys used in the system's rigging. The investigation also noted that the control cables had begun to wear due to contact with the steel bolts securing the cable guide spacers.
Regarding the source of the debris, the Commission determined it was highly probable that the rag had been left in the aircraft at the Qantas Sydney maintenance hangar.
Findings
- The primary cause of the mechanical damage was the presence of a rag trapped within the stabiliser trim cable drum windings.
- The trapped rag compromised the integrity of the manual control for the aeroplane's stabiliser trim system.
- The incident caused physical damage to cable guides, pulleys, and the wear of control cables against steel bolts.
- The investigation also noted a separate, uninvestigated maintenance incident involving a Jetconnect aircraft at the Qantas Melbourne hangar in September 2013, highlighting a recurring need for procedural compliance.
Safety action
- Maintenance and cleaning personnel must ensure that no tools, rags, or other objects are left inside an aircraft following service tasks.
- Particular care must be taken in areas or near systems that are critical to the safe flight of the aircraft.