Stabiliser trim mechanism damage was discovered on a Boeing 737-800, caused by a rag that had been left behind during previous maintenance.
On 7 June 2013 a Boeing 737-838 operated by Jetconnect Limited was undergoing scheduled maintenance at Auckland International Airport, New Zealand. During an inspection of the forward electronics and equipment compartment area under the flight deck, metal filings were found next to the stabiliser trim cable drum. On closer inspection a rag was found trapped under the stabiliser trim cable windings on the forward cable drum.
The rag had made the cable windings bulge outwards, which caused the cables to contact the cable guides, creating the metal filings and damaging the guides. The rag had increased the cable tension of the stabiliser trim system, which resulted in damage to a number of cable pulleys through which it was rigged. The control cables had also started to wear through contact with the steel bolts that held the cable guide spacers in place.
The Transport Accident Investigation Commission (TAIC) found that it was highly likely the rag originated from the Qantas Sydney maintenance hangar, and that the presence of the rag trapped in the cable drum windings compromised the integrity of the aeroplane’s stabiliser trim system manual control.
The key lesson learnt from the inquiry into this occurrence was that all personnel must take care not to leave anything behind inside an aircraft after completing maintenance or cleaning tasks, especially in areas or near systems critical to flight safety.