Jetconnect B738 at Sydney and Auckland on Jun 7th 2013, rag damages stab trim system
Last Update: March 25, 2015 / 22:13:54 GMT/Zulu time
The aircraft subsequently was scheduled for regular maintenance. Maintenance engineers found metal filings next to the stabilizer trim cable drum in the forward electronics and equipment compartment underneath the flight deck. While investigating about the origin of the metal filings maintenance found a rag had been trapped under the windings of the stabilizer trim cable on the forward cable drum. The inspection found that the rag had caused the windings to bulge outward and contact the cable guides causing the metal filings. In addition the rag had caused an increased cable tension, which caused damage to a number of cable pulleys which rigged the cable. In addition the control cables had started to wear through contact with the steel bolts that held the cable guide spacers in place.
Both trim cables, four cable pulleys and the forward trim cable drum were replaced, the trim system rigged and tested before the aircraft returned to service.
New Zealand's TAIC released their final report releasing following findings:
- The integrity of the aeroplane’s stabiliser trim system manual control was compromised by a rag that became trapped under a control cable that was wound onto the forward cable drum of the stabiliser trim system.
- It was highly likely that the rag ended up in the aeroplane’s electronics and equipment compartment following cleaning, inspection, or maintenance conducted at the Qantas Sydney maintenance facility.
The TAIC reported that the fault was identified on Jun 7th 2013 and reported to the TAIC on Jun 8th. The TAIC subsequently opened an investigation, investigators travelled to Auckland to examine the parts removed from the aircraft and interview staff of the airline.
The rag was sent for analysis, the NTSB was involved to check whether the rag could have ended up in the cable drum during assembly of the aircraft in 2011.
The TAIC reported that while the investigation into the occurrence was in progress, the TAIC learned of another incident involving a Jetconnect Boeing 737-800 ZK-ZQC at Wellington on Sep 11th 2013, see Incident: Jetconnect B738 at Melbourne on Sep 11th 2013, right main gear did not lock up, which identified a rag at the right main gear assembly had interfered with the gear retraction.
The NTSB told the TAIC after completing the checks at the Boeing facilities that the rag submitted was not consistent with rags used at the Boeing facilities.
The TAIC subsequently collected samples from all other maintenance facilities that the aircraft had undergone maintenance at. A sample obtained from the Qantas maintenance facility in Sydney was found matching the occurrence rag.
The TAIC analysed: "The findings of the New Zealand Wool Testing Authority and the fact that the Sydney maintenance facility was the only one where that type of rag was used, make it highly likely that the rag found trapped on the forward cable drum originated from the Sydney hangar. The aircraft maintenance history was reviewed to establish when the rag had been trapped on the forward cable drum. However, this was not possible to determine, and no significant maintenance had been performed on the stabiliser trim system prior to the occurrence. There are a number of maintenance and cleaning tasks carried out in the flight deck area and in the electronics and equipment compartment. It was not possible to determine when a rag may have been introduced into either the flight deck or the electronics and equipment compartment, because the use of rags was not required to be controlled or recorded. Several aircraft system components and control units are located in the electronics and equipment compartment. Consequently there are many tasks carried out during routine aircraft servicing and maintenance that require engineers to enter the compartment and work in the area around the stabiliser trim cable forward drum. It is possible that an engineer carried a rag on them while working near the trim cables, which was either left behind or dropped and later became drawn onto the forward cable drum and under the cable windings."
This article is published under license from Avherald.com. © of text by Avherald.com.
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