New Zealand’s Transport Accident Investigation Commission (TAIC) called upon the expertise of the country’s Wool Testing Authority and US National Transportation Safety Board (NTSB) to determine the origin of a rag found in the electronics and equipment compartment area under the flightdeck of a Qantas Boeing 737-800.
The rag was discovered during a routine maintenance check of the 737-800 ZK-ZQG at Auckland Airport on June 7 2013 after metal filings were seen next to the stabiliser trim cable drum, according to the TAIC report published on Thursday.
The rag had been trapped under the cable windings, causing the cables to bulge outwards and rub against the steel bolts that held the cable guide spacers in place.
“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 TAIC said.
“The integrity of the aeroplane’s stabiliser trim system manual control was compromised. Whilst considered unlikely, there was the potential for the stabiliser trim system manual control to become jammed or at worst disabled if a cable severed.”
However, the TAIC noted the electric side of the stabiliser trim control would still have operated through independent electric switches on the pilots’ control column.
The rag was sent to the NZ Wool Testing Authority to determine the type of material it was made from and how it had been manufactured.
The TAIC also obtained samples and photographs of the rags used by companies that did maintenance on the aircraft, which was owned by Qantas but operated by the company’s NZ subsidiary Jetconnect.
Also, it asked the NTSB to help Boeing test the rag to determine if it was introduced into the cable drum during the assembly of the aircraft in 2011.
While that test found the rag was “not consistent with examples used in production” at Boeing, the Wool Testing Authority’s findings showed Qantas’s Sydney base as the most probable origin of the ran.
“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 report said.
However, it was “not possible to determine when a rag may have been introduced into either the flightdeck or the electronics and equipment compartment, because the use of rags was not required to be controlled or recorded”.
The TAIC also noted a second incident involving a Jetconnect-operated Qantas 737 and a rag on September 11 2013, when the flightcrew of ZK-ZQC reported difficulty raising the right main landing gear after departing Melbourne bound for Wellington.
“The right main landing gear initially retracted but did not stay up, falling back down once the gear selector was moved to the off position,” the report said.
“When the crew reselected the gear lever to the up position, the right main gear retracted and stayed up.
“After the aeroplane landed at Wellington the ground engineers inspected the landing gear and found a rag wrapped around the right main landing gear uplock assembly.”
The report said a Qantas investigation found the rag was “used by an engineer to protect against an accidental head strike on the uplock during a maintenance task”.
“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,” the report said.
“Procedures developed to prevent foreign objects being left behind after maintenance must be adhered to in order to avoid similar incidents occurring in the future.”