VH-TJU Boeing 737-476

Report On VH-TJU - Following Overhaul By An Overseas Maintenance Repair Organisation - 2008

The MRO (Maintenance Repair Organisation) had assessed an engine pylon crown bearing as serviceable, even though approved inspection data showed that it required replacing. The MRO had changed bearings before but there was some doubt as to its expertise and capability of repairing the lug in which the bearing was inserted. As a result, technicians from the operator’s machine shop travelled to the MRO at the request of operator LAMEs to carry out both the bearing change and lug bore inspection/repair.

The MRO’s docking lacked personnel safety features such as handrails and proper flooring in some locations. This had been brought to the attention of the operator’s management. The visiting machine shop technicians requested safety harnesses and the erection of scaffolding around the pylon before they would carry out their work.

The lack, or minimal use, of personnel safety equipment by the MRO would have made performing maintenance tasks very difficult.

The majority of tasks that spanned a number of shifts were not progressively certified for, meaning that it would not be clear as to what maintenance had been done, or if defects had been found, during the completion of those tasks.

Many tasks were certified as having been completed, yet no work had been observed being carried out in that area to validate such certification. An example was a task that required a modification to be carried out on the horizontal stabiliser sliding seals. It was signed as being completed but no one had been observed working in that zone and a box containing parts to complete the task was noted near the work area as still unopened.

As a result of very few defects being recorded by the MRO, a defect list was compiled by operator LAMEs. The list was used to keep track of defects that had been detected by operator staff after the MRO inspection tasks had been certified as completed, i.e. these were defects that the MRO did not detect. The list contained approximately 93 items, many of which were structural or systems related. By the end of the check, the majority of these items had been rectified, although operator maintenance staff never saw the MRO’s paperwork to verify this.

A customer defect observation regarding corrosion on a wing skin was brought to the attention of the MRO after the task for the inspection of that area had been certified as completed, with no defects found. The corrosion was located at a previous repair, which had an identifying sticker next to it advising that an Engineering Advice applied to the repair. The MRO subsequently removed the new corrosion, apparently in accordance with approved data. However, when the operator’s engineers inspected the new repair, they found that a hole, previously containing a protruding head fastener, now contained a counter-sunk fastener instead. It was determined that the counter-sinking process had resulted in a knife edge in the wing skin and damage to the underlying support structure.

The inappropriate repair was pointed out to the MRO, who at first did not believe that a problem existed. When they eventually contacted Boeing for repair details, not all the information was provided to Boeing for it to make a proper assessment of the repair required. This was detected by the operator’s staff, who then contacted Boeing with more comprehensive details of the inappropriate repair. As a result, Boeing then required that the MRO-repaired wing skin be replaced. In short, the corrosion blend and repair process carried out by the MRO had damaged the wing skin beyond repairable limits, requiring its replacement.

During a CIR (Customer Inspection Requirement) of a horizontal stabiliser jackscrew that had been replaced by the MRO, an operator LAME noticed metal particles at the cable drum. An investigation revealed that a cable guard had been installed incorrectly, resulting in metal-to-metal contact between the cable drum and the cable guard. As the horizontal stabiliser is a primary flight control system, it should have been subject to independent inspections for correct parts installation and function, prior to thecustomer’sinspections.

An instrument used for avionics work was noted as not having a calibration sticker. The instrument was required to be calibrated yearly. The manual which contained that requirement was not held by the MRO. Although, in this instance, the instrument was found to be within calibration, the MRO had no idea of its calibration status nor did it have the latest manual revision to maintain the instrument.

At the end of VH-TJUs check at the MRO and just prior to a test flight, operator LAMEs discovered that a drip shield, normally installed in the electrical and electronics compartment, was missing. The test flight was suspended until the shield was found and installed. The MRO was reported to initially deny that a drip shield existed in that location. It was later found that the shield had been sent to process workshops for repairs. There was no documentation to show that the shield contained a defect requiring it to be repaired, nor that the shield had been removed and was required to be reinstalled.

A loose clamp on a waste drain tube for the forward toilet remained undetected following removal and reinstallation of the ball Shut-off Valve because a static leak check of the system was not performed. The aircraft maintenance manual required a static leak check to be carried out. As a result, a number of avionics boxes in the electrical and electronics bay were contaminated with water when the drain tube separated from the valve during a pressurisation check of the aircraft on the ground.

Operator staff observed the MRO regularly carrying out maintenance on the aircraft without the approved maintenance data. Some of the observations were for complex maintenance tasks that required many steps to determine the serviceability of the aircraft system.

When VH-TJU returned to the operator’s maintenance facility in Australia, it spent six days having rectification work carried out on it. The following is some of the reported work that was required to be carried out to make the aircraft serviceable:

The engine throttles were found to be staggered at various cruise settings and fault-finding resulted in the changing of a Mechanical Engine Control unit and a seized Variable Bleed Valve cable.

Cockpit 1L windshield was considered unserviceable due to the window’s optical quality and was changed. It had previously been assessed at the MRO as being serviceable. During the operator aircraft’ s check, another operator’s aircraft was in the same hangar and had been painted. VH-TJU suffered paint over-spray because it had not been protected. This overspray was later observed being removed from the top of the fuselage and the window may have been damaged at this time.

During the replacement of the windshield, incorrect string was found installed. This string is used to break the window’s edge sealant so that the need to use scrapers on the metal structure is minimised. Due to the new appearance of the sealant at windshields 1L and 1R, it is believed that the string was inserted at the MRO during general sealant repair work, especially at the time when 1R windshield was replaced. In any event, the string found embedded in the sealant was of a type unfamiliar to Australian-based maintenance staff.

Four stops attached to tracks for the cockpit crew seats were found to be installed incorrectly.

The red-coloured lines located on the main landing gear side struts, used as a visual check for the flight crew that the landing gears are down and locked, were misaligned. The crew would not have been able to positively determine that the gears were down and locked. The main landing gears had been spray- painted in-situ at the MRO and the red marks reapplied afterwards.

At the MRO, operator LAMEs found that the black lines on the main landing gear oleo struts, used to indicate if the strut-mounted doors have moved, were applied with what appeared to be felt-tipped pens instead of paint.

A clamp for a pressure seal on the auxiliary power unit duct that passes through the rear pressure bulkhead was found incorrectly installed. The aircraft’s check package contained inspection tasks which covered specific areas such as the bleed duct.

An over-length bolt, used to retain a seal on the vertical stabiliser trailing edge, was gouging a rudder leading edge access panel; however the rudder operation appeared normal up to this time. The bolt’s interference with the rudder should have been detected as part of zonal inspections at the beginning and end of the check, especially when rudder and vertical stabiliser access panels, including the gouged panel, were reinstalled.

VH-TJU was returned to service after six days of post-check rectification, but six weeks later was withdrawn from service because of unusual noises reported coming from the mid cabin area. Fault-finding revealed that the cabin overhead air distribution duct was leaking from various duct joints. At the MRO, a section of duct had been removed for access as part of an EI (Engineering Instruction) repair on the fuselage crown structure. However, the materials used for joining the reinstalled section of duct were not in accordance with aircraft maintenance manual instructions and as a result, the joints had developed leaks. A two and a half metre long section of duct was removed for workshops-based repairs. In addition, the remaining length of duct in the aircraft was inspected to check its condition and retention to the aircraft structure. This required the removal of nearly all the ceiling panels, some video monitors and shrouds, cabin chairs and the peeling back of insulation at various structural attach points.

The EI Task Card and instructions for the fuselage crown repair were examined. The instructions stated that the duct in this area needed to be removed for access. Although the Task Card was certified as completed, there were no entries describing what removal/re-installation access work had been carried out.

Because EIs were not part of the operator LAMEs’ CIR (Customer Inspection Requirement) tasks at the MRO, it was decided that the EI crown repair done by the MRO should be inspected. The internal and external inspections revealed a satisfactory repair.

VH-TJU was returned to service four days later.

Comment:

Qantas Maintenance Staff feel an ‘ownership’ of company aircraft and can easily recognise degradation in workmanship and work practices. The operator’s maintenance staff at the MRO were very busy doing as much follow-up checks of the MRO’s work as possible, to ensure the safety of the aircraft.

A major concern by the operator’s maintenance staff is what they may have missed, because they were working to a pre-arranged list of CIR inspections. As a result, they were not always on-site 24 hours a day. The problem of the cabin air distribution duct has vindicated their concerns.

With the huge effort that they put in, operator maintenance staff feel ashamed that they were not able to get the MRO to deliver an aircraft which was up to, or even near, the operator’s maintenance standards. In the end it was decided that it would be better to get the aircraft home where it could be worked on to get it up to an acceptable standard.