As the crew of the Boeing 747-438 applied take-off thrust to begin a flight from Sydney to Los Angeles, a noise described as 'similar to an engine stall' was heard by all on the flight deck. After an immediate check of engine parameters revealed no abnormal indications, the crew elected to continue the take-off and subsequently heard no similar noises.
Sequence of events
As the crew of the Boeing 747-438 applied take-off thrust to begin a flight from Sydney to Los Angeles, a noise described as "similar to an engine stall" was heard by all on the flight deck. After an immediate check of engine parameters revealed no abnormal indications, the crew elected to continue the take-off and subsequently heard no similar noises.
During the climb phase of the flight, the Cabin Services Director advised the flight crew of a small area of damage to the right outboard trailing edge flap. The first officer then inspected the area and reported that he believed that the damage was the partial delamination of the composite flap section. All engine parameters, including vibration levels were subsequently rechecked and found to be normal. After discussions with ground maintenance personnel, the crew decided to continue the flight.
On landing at Los Angeles, inspection of the aircraft by ground staff revealed the loss of both left and right combustion fairing panels from the number-three engine. Indentation and scraping damage was found on the internal surfaces of the bypass airflow nozzle behind the combustion fairing. The damage to the trailing edge flap was limited to the area immediately behind the number three engine.
On the morning following the departure, while conducting a routine runway inspection, Sydney airport staff recovered four large aircraft parts from the undershoot area of runway 34L. Further items, including small fragments of composite material, clevis couplings and metal strips, were subsequently found during a walking inspection of the runway undershoot area.
Inspection of the items by the operator's engineering personnel confirmed the items to be the missing fairing panels from the Boeing 747.
The ATSB examined the items recovered from the runway to determine how they separated from the aircraft. The left and right combustion fairing panels were both extensively damaged, with the larger right panel having broken into two sections. Both panels showed evidence of having forcibly struck the internal surfaces of the engine nozzle assembly before being ejected to the rear by the bypass airflow of the accelerating engine.
The fairing panels were mounted onto the engine by a row of three hooks that engaged with recessed pins on the upper panel section. When mounted, the panels latched together at the base of the engine using an adjustable hook and clevis. A study of the fairing panel mounting and latching points showed evidence that the right panel was not engaged with the upper panel at the time it was ejected from the engine. All three mounting hooks were undamaged and showed no sign of having been forcibly pulled away from the upper fairing pins. In comparison, both latches and the forward hook from the left panel showed damage consistent with the connections being overloaded and pulled apart.
Damage to the trailing edge section of the right centre wing flap was consistent with an impact with the ejected combustion fairing panels. Witness marks pointing to a forceful impact surrounded the area of damaged composite material along the edge of the flap section.
Technical analysis report number 18/01 refers to this part of the investigation and is available on the ATSB website or from the Bureau on request.
The engine from which the fairing panels were lost was a Rolls-Royce RB211-524 model. The panels were part numbers UL26239 (right) and UL26237 (left), with the manufacturers illustrated parts catalogue identifying both items as made to incorporate service bulletin RB.211-72-4647. The manufacturer introduced bulletin 4647 in 1977 to combat combustion (gas-generator) fairings detaching because of incorrect fitting.
Examination of the fairing assembly during installation confirmed that it was possible to place the fairing panels in position around the engine without engaging the upper mounting hooks. The clamping action of the interlocking fire seal along the rear edge of the fairing panels allowed the items to stay in position without the support of the hooks. Latching action between the fairing panels was also unaffected.
When the panels were installed incorrectly, inspection of the upper connection points clearly showed a large gap between the upper and side fairings. Inspection of that area was difficult because of the restricted confines of the cold stream duct surrounding the panels. Platforms for use within the cold stream duct were available, however comment from maintenance personnel suggested they were rarely used. Testing the platforms showed a degree of instability in use and further restricted the access to the lower areas of the duct. Latching the fairing panels together with the platforms in place was difficult. The time taken to load, fit and then unload the platform sections, was also cited as a problem for maintenance personnel. The Boeing maintenance manual for the 747-400 aircraft requires the use of access platforms within the cold stream duct.
Documents provided by the operator showed that the flight from Sydney to Los Angeles was the first flight of the aircraft following release from scheduled maintenance. That maintenance (described as an `A' check) involved several tasks that required the removal and reinstallation of the combustion fairing panels from all engines. A further review of the records relating to the work conducted on the number-three engine showed that a "panels and fairings final fitment check" line item was present in the work instructions. That action was signed-off as completed by a licensed maintenance engineer. The engine had been subsequently ground run for five minutes at idle speeds, with no noted anomalies. Check sheets for the examination of engines after ground running incorporated eight specific inspections, including a check for correct installation and latching of the fairing panels. Those checks had also been signed-off as being satisfactorily completed.
Fitting the combustion fairing panels to RB211-524 engines was the subject of several work instructions produced by the operator. The instructions referred to the operator's minor maintenance manual and the manufacturer's maintenance manual, which provided both written and visual illustrations of how the panels were to be fitted. The need for inspection of mounting hook engagement after installation was also clearly stated, with clear warnings of the potential for incorrect installation and the damage that may result. Requirements for the use of INA (integrated nozzle assembly) access platforms were also included in the latest revisions of the manual, which were issued on February 18, 2001.
Technical examination of the combustion fairing panels found that the items were released and ejected from the number three engine because of incorrect installation during maintenance activities before the flight. Evidence showed that the right side panel was not engaged with the upper panel when the items were last refitted. That situation then allowed the free movement of the fairing sections to a point where they were caught by the bypass airflow and forcibly ejected, striking the right wing outboard trailing edge flap section. The examination did not identify any deficiencies in the manufacture or maintenance of the fairing mounts or latches that could have contributed to the release.
The design of the fairing panels allowed them to be fitted to the engine and latched without the mounting hooks being engaged. Visual cues that signal a lack of hook engagement are not obvious and require specific inspection to verify correct installation. Maintenance documents for the number-three engine of the incident aircraft indicated that those inspections were first carried out after work was completed and again after the engine was ground run. However, neither inspection identified the problem.
A possible reason for the failure to identify the incorrect installation of the combustion fairings was the reluctance of the operator's maintenance staff to use the cold-stream duct access platforms. Without the platforms in place, inspection of the panel mounts for the signs of incorrect installation is difficult. Platforms have not been used because of instability within the duct, time taken in fitting and limits in access to the underside of the engine core.
- The design of the RB211-524 engine combustion fairing allowed the individual panels to be installed without the proper engagement of the upper mounting hooks.
- During maintenance before the occurrence flight, the right side combustion-fairing panel was fitted to the number-three engine without the mounting hooks being engaged with the upper panel section.
- Inspections following maintenance work and subsequently following engine ground running did not identify the incorrectly installed panel.
Local safety action
Rolls Royce Ltd
Following the occurrence, the engine manufacturer released a short instructional video, explaining the methods for correct installation of the combustion fairings and stressing the need for checking the installation once the panels are fitted.
The engine manufacturer also indicated that the design of the fairing panels was being revised to incorporate a baulking feature that will prevent the panels from being installed without the upper hooks engaged.
Qantas Airways Ltd
The operator has introduced a dual inspection requirement for cowling installation and latching. The procedure will be performed during main base maintenance visits until the manufacturer implements a mechanical baulking feature.
Australian Transport Safety Bureau safety action
As a result of the investigation, the Australian Transport Safety Bureau issues the following recommendations:
The Australian Transport Safety Bureau recommends that Rolls Royce Ltd expedite the development, trial and implementation of a suitable engineering solution to prevent the mis-installation of combustion fairings on RB211-524 and RB211-22B engines.
|Date:||24 April 2001||Investigation status:||Completed|
|Time:||1720 hours EST|
|State:||New South Wales|
|Release date:||12 February 2002|
|Report status:||Final||Occurrence category:||Incident|
|Highest injury level:||None|
|Aircraft manufacturer||The Boeing Company|
|Type of operation||Air Transport High Capacity|
|Damage to aircraft||Minor|
|Departure point||Sydney, NSW|
|Departure time||1720 hours EST|
|Destination||Los Angeles, USA|