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.
Technical examination
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.
Assembly examination
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.
Maintenance records
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.