ATSB CRITICISES BOEING SAFETY INSPECTION AS
VIRGIN 737 ROLLS RIGHT
written by Adam Thorn | December 19, 2022
Left: Fatigue region 1 on the failed programming roller cartridge. Right: The Virgin 737-800, VH-YFZ
The ATSB has
criticised Boeing after it emerged a common cracking issue on its 737 wing
flaps is not included in the standard safety inspection recommended for the
aircraft.
Australia’s safety
investigator discovered the problem after a Virgin aircraft rolled to the right
during a flight from the Gold Coast to Sydney in April 2022.
The ATSB said the
aerospace giant “does not agree” that the particular issue with fatigue cracks
requires safety action because it has never led to an accident.
However, the ATSB
has urged Boeing to reconsider, arguing that any “reduction in safety margins”
for passenger-carrying aircraft warrants improvement.
“A detailed
inspection of the flap actuation system already exists, and while it includes
the aft flap rollers, it does not include the cartridges that house them,” said
the ATSB’s chief commissioner, Angus Mitchell.
“Inclusion of the
cartridges in the detailed inspection would provide the greatest opportunity
for fatigue cracks to be identified prior to failure.”
It comes after the
ATSB released the results of an investigation that found multiple occurrences
involving fatigue cracks and failures on 737 wing flaps in a location not
included in the detailed flap actuation system inspection.
The investigation
stemmed from an incident involving a 737-800, VH-YFZ, flying earlier this year.
“Immediately after
take-off, the pilot noticed the aircraft tended to roll to the right, and so
trimmed the rudder to keep wings level,” Mitchell said.
The aircraft no
longer required trim when the flaps were retracted for cruise, but the issue
returned when the flaps were extended for landing into Sydney.
“A walk-around
inspection after the flight found the outboard aft flap on the left wing had
not completely retracted, and a subsequent inspection found several components
in the aft flap actuation system had failed,” Mitchell said.
The ATSB determined
that a pre-existing fatigue crack progressed through the aft flap’s inboard
programming roller cartridge, resulting in component failure.
“The last general
visual inspection had been carried out on VH-YFZ’s left outboard flap,
according to Boeing’s specifications, in October 2020, and no defects were
found,” Mitchell said.
“While it could not
be determined whether the fatigue crack was present at that inspection, 10
other instances of cracking and/or failure of the programming roller were
reported to Boeing between 2017 and 2022, and at least six of these were old
enough to have been inspected several times prior to failure.
“Significantly, the
area in which the fatigue cracks developed was not included in the detailed
inspection that Boeing specified for the flap actuation system.”
The ATSB said that
Boeing has advised that it does not agree that this issue warrants safety
action – noting that a review of prior failures showed that aeroplane-level
effects were correctly mitigated by flight crews, and the affected aircraft
landed without further incident.
Nonetheless, the ATSB has issued a
safety recommendation to the planemaker to take action to increase the
detection of the fatigue cracks.
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