I'm on the airplane, love it, but.....
Modifications to eliminate landing control anomalies
Boeing 757 operators will have to install control wheel damper as*semblies
and leading-edge vortex generators, or vortilons, to prevent roll
oscillations near touchdown, under a proposed US Fed*eral Aviation
Administration ruling.
The agency says 11 incidents have been reported where 757s experienced
unintended roll oscillations on final approach, just before landing. One
incident resulted in a nose gear collapse after a hard landing; another
involved a tail strike that ended in an aborted landing.
These roll oscillations occur when the pilot makes large, rapid movements of
the control wheel, and the aircraft does not respond as expected," says the
FAA in a notice of proposed rulemaking (NPRM). "Boeing has developed a
damper for the control wheel that reduces the likelihood of these roll
oscillations by providing resistive force to large, rapid control wheel
movements that exceed a set value."
Vortex generators can also reduce oscillations, the FAA says. "We have also
received flight-test data indicating that one potential cause of these
unintended roll oscillations occurs when airflow over the outboard
trailing-edge flap separates due to the movement of the spoilers resulting
from large control wheel inputs. Abrupt control wheel inputs to counteract
the resulting roll can lead to roll oscillations of increasing magnitude."
Boeing has developed vortex generators that "create vortices over the flap
surface and help to mitigate a sudden and premature airflow separation when
the flaps are set in landing configuration and the spoilers forward of the
flaps are deployed," says the NPRM.
The manufacturer has previously issued service bulletins recommending wheel
damper assembly and vortex generator installation.
The FAA notes that the proposed rulemaking is considered to be an interim
action, and that Boeing is "currently investigating an additional
modification that may further reduce or eliminate the unsafe condition...
Once this modification is developed, approved, and available, [the FAA] may
consider additional rulemaking."
Compliance is expected to cost between $4.8 million and $6.5 million for
installation of the wheel damper assembly on the 578 US-registered 757-200
derivatives, predicts the FAA. The cost for the 51 US-registered 757-300s in
operation is expected to be $588,000.
Vortex generator installations are expected to cost $2.1 million for
affected aircraft. The ruling will affect US-registered aircraft only. The
NPRM is open to public comment until 17 March.
From Flight Inernational......