Boeing 757 operators will have to install control wheel damper asÂsemblies and leading-edge vortex generators, or vortilons, to prevent roll oscillations near touchdown, under a proposed US FedÂeral 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.â€
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.â€
Flight International
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.â€
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.â€
Flight International
