The Australian Transport Safety Bureau did not conduct an
on-scene investigation of this occurrence. The report presented
below was prepared principally from information supplied to the
Bureau.
REPORTED INFORMATION
On 13 March 2003, while on final approach during a training
flight, the crew of a Lear 45 aircraft, registered VH-SQR, reported
feeling a severe vibration through their respective control
columns, followed by a rapid 10 to15 degree nose-down pitch change.
Attempts to manually trim the nose of the aircraft up failed, with
both crew members required to pull back on the control columns in
order to regain control of the aircraft.
A subsequent inspection of the aircraft by the operator's
engineers revealed that the aircraft's horizontal stabiliser could
be moved by hand, vertically, approximately four inches at the
leading edge. On examination, the horizontal stabiliser actuator
appeared normal, with all attachments in place. However, the
actuator was found to have free movement of its shaft in and out of
the actuator body. Further detailed examination indicated that the
actuator's primary `Acme screw' had failed. With this screw failed,
the horizontal stabiliser load should have been retained through a
secondary rod, however, the threaded retaining nut had unscrewed
from the rod.
The United States National Transportation Safety Board (NTSB)
advised the Australian Transport Safety Bureau (ATSB) that they
were conducting an investigation into the failure of the horizontal
stabiliser actuator, and the ATSB appointed an Accredited
Representative to that investigation.
As a result of the incident, the US Federal Aviation
Administration (FAA) issued emergency Airworthiness Directive (AD)
2003-06-51, on 20 March 2003, requiring operators to conduct an
immediate inspection of Lear 45 aircraft horizontal stabiliser
actuators and to remove from service any actuators that were the
same part number as the failed one.
The Australian Civil Aviation Safety Authority issued
Airworthiness Directive 5/2003, on 21 March 2003, requiring all
Australian Lear 45 operators to comply with the requirements of the
FAA AD. Additionally, the actuator manufacturer completed a new
actuator design and has since had the new actuator certified for
fitment to all affected Lear 45 aircraft.
The US NTSB is yet to publish its final investigation report
(number ENG03WA011).