ANALYSIS
The control difficulties experienced by the crew shortly after departure could
be attributed directly to the horizontal trim system operating in the reverse
travel sense to that commanded by the pilot in command’s (PIC) inputs
to the horizontal stabilizer trim switches.
The investigation determined that systemic failures present during maintenance
allowed the aircraft to be returned to service with a horizontal stabiliser
trim system that operated in the reverse sense. Further, this incorrect flight
control function was not detected during the pre-flight inspection by the flight
crew.
A task that was maintenance intensive and/or extended over several shift periods
involving numerous personnel required careful management in the co-ordination
of effort to ensure every requirement was addressed to safely return the aircraft
to an airworthy condition. In this incident there was a breakdown in this defence
through absent or poorly defined handover procedures, documentation and co-ordination
of the maintenance.
Disturbance of a flight control system during maintenance triggers the requirement
for an additional layer of defence in the duplicate inspection procedure. In
this incident the engineers were unsure of when the procedure was to be employed
and this lead to a breakdown of the defence. A clearly defined procedure in
the company maintenance control manual for invoking the duplicate inspection
would have ensured a duplicate inspection was prescribed, which in turn should
have identified the trim reversal prior to the aircraft’s release to service.
The aircraft provided the crew with an aural alert system with a known difference
from its fleet siblings. The perception by the pilot in command (PIC) of the
aircraft being inherently different, combined with a loading distraction at
the critical trim function check time in the pre-flight sequence, probably led
to a misinterpretation by the PIC of his response to the anomaly.
Once airborne and with the emergency in progress, the PIC established that
he had control, but neglected to consider selection of the trim system control
to the copilot’s control wheel as an option. This may have been as a result
of his decision not to manipulate the trim system any further due to possible
mechanical failure.
SAFETY ACTION
As a result of this occurrence, the aircraft operator took immediate action
and issued a company memorandum to all engineering staff clarifying the requirements
of Civil Aviation Regulation 42G in regard to flight control system maintenance
and inspections requirements. This memorandum reiterated the requirement for
duplicate inspections inclusive of all trim systems.
The aircraft operator also advised the ATSB that the maintenance control and
engineering procedures manuals had been revised and that the following corrective
action had been taken:
- a new engineering procedure has been introduced, which addresses hand over
of maintenance co-ordination of tasks between shifts that involve multiple
personnel across those shifts, and hand over procedures for maintenance tasks
between engineers completing separate portions of the one task.
- The Engineering Procedures Manual (EPM) has been revised to include procedures
for certification of stages of maintenance within a task and now incorporates
a procedure to identify when duplicate inspections are required, and ensures
the incorporation of duplicate inspection entries in maintenance documentation
for those tasks deemed by civil aviation legislation and company policy to
require them. This EPM Section also identifies personnel responsible for ensuring
that duplicate inspection requirements are invoked when maintenance activities
require them.
- All maintenance documentation has been reviewed and the layouts amended
to address the appropriateness of maintenance log sheets, work cards and other
such documents to facilitate these procedural changes.
The operator also advised that they had reviewed the company induction and
training program for maintenance engineers and now emphasise the sections of
the Fairchild Aircraft Maintenance Manual that relate to the pitch trim and
control maintenance practices. The sonalert unit in the aircraft was replaced
after the incident. This aircraft’s sonalert operation now conforms to
that of the operator’s fleet.
RECOMMENDATION
As a result of this and previous occurrences, the Australian Transport Safety
Bureau issues the following safety recommendation:
R20040078
The Australian Transport Safety Bureau recommends that M7 Aerospace Pty Ltd
review and amend its Fairchild SA-227 series maintenance manual to ensure that
notes on operational tests, with regard to horizontal stabiliser movement versus
trim switch position referred to in Section 27-40-10 for removal of the pitch
trim switch, are included in Section 27-10-10 for related maintenance activities,
or references to them are clearly noted in that part.