Investigating Complex Factors
By Trudy McInnis
There
has been an aircraft accident. Debris from the wreckage is
scattered throughout a 200-metre radius. Tragically, the aircrafts
crew and its passengers have been fatally injured. The sound of
sirens permeates the scene as police and ambulance services attend.
Soon, media representatives arrive to speculate as to its causes
with cameras poised to document the wreckage.
That this could happen so suddenly and wreak such devastation
strikes at the heart of many people. An occurrence like this is
always associated with a sense of urgency to understand its
underlying features. But aircraft accidents are commonly
attributable to a complex interaction of many factors and on-scene
speculation rarely resembles the final conclusion. Often, long
after commotion surrounding an accident has dissipated, a team of
highly skilled experts continues to investigate the reasons for its
occurrence and uncover the events that preceded it.
Scientific analysis of evidence
The interpretation of evidence resulting from an occurrence can
require scientific analysis. This is the role of the Technical
Analysis Unit of the ATSB, which investigates, often in painstaking
detail, any structural, mechanical or operational factors related
to aircraft accidents or incidents.
Failures of propulsion systems, landing gear or flight control
structures, fractures in crankshafts, engine rods or turbine fan
blades, abnormal aircraft speeds or flying operations are just some
areas of investigation undertaken by the Unit.
Because there are myriad potential causes of aircraft safety
breaches, the team of specialists working in the Unit approaches
each occurrence with an assumption that it is unique.
"Investigations are rarely the same" said the Units Team Leader
Dr Arjen Romeyn. "There are always new issues, new understandings
to be gained. What were trying to do, ultimately, is get specific
answers to questions surrounding an occurrence."
Questions can include: what was the mode and sequence of
failures?; have all components performed to their specifications?;
what were the mechanical settings at the time of the occurrence?;
what results does analysis of the residual matter furnish?
Flight recorder analysis
To answer such questions the team uses specialist equipment and
apparatus. The Unit has the capacity to download and analyse data
from all civil flight data and cockpit recorders (commonly referred
to as black boxes) fitted to Australian-registered aircraft.
Because of its ability to establish the sequence of events prior to
an accident, this undertaking can provide critical information.
This is particularly so in instances where accidents have resulted
in a negligible amount of recoverable aircraft wreckage or where
evidence is transitory, such as occurrences involving
windshear.
Even in situations where significant material evidence has been
recovered an investigation can be reduced by days, or even weeks,
through the retrieval of information from a flight data
recorder.
Equipment for this purpose includes specialised tape decks and
interfaces, and both hardware and software for signal processing
and enhancing.
A radio frequency-shielded audio room, designed to prevent
internal and external interference, preserves the integrity of
audio analysis activities. It is also in line with the Air
Navigation Act 1920, which affords protection to audio captured by
cockpit voice recorders from any individuals not directly
associated with its analysis, as part of an investigation.
The Unit is also equipped with advanced computer graphics
software with the capacity to convert recovered data into
three-dimensional animations. This capability can provide a
detailed graphic reconstruction of a flight, allowing the
examination of any sequence of events, from any perspective, and at
any time. The benefits of this technology were demonstrated in the
investigation of the much-publicised overrun of QF1 at Bangkok
Airport, which occurred on 23 September 1999. Animations of the
flight used for the investigation were subsequently aired on
commercial television.
Materials failure analysis
Often microscopic features provide corroborating or conclusive
evidence in the determination of failed components. They can also
be vital to the detection of manufacturing assembly, maintenance or
operational abnormalities, such as fractures in engine mechanisms
or defects in airframe components.
Microscopes utilised in the Unit include: a low-power stereo
microscope for general observation, which has the capacity for
magnification of up to 50 times; a reflected-light microscope for
the examination of the internal structures of materials, which has
the capacity for magnification of up to 1000 times; and a scanning
electro-microscope which magnifies from 14 to 300,000 times the
actual size of an object. In addition, this microscope has an x-ray
analysis facility for determining the chemistry of small material
items.
The team approach
According to Dr Romeyn, while the array of equipment used in the
laboratories is impressive, the Units most important assets are the
highly skilled investigators who staff it.
"There is a perception that, because we work in a technical
area, its the equipment that does the work and were just operators.
To do our job we need particular tools, but thats all they are. Its
the understanding of what the tools allow us to see thats
important", said Dr Romeyn.
Core skills necessary to undertake the work required of the Unit
include a high degree of understanding in the ways mechanisms
operate and their environmental affects, an appreciation of design
issues, an awareness of how structures function and the ability to
identify failure modes.
These skills are reflected in the academic backgrounds of the
Units five investigators which comprise advanced qualifications in
metallurgy, aeronautical engineering and electrical design
engineering. According to Dr Romeyn, however, while knowledge of
these areas is vital, it is not in itself sufficient.
"Safety investigative work is a complex system and its the depth
of understanding that is important. You dont gain that just by
doing a degree. Its a continual learning process and experience is
an essential component of the success of our work", said Dr
Romeyn.
Dr Romeyn also acknowledges the importance of contributions made
from other areas of speciality. In any investigation a range of
skills are applied and this is just one skilled area. It is very
important to talk to a wide range of people. Investigators with
expertise in such areas as cabin safety and human performance, as
well as individuals from the wider aviation industry, can be vital
sources of information. Its the coming together of experience that
provides the basis for fruitful investigation, said Dr Romeyn.
Often pro-active measures are initiated from work performed by
the team. On 13 October 2000, while on a climb out of Hobart, a
Boeing 737 experienced a dramatic malfunction in one of its engines
which caused a reaction consistent with explosion. The aircraft
landed safely and its pilot and passengers were unharmed. By
analysing the factors surrounding the incident, the team identified
deficiencies in a procedure used to repair cracks in turbine
blades. Pursuant to these findings, the operator of the aircraft
modified repair procedures to prevent recurrence.
According to Dr Romeyn, initiating such improvements to existing
safety defences is a critical aspect of the work of the Unit.
"In the context of our work, pro-active investigations are those
directed at events which havent threatened safety directly but have
the potential to do so. We know that little things can trigger big
accidents. In a way, we operate as independent auditors of the
aviation system", said Dr Romeyn.
Aircraft accidents and incidents can have significant, immediate
and long-term affects on those involved. The determination of
underlying factors takes time and months can lapse between an
occurrence and the official release of findings related to it.
However, investigations into occurrences, such as those undertaken
by the team of the Technical Analysis Unit, can furnish
illuminating explanations as to what went wrong and how safety can
be improved.