Sequence of events1
On 19 July 2004, the owner-operator pilot of Bell Helicopter
Company 47G-3B-1 Soloy2 helicopter, registered VH-RTK, was
contracted to spray herbicide on a property near Wodonga,
Victoria.
Early in the day, the pilot and the company operations manager
met with the property owner to discuss the proposed work. The
discussion included the identification of known powerlines, other
hazards, and sensitive areas likely to affect the operation.
Shortly before the discussion, the operations manager showed the
pilot the known primary powerlines in the general area where the
spraying and loading was to be conducted.
Later that morning, the loader/driver of the chemical and
re-fuelling truck arrived at the proposed replenishment point. The
pilot positioned the helicopter at the replenishment point at about
midday and commenced the final preparations for the day's spraying
operations. The preparations included an aerial survey, in the
company of the property manager, of the areas to be sprayed. During
that flight, the property manager indicated to the pilot the areas
that were free from powerlines, including a valley that he
considered a safe transit zone between the replenishment truck and
the proposed spray area.
The pilot commenced spraying operations on the occurrence
property at about 1458 Eastern Summer Time. Shortly before 1512,
the property manager heard the helicopter returning to the
replenishment point from an unexpected direction and not from the
direction of the identified safe transit zone.
The property manager reported that he observed some 'glitter'
emanate from the helicopter, before it then descended and
disappeared into heavily timbered terrain. No radio broadcasts were
made by the pilot to air traffic services, or to the loader/driver
to signify that an emergency had occurred.
The helicopter impacted terrain about 860 m to the south-west of
the replenishment point, and was destroyed by impact forces. The
pilot, who was the sole occupant, was fatally injured. There was no
fire.
The loader/driver notified the company operations manager, then
commenced to search for the helicopter. The company operations
manager notified emergency services, and they arrived at the
accident site about 20 minutes later.
A two-cable electric powerline was found severed at a point
approximating that at which the property manager reported seeing
'glitter' come from the helicopter. There was no other property
damage.
The powerlines struck by the helicopter during the approach to
the replenishment point consisted of two parallel three-strand
lightweight high-tensile steel cables, each of 2.75 mm diameter.
The powerlines had been erected several years previously, and were
located on the north-eastern side of a ridgeline, strung across the
direct track from the last treatment area to the replenishment
point.
The powerlines were not depicted on the relevant aeronautical or
topographical charts. They were not connected to the power supply
grid and had developed a dull oxidised finish. No high visibility
devices were attached to the powerlines, and nor were they required
to be.
Personnel information
The pilot was reported to have been fit, well and adequately
rested prior to the flight, and he was appropriately qualified and
endorsed for the agricultural operation in the helicopter.
Helicopter information
The investigation found that the helicopter was certified,
equipped, and maintained in accordance with existing regulations
and approved procedures. It was not, nor could it have been, fitted
with a wire-strike protection system, nor was there any regulatory
requirement for such a system.
No evidence was found of a defect in the helicopter or its
systems that may have influenced the circumstances of the
occurrence. The weight and balance of the helicopter were within
prescribed limits.
The helicopter's perspex windscreen was clean and there was no
pre-existing damage, or any obstruction that might have adversely
affected visibility from the cockpit. Based on the available
evidence, the aircraft was certified, equipped and maintained in
accordance with the regulations and approved procedures.
Meteorological information
No evidence was found to suggest that the weather or
environmental conditions influenced the circumstances of the
occurrence.
Wreckage and impact information
The powerline that was struck lay approximately perpendicular to
the helicopter's flightpath from the spray area to the
replenishment point (see Figure 1). The powerline was supported by
two poles, 669 m apart, which were located on heavily timbered
terrain. The point at which the powerline was severed by the
helicopter was estimated to be about 34 m above the tree tops, and
54 m above ground level.
Figure 1: Aerial view of powerline and approximate
aircraft track
The wreckage distribution and damage to the surrounding trees
was consistent with the helicopter impacting the ground with
significant vertical, but low forward speed.
A trail of shattered perspex commenced in a position
approximately underneath the point at which the powerlines had been
severed, and extended for approximately 180 m to the point where
the helicopter impacted the ground. The perspex corresponded to
that used in the construction of the helicopter windscreen. No
other helicopter components were found along the perspex trail.
The ground impact point and wreckage were located on steeply
sloping and heavily wooded terrain that was covered with dense
vegetation and large rocks (see Figure 2). The area was covered
with small to medium sized trees, some approximately 12 to 20 m
tall. The ground impact scars indicated that the helicopter was in
a relatively level attitude at the time of impact, before it slid
approximately 13 to 15 m down the sloping ground and collided with
a tree.
Figure 2: Helicopter wreckage
Impact damage to the helicopter was extensive. The helicopter
lay on its deformed left side with the cockpit left side panel, the
firewall, and the seat assembly compressed in a rearward/inward
direction. Damage to the cockpit right side panel was less severe
and the panel had retained its shape. A limited amount of the
shattered perspex windscreen remained with the main wreckage.
There was severe disruption to the cockpit, and the instrument
pedestal had been partially severed from the floor and was pushed
towards the pilot's seat. The engine, fuel, hydraulic, and flight
control systems' components were dislodged from their installed
position and damaged, but remained in their respective locations.
The engine was recovered from the accident site and transported to
an overhaul facility for technical examination under Australian
Transport Safety Bureau (ATSB) supervision. The examination
revealed that the engine was capable of normal operation at the
time of the accident.
The main rotor blades and mast, main transmission, and the
remainder of the helicopter's major components, systems, and
controls were also accounted for at the accident site, and in close
proximity to the main helicopter wreckage.
Both fuel tanks and their respective firewalls dislodged from
their installed position and were damaged. That included impact
puncture damage to the fuel tanks. While fuel leakage was evident
on the ground around the main wreckage, approximately 20 litres of
fuel was recovered from the helicopter's fuel tanks for sampling
purposes. A fuel sample was also taken from the re-fuelling truck.
The results of independent laboratory tests of both samples were
consistent and indicated that the Jet Fuel was bright, free from
water and considered suitable for use.
The remains of the tail boom structure was bent slightly
upwards, and the tail boom assembly had detached from the rear of
the centre fuselage frame about 2 m back from that frame. Sections
of the tail boom and the tail rotor drive shaft had separated at
impact, but remained oriented in the correct position relative to
each other. That was consistent with the helicopter having
negligible yaw at impact. A small section of the tail boom
structure was located down slope from the main helicopter
wreckage.
All major components and extremities of the installed
agricultural spray equipment were accounted for with the main
helicopter wreckage.
The left and right cockpit door frames were deformed just above
the upper door hinge, corresponding to about 15 to 20 cm above the
top of the instrument pedestal. That included a deep, circular
indentation to the right door frame and a partial tear and bulging
of the left door frame. The indentation in the right door frame was
'married' to a length of the severed power cables, and the damage
was found to be consistent with the cables having impacted with
that door frame (see Figure 3). There were no similar deformations
or markings to the instrument pedestal, cyclic or other helicopter
controls, or any other part of the helicopter.
Figure 3: The cut into the perspex bubble frame matched
with the conductor
Medical and pathological information
Based on the autopsy, toxicology, and medical reports, there was
no evidence to indicate that the pilot's performance was degraded
by physiological factors.
Survival aspects
A four-point restraint harness, with inertia reel shoulder
straps was fitted to the pilot's seat. Video footage of the
helicopter departing on the accident flight revealed that the pilot
had fastened the harness. Examination of the harness at the
accident site revealed that it remained attached to the firewall
and that there was no evidence of failure of the locking
mechanism.
The pilot was wearing a helmet at the time of the occurrence.
That helmet exhibited significant impact damage, but remained
intact. The helmet visor was found in the raised position.
Agricultural spray computer disk
The hard disk unit from the on-board agricultural spraying
computer was recovered. The unit was assessed by the manufacturer's
distributor and an external independent forensic expert. Those
examinations confirmed that the damage to the unit precluded
extraction of the data.
Organisation
Company Operations Manual
Section A19.5 of the company Operations Manual (manual)
contained the en-route procedures affecting low flying operations
by company pilots. In part, those procedures included that:
…due consideration shall be given to the dangers of unseen
wires, effects of turbulence and other low flying hazards. Prior to
the commencement of low level operations, the pilot in command
shall carry out an aerial survey of the area to establish an
optimum path and aircraft manoeuvring plan for the safe conduct of
the operation.
An overview of those procedures affecting the conduct of aerial
agricultural operations by company pilots was included at Section D
6.1 of the manual. That included that:
Normal aircraft operating procedures are detailed in the
relevant Pilot Operating Handbooks, the Aeronautical Information
Publication, as well as CAO 20.21, and the Agricultural Pilots
Manual (AAAA [Aerial Agricultural Association of Australia Limited]
Pilot and Operations Manual). And these should be followed unless
specified otherwise below.
Section D 6.5 of the manual reinforced the regulated requirement
for an agricultural pilot to conduct an aerial inspection of a
proposed treatment area prior to commencing aerial agricultural as
follows:
It is a CASA requirement that prior to commencing agricultural
operations the pilot shall carry out an aerial inspection of the
proposed treatment area - where practicable, a ground inspection
will also be conducted as per sub-section D 6.4.
The manual continued that the pre-treatment aerial inspection
was to include the examination of:
…Wires - their location in relation to the boundaries of the
area to be treated, height and position of, and distance between
poles and guy wires…
Additional information
Previous wirestrike occurrences
A review of the ATSB's accident and incident database revealed
that there were six single-fatality agricultural helicopter
accidents in Australia during the period 1 January 1995 to 20 June
2005. Those accidents represented 43% of all fatal helicopter
wirestrike accidents during the period.
Regulatory framework
Civil Aviation Regulation (CAR) 206 lists agricultural
operations as operations conducted for aerial work purposes.
Agricultural operations are defined as:
…the broadcasting of chemicals, seeds, fertilizers and other
substances from aircraft for agricultural purposes of pest and
disease control.
Civil Aviation Order (CAO) 40.6 defines the requirements of the
Agricultural Pilot Rating Grades 1 and 2. Those requirements
include completion of a period of ground training and a written
exam, before carrying out initial and operational flying training.
The operational flying training includes operational planning, such
as: ground and aerial inspections of the treatment area; assessment
of wires; and route selection to and from the treatment area,
including the height to fly during such transit flights. That
training is to be followed by a period under supervision, before
the newly rated agricultural pilot is able to conduct unrestricted
agricultural operations.
Aerial Application Pilots Manual3
Chapter 5 of the Aerial Application Pilots Manual contains
information pertaining to the identification of powerlines and
other low flying hazards with the potential to affect agricultural
operations. Chapter 8 of that manual outlines the information
specific to helicopter agricultural operations. Those chapters
elaborate on the recommended pre-flight planning and inspections
that should be carried out by a pilot prior to the conduct of
agricultural operations, including that:
If the pilot is obliged to rely on a farmer briefing regarding
wire hazards, a thorough interrogation of the farmer is necessary
to establish the position of concealed wires…They are seldom aware that wires outside the treatment area can
be hazardous to aircraft approaching for a spraying run. Farmers
may forget that they recently connected a shed to the power, ran a
new overhead wire to a pump or accidentally hooked a powerline with
a farm implement and pulled it over 'a bit'.Considerable effort is needed to extract vital information from
the client. Remember there are some wires that you may strike
unless the farmer makes you aware of their location.In addition, sometimes the background to the wires - trees,
hills etc. - provides a poor contrast, while poles may be concealed
by intervening obstacles or by being located so far to the
periphery of the pilot's visual field that they are not
noticed.During climb and cruise to and from the treatment area the
aircraft should track as directly as possible consistent with
avoiding nuisance areas and poor terrain.Don't come below possible powerline height until you are certain
all wires have been safely identified.
The property manager reported that he was aware of the
powerlines that were struck by the helicopter, but that he had not
passed that knowledge on to the pilot because they were located
outside both the area to be treated, and the safe transit route
between the replenishment truck and the proposed spray area.
Risk management
Australian/New Zealand Standard AS/NZS 4360:2004 Risk
Management (the Standard) defined risk as:
the chance of something happening that will have an impact upon
objectives.
NOTE 1: A risk is often specified in terms of an event or
circumstance and the consequences that may flow from it.
NOTE 2: Risk is measured in terms of a combination of the
consequences of an event … and their likelihood…
NOTE 3: Risk may have a positive or negative impact.
The Standard described risk management as 'the culture,
processes and structures that are directed towards realizing
potential opportunities, while managing adverse [or negative]
effects'. The risk management method described by the Standard
includes that initially the basic parameters or context affecting
the assessment of risk should be identified. That can include
'defining the extent of the project activity or function in terms
of time and location'. Residual risk is that 'risk remaining after
implementation of risk treatment'. Options for modifying or
treating identified risks with negative outcomes included:
- influencing the likelihood of a risk, in order to reduce the
probability of a negative outcome - changing the consequence(s) of an event to minimise the extent
of any losses.
Detection of powerlines
The requirements for the mapping and marking of power cables and
their supporting structures are published in Australian Standards
AS 3891.1 1991 Part 1: Permanent marking of overhead cables and
their supporting structures, and AS 3891.2 - 1992 Part 2: Marking
of overhead cables for low level flying. The general requirements
of those standards were discussed in ATSB
investigation report 200404286 and include that, in general,
there is no requirement for the marking of power cables with a
height above terrain, or obstacles of less than 90 m. The power
cable that was struck by the helicopter did not require marking in
accordance with either standard.
Technical committees are formed by Standards Australia to
develop and review relevant standards, and comprise a balance of
interested and affected parties that are nominated by generally
national organisations. The aim is that the standards should
include consideration of the views of large, common interest
groups. Organisations that consider they represent a valid,
previously unrepresented interest group are able to nominate for
consideration for inclusion in a committee.
A number of aviation industry associations and other bodies were
involved in the development of the Australian Standards affecting
the marking of overhead power cables and their supporting
structures. That did not include some of the groups and
associations normally associated with a number of agricultural and
other low-level operations.
There are currently a number of engineering solutions available,
with the potential to assist pilots identify overhead powerlines.
While their suitability or cost-effectiveness may not prove
acceptable for all helicopter types or operations, those
engineering solutions include, but are not limited to:
- laser-based systems that alert a pilot of approaching
electrified powerlines, or that scan the environment for wires and
other obstacles - enhanced ground proximity-based warning systems that include
relevant software and an onboard powerline database in order to
identify approaching powerlines.
1 Only those
investigation areas identified by the headings and subheadings were
considered to be relevant to the circumstances of the
occurrence.
2 The designation
'Soloy' indicates that the helicopter had been modified and fitted
with a turboshaft engine.
3 Version 6 prepared by
the AAAA. A significant upgrade of the Aerial Application Pilots
Manual was sponsored by the Civil Aviation Safety Authority
(CASA).