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Insert document title
Location | Date
ATSB Transport Safety Report[Insert Mode] Occurrence
InvestigationXX-YYYY-####Final
Investigation
Examination of components from a GT ‘Kruza’ gyroplane –
Technical assistance provided to the Australian Sports Rotorcraft
Association
Investigation
near Mangalore Airport, Victoria | 14 January 2012
ATSB Transport Safety ReportAviation External
InvestigationAE-2012-013Final – 22 July 2013
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Released in accordance with section 25 of the Transport Safety
Investigation Act 2003
Publishing information
Published by: Australian Transport Safety Bureau Postal address:
PO Box 967, Civic Square ACT 2608 Office: 62 Northbourne Avenue
Canberra, Australian Capital Territory 2601 Telephone: 1800 020
616, from overseas +61 2 6257 4150 (24 hours) Accident and incident
notification: 1800 011 034 (24 hours) Facsimile: 02 6247 3117, from
overseas +61 2 6247 3117 Email: [email protected] Internet:
www.atsb.gov.au
© Commonwealth of Australia 2013
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Contents
The occurrence
........................................................................................................................1
Impact with terrain 1
Context
......................................................................................................................................3
Technical assistance 3 Flight control system 3 Examination of the
evidence 3
Rotor head components and torque tube 3 Garmin GPSmap 295 4
Blackberry mobile phone 4
Other gyroplanes 4
Analysis
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10 Torque tube failure 10
Summary
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11 Further information 11
General details
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12 Occurrence details 12 Aircraft details 12
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ATSB – AE-2012-013
The occurrence Impact with terrain On 14 January 2012 at
approximately 0930 (local time), a ‘GT Kruza’ gyroplane
(registration G-762) with a pilot and student passenger on-board,
departed Mangalore Aerodrome, Victoria, for a one hour training
flight. At around 1130 later that morning, a member of the public
identified the wreckage of the gyroplane, which had impacted
terrain a short distance from the aerodrome. Both occupants had
sustained fatal injuries. There were no witnesses to the
accident.
The Victorian Police Service was responsible for investigating
this accident; assisted by investigators from the Australian Sports
Rotorcraft Association (ASRA). From an assessment of the accident
site, ASRA investigators determined that the gyroplane had impacted
terrain at high speed with a near-vertical nose-down attitude. The
rotor system had detached from the airframe during the impact
sequence and lay several metres from the majority of the wreckage.
There was no evidence of fire.
A preliminary inspection of the gyroplane’s flight controls
found that the rotor head torque tube had fractured through the
central section where it adjoined the rotor head torque bar (Figure
1 and Figure 2). Upon closer examination, ASRA investigators
identified evidence of possible pre-existing cracking within the
torque bar at the point of failure, and in consideration of the
critical nature of this component in the flight control system,
ASRA staff sought assistance from the Australian Transport Safety
Bureau (ATSB) in the formal technical examination and analysis of
the torque bar failure. Assistance was also sought in the
examination and possible data recovery from a GPS unit and personal
mobile telephone being carried on board the gyroplane.
Figure 1: ‘GT Kruza’ gyroplane, registration G-762, prior to the
accident. The location of
the rotor head and torque tube is arrowed.
Source: Australian Sports Rotorcraft Association
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ATSB – AE-2012-013
Figure 2: The fractured torque tube as found at the accident
site.
Source: Australian Sports Rotorcraft Association
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ATSB – AE-2012-013
Context Technical assistance A number of items were recovered
from the gyroplane and submitted to the Australian Transport Safety
Bureau (ATSB) with a request from ASRA to conduct additional
examinations. Submitted items included components from the flight
controls of the gyroplane; the fractured torque tube and the
majority of the rotor head. Two electronic devices were also
submitted; a Garmin ‘GPSmap 295’ and a Blackberry mobile phone.
In order to facilitate the ATSB’s technical investigation and to
provide protection to the analysis findings and any electronic data
recovered, an External Investigation was commenced in accordance
with the provisions of the Transport Safety Investigation Act
2003.
Flight control system Pitch and bank control of the gyroplane
was effected through pilot manipulation of the control column.
Forward-rearward and side-to-side movement of the column produced a
corresponding movement of the rotor head – tilting the plane of the
rotor disk. Control rods were connected to the rotor head of the
gyroplane through the 3/4-inch (19 mm) diameter torque tube, which
was bolted and clamped to the torque bar (Figure 3 and Figure
4).
A 1/4-inch (6.3 mm) diameter pinch bolt was inserted through
both the torque tube and torque bar and then tightened against a
nylon-insert locking nut - the intention being to rigidly clamp
both items together during operation. A hole through the torque
tube accommodated the pinch bolt. The nature of the torque bar and
tube assembly design represented a critical link in the flight
control system of the gyroplane, with any separation of the
components likely resulting in a loss of control.
Examination of the evidence Rotor head components and torque
tube As received, the torque tube had fractured transversely into
equal halves through the central bolt hole. Indications of surface
fretting and wear were present on the clamping surfaces of the
torque tube and bore of the torque bar - providing evidence of
relative movement between the torque tube and bar during service
(Figure 5).
Examination of the torque tube fracture surfaces using a
binocular microscope confirmed the presence of progressive crack
growth features on the entirety of the fracture surface. Repeated,
concentric crack progression marks were indicative of a fatigue
cracking mechanism, with origin at the external corners of the
uppermost torque tube hole (through which the pinch bolt passed).
The cracking had extended circumferentially around the tube
diameter to the point where the cracks met the lower bolt hole and
the tube fractured (Figure 7 to Figure 9).
Externally, the pinch bolt nut flanks showed paint loss
consistent with the security of the nut having been checked prior
to receipt by the ATSB (possibly during routine maintenance). A
purple coloured ‘torque stripe’ across the nut/bolt end showed no
evidence of movement or loosening between the two components
(Figure 6).
Chemistry and hardness
Information from the gyroplane manufacturer indicated that the
torque tube was specified to have been produced from a thin-walled
(~1.5 mm), 3/4-inch diameter 4130 medium-carbon, low alloy steel
tube. To verify, a section of the tube was removed and examined
under the scanning electron microscope, which, under
semi-quantitative analysis, showed the steel to be alloyed
predominantly with chromium and manganese with minor additions of
molybdenum – consistent
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ATSB – AE-2012-013
with the 4130 specification. The measured hardness of the tube
(266 HV0.5) was consistent with the 4130 alloy steel in the
quenched and tempered condition.
Garmin GPSmap 295 The Garmin GPSMAP 295 was a portable GPS
navigation device capable of storing flight path information.
As-received, the outer casing of the device was severely deformed
(Figure 10). The device was decontaminated and then disassembled to
view the condition of the internal circuitry.
The circuit board was deformed and cracked in several locations.
The EMI shield was removed from the circuit board and multiple
electronic chips were found to have detached from the circuit board
under the influence of the accident impact loads (Figure 11).
While the discrete memory chip which contained the most recent
flight path information was identified, it had sustained damage to
several of its ball-grid array connection pads. A local solder
repair of the electronic connection between the memory chip and the
circuit board pad was attempted; however no valid data was able to
be recovered.
Blackberry mobile phone Smart-phone devices, such as the
BlackBerry unit recovered from the accident site, contain
componentry and functionality to enable display and recording of
positional and track information when running dedicated
applications for this purpose. Due to the level of in-built
encryption in this class of device however, and in the absence of a
specific password for the unit, data recovery was not possible.
Other gyroplanes The manufacturer of the gyroplane reported to
ASRA investigators that only one other of their aircraft had been
manufactured with the same rotor head and torque tube design as
G-762. Immediately after this accident, the control system for that
gyroplane was removed from service, disassembled and the torque
tube examined. No evidence of cracking was found.
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ATSB – AE-2012-013
Figure 3: Close view of the rotor head taken during construction
of the Kruza G-762
prior to final painting. Several key components are
labelled.
Source: Australian Sports Rotorcraft Association
Figure 4: Rotor head and fractured torque tube from G-762, as
received by the ATSB.
Source: ATSB
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ATSB – AE-2012-013
Figure 5: Fractured torque tube showing the point of failure
intersecting a central bolt hole. The darkened areas on the tube
surface are fretting damage from relative movement between the
torque tube and torque bar.
Source: ATSB
Figure 6: Torque bar clamping arrangement. The purple ‘torque
stripe’ was intact on the pinch bolt which indicated that the bolt
had not been adjusted since the initial installation. Paint loss on
the nut flanks was indicative that the pinch bolt may have been
checked for security during routine maintenance.
Source: ATSB
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ATSB – AE-2012-013
Figure 7: Fracture surface of the failed torque tube. Flashing
from drilling the central hole remains in place.
Source: ATSB
Figure 8: Evidence of crack progression and ‘beach marks’ on the
fracture surface confirms that the torque tube failed by
fatigue.
Source: ATSB
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ATSB – AE-2012-013
Figure 9: Evidence of crack progression and ‘beach marks’ on the
fracture surface confirms that the torque tube failed by
fatigue.
Source: ATSB
Figure 10: A Garmin GPSmap 295 and a Blackberry mobile phone
device were recovered from the accident and submitted to the ATSB
with a request from ASRA to recover the data. The units are shown
in the as-received condition.
Source: ATSB
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ATSB – AE-2012-013
Figure 11: Internal circuit board of the GPSmap 295 showing the
displaced memory chips.
Source: ATSB
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ATSB – AE-2012-013
Analysis Torque tube failure Failure of the rotor head torque
tube occurred as a result of a progressive fatigue cracking
mechanism, initiated at the internal corners of a through-drilled
hole for the assembly clamping bolt. The manifestation of fatigue
cracking in this region was a direct result of the development of
dynamic (operational) bending stresses within the component, to
levels that exceeded the fatigue endurance of the tube
material.
The design of the torque bar and tube unit provided for the
translation of control system loads into cantilever bending loads
at the junction between the bar and tube. By virtue of the rigidity
differences between the hollow-section tube and solid bar, bending
load concentration within the tube would be expected at the tube
entry into the torque bar, with further amplification arising
should movement within the assembly occur as a function of
inadequate clamping. Local stress-raising features in loaded areas
can also significantly increase the predisposition to fatigue
cracking – in this instance, the placement and production of the
pinch bolt hole can be shown to have significantly concentrated the
stresses at the hole corners – making those regions ideal fatigue
crack initiation sites.
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ATSB – AE-2012-013
Summary The Australian Sports Rotorcraft Association (ASRA)
requested the Australian Transport Safety Bureau (ATSB) to provide
technical assistance in the examination of items recovered from the
wreckage of a GT ‘Kruza’ gyroplane that collided with terrain near
Mangalore Aerodrome, Victoria on 14 January 2012. The following
conclusions were drawn from the examinations performed:
• Fracture of the rotor head torque tube was directly associated
with the development of fatigue cracking that had initiated from
stress concentration effects around a clamping bolt hole that
passed, by design, through the centre of the tube.
• The level of surface fretting and evidence of movement between
the tube and torque bar suggested a level of inadequate clamping
force between the components.
• There was no evidence of loosening of the clamping bolt
locking nut.
• There was some evidence to suggest that the tightness/security
of the clamping bolt nut had been checked at some time before the
accident.
• No data was able to be recovered from either the Blackberry
mobile phone or the Garmin GPSmap 295 device.
Further information The investigation into the circumstances of
this accident was conducted by the Victorian Police Service,
supported by the Australian Sports Rotorcraft Association. The
involvement of the Australian Transport Safety Bureau was limited
to the technical examinations summarised within this report.
Requests for further information regarding the occurrence should be
directed to the Victorian Police Service or ASRA.
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ATSB – AE-2012-013
General details Occurrence details
Date and time: 14 January 2012
Occurrence category: Accident
Primary occurrence type: Loss of control leading to impact with
terrain
Location: Near Mangalore Aerodrome, Victoria
Aircraft details Manufacturer and model: GT Gyroplanes
‘Kruza’
Registration: G-762
Total time in service 310.9 hours
Engine model Subaru EJ25
Type of operation: Flying training
Persons on board: Crew – 1 Passengers – 1
Injuries (fatal): Crew – 1 Passengers – 1
Damage: Destroyed
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AT
SB
Transp
ort S
afety Rep
ort
Aviation E
xternal Investigation
Exam
ination of components from
a GT ‘K
ruza’ gyroplane – Technical assistance provided to the A
ustralian Sports
Rotorcraft A
ssociation
AE
-2012-013 Final – 22 July 2013
Investigatio
n
Australian Transport Safety Bureau
24 Hours 1800 020 616 Web www.atsb.gov.auTwitter @ATSBinfoEmail
[email protected]
Examination of components from aGT ‘Kruza’ gyroplane –Technical
assistance provided to theAustralian Sports Rotorcraft
Associationnear Mangalore Airport, Victoria | 14 January 2012The
occurrenceContextTechnical assistanceFlight control
systemExamination of the evidenceOther gyroplanes
AnalysisTorque tube failure
SummaryFurther information
General detailsOccurrence detailsAircraft details