Bell Helicopter Co 206B (II), VH-PHF

The KAflex shaft had been fitted in accordance with the
published requirements in the supplemental type certificate (STC)
about 6 years, or 4,112.35 flying hours, prior to the occurrence.
As far as could be determined, no certifications had been made that
the shaft had been inspected in accordance with the STC inspection
requirements during that period.

There was no flight manual supplement supplied as part of the
STC, which would have alerted pilots to the specific inspection
requirements and the significance of red dust production. As well
as the daily inspection requirements for the shaft, the supplement
did not include the warning not to disturb the bolts and to reject
a shaft that showed evidence of turning of the fasteners.

The STC documents supplied with the shaft were not kept with the
current helicopter logbook, although it was readily available. The
retention of the STC documents in the archived logbook, instead of
the current logbook, meant that the STC inspection requirements
were overlooked and consequently not actioned by maintenance
personnel. That resulted in the STC inspection requirements not
being included as part of the routine or scheduled maintenance
paperwork packages when they were assembled for release to service
maintenance events.

The historical service record card for the shaft could not be
located and had not been included in the helicopter records as
required by the manufacturer in the STC accomplishment
instructions. The minimal reference made to the card in the STC
could easily have lead to the card being overlooked. When an
example of the card was obtained, the appropriate location for the
certification of maintenance activities was not readily apparent.
The lack of a specific area on the card to certify completion of
maintenance may have also contributed to the non-use of the card by
maintenance personnel, including the 1500-hourly inspection
certification in the airframe logbook. Also, inclusion of these
inspection certifications in the airframe logbook could lead to the
certification history for a driveshaft being lost if a driveshaft
was subsequently moved from one helicopter to another. When
overhaul became due, this service history would also have been
unavailable to the manufacturer when the shaft and accompanying
historical service card were returned to them.

The shaft failure had been initiated by fretting type movement
at a flex frame bolted joint. This progressed until the joint
failed, resulting in the gross overload failure of the remaining
frames. That movement, in its early stages, should have been
detectable by the presence of the red dust or loose bolted joints
described in the STC inspection warnings. Had the maintenance and
operating personnel been aware of the STC inspection schedules,
they would have had a better understanding of the significance of
the red dust and its ramifications.

Although the operator submitted that his personnel would have
detected red dust had it been present around the flex frame joints,
the wear pattern evident on the flex frame joint in Figure 1 was
consistent with the flex frame fastener being loose for a period of
time prior to the failure. The loose bolted joints were not
detected. In this occurrence, the loss of bolted joint integrity
may have progressed past the point where dust production may
occur.

At 1702 central standard time on 14 June 2004, a Bell Helicopter
Company 206B(II) Jetranger, registered VH-PHF, was being operated
for a medical evacuation from Deep Well, NT, to Alice Springs.
About 5 NM south-west of Alice Springs Airport, while cruising at
500 ft above ground level at 100 kts, the pilot felt a vibration
and heard a loud bang accompanied by a reduction in main rotor
torque. The pilot immediately placed the helicopter into an
autorotative descent and broadcast a MAYDAY¹ to the Alice Springs Air Traffic
Control aerodrome controller. The pilot landed the helicopter in a
clearing and the five occupants were uninjured.

Initial inspection of the helicopter by the operator revealed
that the KAflex²
driveshaft between the engine free-wheeling unit and the main
transmission had failed. The failed shaft and its components were
removed from the helicopter and forwarded to the Australian
Transport Safety Bureau (ATSB) for metallurgical examination. The
examination found that the failures had occurred in the arms of the
web elements, with all of the fractures typical of gross-overload
failure from either a single or small number of cycles. Of
significant interest was the separation of one of the flex frame
unions (see Figure 1). This section showed evidence of wear and
deformation consistent with looseness of the bolted joint fastener.
Fatigue cracking had initiated from the bore or worn surfaces of
the frame and propagated radially away from the hole, intersecting
the side of the frame and freeing the connection.

Figure 1: Worn fastener bore and fracture in
flex frame. Arrows indicate the point

of fatigue crack initiation and the direction of propagation.

Maintenance history

The helicopter's Maintenance Release was valid until 27 November
2004 or 12,351.80 hours in service, whichever occurred first. At
the time of the failure, the helicopter had 12,168.25 hours in
service. The operator had responsibility for the maintenance of the
helicopter, which was conducted under a valid Certificate of
Approval. The helicopter was operated in the Normal category, Day
VFR.

The helicopter was maintained as a Class B type aircraft, with
the airframe maintenance conducted in accordance with the
manufacturer's prescribed maintenance procedures. In this instance,
the Bell Helicopter Textron Company 206 Maintenance Manual
BHT-206A/B-SERIES-MM-1 was identified in the Logbook Statement as
the primary documentation. However, the driveshaft manufacturer's
documentation was not identified as required supplemental
documentation in that statement. The inspection schedule worksheets
for maintenance were copied, for use by the maintenance personnel,
directly from the airframe manufacturer's manuals. No supplemental
maintenance inspection sheets were incorporated into any of the
maintenance worksheet packages that specifically identified
maintenance actions to be performed for the KAflex driveshaft.

The helicopter underwent a 300-hourly inspection for the issue
of a maintenance release at Moorabbin, Victoria on 27 November
2003. No entries were recorded on the maintenance release with
regard to any daily or periodic inspection requirements specific to
the KAflex driveshaft.

Main driveshaft

The Jetranger was delivered with a proprietary designed main
driveshaft. The driveshaft, which comprised a spherical coupling at
either end of a torque shaft, was designed to transmit power from
the engine freewheeling unit output adapter to the main
transmission input quill. The engine's output shaft speed was
around 6,000 RPM³
during helicopter operation. The application of power and flight
and ground loads all contributed to drive line misalignment during
operation. The spherical coupling design compensated for that
misalignment under normal operating conditions. The main driveshaft
was subject to ongoing monitoring through heat sensitive
temperature indicators that detected overheating caused by
inadequate lubrication, wear, or excessive misalignment of the
drive train elements. Periodic maintenance of the driveshaft
included disassembly, inspection and lubrication in accordance with
the Bell Helicopter Textron Company 206 Maintenance Manual, to
ensure the continuing airworthiness of the driveshaft.

On 19 January 1998, at 8,055.9 hours aircraft total time in
service, the Bell manufactured engine-to-transmission driveshaft in
the helicopter had been replaced with a KAflex unit. The new
driveshaft was designed to replace the proprietary unit and had
been marketed as providing reduced maintenance, longer time between
overhauls, and greater reliability.

The Kamatics Corporation web page advised:

Helicopter flight manoeuvres generate high misalignment between
the engine and the transmission, which must be accommodated by the
connecting driveshaft. Such driveshafts, which rotate at speeds
over 6000 RPM, often incorporate grease lubrication and seals.
Designs of this type are susceptible to loss of lubrication, which
results in overheating and possible failure, a major safety
concern.

The KAflex driveshaft is a mechanical drive coupling which
requires no lubrication or seals, and transmits power while
accommodating high angular misalignment and length change through
the use of flexible rectangular frames. These frames are bolted
together at the corners in a truss-like arrangement, which are
attached to shaft end fittings to allow for drop-in installation in
the drive line. A fail-safe feature enables the coupling to
continue to transmit power even in the unlikely event of a failure
in a load carrying member.

KAflex driveshafts are custom designed for specific applications
and selected because they offer superior, maintenance-free
performance with extended 'on condition' service-life, resulting in
unequalled reliability, increased readiness and cost effectiveness.
They are supplied both as individual couplings and as complete
driveshafts.

The KAflex driveshaft had been fitted in accordance with
Kamatics Corporation supplemental type certificate (STC) SH 7767SW.
The helicopter was then ground run and test flown with no defects
found. While the KAflex driveshaft remained fitted to the
helicopter, the requirements of airworthiness directive (AD)/Bell
206/79 Amdt 1⁴ were
no longer applicable to the helicopter.

The STC documentation stipulated that, upon completion of the
modifications and installation of the shaft, the historical service
record was to be completed, applicable logbook entries made and the
card to be kept with the aircraft logbooks. At the completion of
its recommended time in service between overhauls, the shaft and
the completed historical service card would be returned to the
manufacturer for overhaul. While an entry in the helicopter's
logbook was made for the installation of the KAflex shaft into the
helicopter, no historical service record was found in the
helicopter's logbooks pertaining to the shaft.

Maintenance and inspection

A copy of the STC was kept with the archived helicopter logbooks
and worksheets, in a separate binder to the current helicopter
logbook binder. Both binders were located at the operator's main
office. The STC was available to the engineers maintaining the
helicopter, but it was not identified by them as a document that
they would need to refer to routinely in their maintenance
activities.

Although the STC and the manufacturer's website stated that the
driveshaft was 'maintenance free' Sections 3 and 4 of the STC
detailed the inspection and maintenance regime that the
manufacturer expected to be performed while the driveshaft was in
service. Section 3 of the STC detailed pre-flight, 100-hourly and
1,500-hourly inspections that were to be performed throughout the
6,000 hour service life⁵ of the shaft. The inspection advice
described examination of the flex frames for the production of 'red
dust' showing up as a red metallic residue. Section 3 also
contained requirements for a 6,000 hour inspection (which it
referred to as maintenance requiring return to the manufacturer)
and conditional inspections after specific events, such as an
overtorque, an overspeed, a sudden stoppage, a hard landing or a
lightning strike. Section 3 also contained the following bold type
warning with regard to flex frame attachment hardware:

WARNING

DO NOT disturb or tighten flex frame nuts or bolts. Evidence of
turning

fasteners by wrench or other means is cause for
rejection.

Section 4 of the STC listed maintenance requirements for the
driveshaft. That information stated that there was no periodic
maintenance requirement for the KAflex driveshaft.

The operator's managing director stated that at no time did any
of his personnel detect the production of red dust residue on the
shaft. He also advised that had there been red dust production
around the flex frame joints, his personnel would have detected it
and prevented the failure. The manufacturer stated that red dust is
usually produced in the initial stage of loss of integrity of the
bolted joints, but noted that this was not always the case and
operators should be vigilant with regard to inspection for loose
bolted joints.

From the time of installation of the shaft on 19 January 1998 to
the time of the occurrence on 14 June 2004, there were no entries
detailing the conduct of periodic or 1,500-hourly inspection
certification requirements of the KAflex driveshaft in the
helicopter's logbooks, or in the worksheets for maintenance for the
issue of a maintenance release. This represented the 4,112.35 hours
in service for the KAflex driveshaft. However, there was no
stipulation in the STC Section 3 instructions to require
certification for the completion of the inspections detailed in
that section.

There was also no amendment insert in the helicopter's flight
manual for the daily inspection as described in the STC, Section 3
- DAILY INSPECTION BEFORE FIRST FLIGHT OF THE DAY. There was also
no stipulation in the STC that the flight manual should be amended
in order to make that information readily available to the
pilot.

When interviewed, the pilot in command was asked to describe the
execution of a daily inspection of the helicopter. While a detailed
explanation was given to the interviewer, at no time was the
driveshaft manufacturer's warning caveat mentioned or alluded to by
the pilot. As this is a bold type warning in the manufacturer's
documentation, it should have been a recall item readily identified
during this discourse.

Historical service record

There was minimal reference made to the historical service
record in the STC. A copy of the card was obtained from the local
Australian distributor for KAflex. There was no provision on the
card for certification of the 100-hourly and 1,500-hourly
inspections. The historical service record card had not been
incorporated into the maintenance records for the helicopter as
required by the manufacturer in the accomplishment instructions of
the STC.

¹ International
radio broadcast for urgent assistance.

² A proprietary
name for a driveshaft manufactured by a Unites States company,
Kamatics Corporation.

³ Output shaft
speed at 100% main rotor RPM.

⁴ AD/Bell 206/79
Amdt 1 detailed the inspection and installation of a Visual Aid
Overheat Indicator on a Bell manufactured main input drive shaft
assembly. It was later cancelled as those requirements were
incorporated into the 100-hourly maintenance servicing
requirements.

⁵ At the time of
shaft installation, the STC stipulated a 4,000 hour service life.
Service Instruction 2348 Revision "E" dated September 1999 extended
this service life to 6,000 hours between overhauls.