Sikkerhetstilråding
Sikkerhetstilråding SL nr.
2018/01T
The failure mode, i.e. crack
formation subsurface with limited spalling initiated from a surface damage,
observed in the LN-OJF accident is currently not fully understood. The
investigation has shown that the combination of material properties, surface treatment,
design, operational loading environment and debris gave rise to a failure mode
that was not previously anticipated or assessed.
The Accident Investigation Board
Norway recommends that the European Aviation Safety Agency (EASA) commission
research into crack development in high-loaded case-hardened bearings in
aircraft applications. An aim of the research should be the prediction of the
reduction in service-life and fatigue strength as a consequence of small
surface damage such as micro-pits, wear marks and roughness.
Sikkerhetstilråding SL nr.
2018/02T
The MGB, which was later
installed in LN-OJF, fell off a truck during transport. It was inspected,
repaired and released for flight by Airbus Helicopters without detailed
analysis of the potential effects on the critical characteristics of the MGB.
The current regulatory framework for large rotorcraft does not make connections
between the Instructions for Continued Airworthiness (ICA) and requirements for
critical parts subject to an unusual event.
The Accident Investigation Board
Norway recommends that the European Aviation Safety Agency (EASA) assess the
need to amend the regulatory requirements with regard to procedures or
Instructions for Continued Airworthiness (ICA) for critical parts on helicopters
to maintain the design integrity after being subjected to any unusual event.
Sikkerhetstilråding SL nr.
2018/03T
Rolling contact fatigue as
observed in the LN-OJF accident was not considered during type certification,
neither is it directly addressed in the current certification specifications.
The Accident Investigation Board
Norway recommends that European Aviation Safety Agency (EASA) amend the
Acceptable Means of Compliance (AMC) to the Certification Specifications for
Large Rotorcraft (CS-29) in order to highlight the importance of different
modes of component structural degradation and how these can affect crack
initiation and propagation and hence fatigue life.
Sikkerhetstilråding SL nr.
2018/04T
The chip detection system fitted
to LN-OJF did not produce any warnings of the impending planet gear
catastrophic failure, and the potential of detection was limited. The
Certification Specifications for Large Rotorcraft (CS-29) do not specify the
chip detection system’s functionality and performance.
The Accident Investigation Board
Norway recommends that the European Aviation Safety Agency (EASA) revise the
Certification Specifications for Large Rotorcraft (CS-29) to introduce
requirements for MGB chip detection system performance.
Sikkerhetstilråding SL nr.
2018/05T
The LN-OJF accident was a result
of a fatigue fracture in one of the eight second stage planet gears in the
epicyclic module of the MGB, a critical part in which cracks developed
subsurface to a catastrophic failure without being detected. It might not be
possible to assess the fatigue reliability of internal MGB components, or
design a warning system that works with sufficient efficiency and warning time,
thus the MGB should be designed fail-safe.
The Accident Investigation Board
Norway recommends that the European Aviation Safety Agency (EASA) develop MGB
certification specifications for large rotorcraft to introduce a design
requirement that no failure of internal MGB components should lead to a
catastrophic failure.
Sikkerhetstilråding SL nr. 2018/06T
The investigation into the
accident to LN-OJF has revealed that the tests performed during the design and
certification of the Airbus Helicopters EC 225 LP were in accordance with
applicable regulations. However, with regard to the risks associated with
offshore operations, there is a less stringent continued operational
reliability test requirement for large rotorcraft compared with the Extended
Operations and All Weather Operations regime for fixed wing aircraft.
The Accident Investigation Board
Norway recommends that the European Aviation Safety Agency (EASA) develop
regulations for engine and helicopter operational reliability systems, which
could be applied to helicopters which carry out offshore and similar operations
to improve safety outcomes.
Sikkerhetstilråding SL nr.
2018/07T
The investigation into the
accident to LN-OJF has revealed that the tests performed during the design and
certification of the Airbus Helicopters EC 225 LP were in accordance with
applicable regulations. However, with regard to the risks associated with
offshore operations, there is a less stringent continued operational
reliability test requirement for large rotorcraft compared with the Extended
Operations and All Weather Operations regime for fixed wing aircraft.
The Accident Investigation Board
Norway recommends that the European Aviation Safety Agency (EASA) develop
regulations for engine and helicopter operational reliability systems, which
could be applied to helicopters which carry out offshore and similar operations
to improve safety outcomes.
Sikkerhetstilråding SL nr.
2018/08T
The investigation into the
accident to LN-OJF has found that only a few second stage planet gears in
Airbus Helicopters EC 225 LP and AS 332 L2 ever reached their intended
operational time limit before being rejected during overhaul inspections or
non-scheduled MGB removals.
The Accident Investigation Board
Norway recommends that the European Aviation Safety Agency (EASA) review and
improve the existing provisions and procedures applicable to critical parts on
helicopters in order to ensure design assumptions are correct throughout its
service life.
Sikkerhetstilråding SL nr.
2018/09T
The investigation into the
accident to LN-OJF has found that only a few second stage planet gears in
Airbus Helicopters EC 225 LP and AS 332 L2 ever reached their intended
operational time limit before being rejected during overhaul inspections or
non-scheduled MGB removals.
The Accident Investigation Board
Norway recommends that the European Aviation Safety Agency (EASA) review and
improve the existing provisions and procedures applicable to critical parts on
helicopters in order to ensure design assumptions are correct throughout its
service life.
Sikkerhetstilråding SL nr.
2018/10T
During the investigation into
the accident to LN-OJF, considerable time and resources by the AIBN has been
drawn to request, wait for release acceptance and review of design and
certification documents.
The Accident Investigation Board
Norway recommends that the European Commission (DG MOVE) in collaboration with
European Aviation Safety Agency (EASA) evaluates the means for ensuring that
investigation authorities have effectively free access to any relevant
information or records held by the owner, the certificate holder of the type
design, the responsible maintenance organisation, the training organisation,
the operator or the manufacturer of the aircraft, the authorities responsible
for civil aviation, EASA, ANSPs and airport operators.
Sikkerhetstilråding SL nr.
2018/11T
During the investigation into
the accident to LN-OJF, considerable time and resources by the AIBN has been
drawn to request, wait for release acceptance and review of design and certification
documents. ICAO Annex 13 Chapter 5.12 does not refer explicitly to the
protection of sensitive proprietary information regarding design and
certification.
The Accident Investigation Board
Norway recommends that the International Civil Aviation Organisation (ICAO)
evaluates the means for ensuring that investigation authorities have
effectively free access to any relevant information or records held by the
owner, the certificate holder of the type design, the responsible maintenance
organisation, the training organisation, the operator or the manufacturer of
the aircraft, the authorities responsible for civil aviation, certification
authorities, ANSPs and airport operators.
Sikkerhetstilråding SL nr.
2018/12T
The LN-OJF accident was a result
of a fatigue fracture in one of the eight second stage planet gears in the
epicyclic module of the MGB, a critical part in which cracks developed
subsurface to a catastrophic failure without being detected. With the knowledge
from this investigation, all effort should lead to a robust design in which a
single load path should demonstrate compliance to CS 29.601(a), 29.602 and
29.571 without compromising its structural integrity and not only by depending
on detection systems or maintenance checks.
The Accident Investigation Board
Norway recommends that Airbus Helicopters revise the type design to improve the
robustness, reliability and safety of the main gearbox in AS 332 L2 and EC 225
LP.
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