Safety recommendation SL No 2018/15T

22 August 2017, LN-PTS crashed near Holmestrand. In connection with weighing of aircrafts, it exists a requirement of a new weighing if the empty mass has been changed more than +/- 0,5 % of maximum landing mass and/or CG has been changed more than +/- 0,5 % of MAC. Furthermore, it is normally a requirement to do an assessment of the new values with the values from previous weighing. The Accident Investigation Board Norway (AIBN) consider that a form for empty weight and balance should consist of an assessment of the new values with the values from previous weighing. In this case, the airplane’s empty weight and corresponding center of gravity values were not used to make mass and balance calculations. Several studies suggest that general pilots have a relaxed attitude towards these limitations.

The Accident Investigation Board Norway (AIBN) recommends that the Civil Aviation Authority Norway should provide appropriate “Safety promotion” information. From an airworthiness point of view, measures should be taken to make probability assessments of new values in connection with weighing. Furthermore, information should be provided on the importance of flight operation personnel complying with the limitations announced in the aircraft’s manuals.

Safety recommendation SL No. 2016/01T

Cracks in the exhaust silencer of Alexander Schleicher GmbH & Co Segelflugzeugbau ASK 21 Mi aircraft can cause heat damage and possible fire in the engine compartment. In the opinion of the Accident Investigation Board Norway, this has not been sufficiently covered and emphasised in the aircraft's flight manual, maintenance programme or other official information from the glider manufacturer.

The Accident Investigation Board Norway therefore recommends that Alexander Schleicher GmbH & Co Segelflugzeugbau makes public relevant information so that users of ASK 21 Mi can be advised on how to detect leaks in the exhaust silencer at an early stage.

Safety recommendation SL No. 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.

Safety recommendation SL No. 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.

Safety recommendation SL No. 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.

Safety recommendation SL No. 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.

Safety recommendation SL No. 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.

Safety recommendation SL No. 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.

Safety recommendation SL No. 2018/07T

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 before being rejected during overhaul inspections or non-scheduled MGB removals. The parts rejected against predefined maintenance criteria were not routinely examined and analysed by Airbus Helicopters.

The Accident Investigation Board Norway recommends that European Aviation Safety Agency (EASA) make sure that helicopter manufacturers review their Continuing Airworthiness Programme to ensure that critical components, which are found to be beyond serviceable limits, are examined so that the full nature of any damage and its effect on continued airworthiness is understood, either resulting in changes to the maintenance programme, or design as necessary, or driving a mitigation plan to prevent or minimise such damage in the future.

Safety recommendation SL No. 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.

Safety recommendation SL No. 2018/09T

The investigation into the accident to LN-OJF has demonstrated that a critical structural component could fail totally without any pre-detection by the existing monitoring means.

The Accident Investigation Board Norway recommends that the European Aviation Safety Agency (EASA) research methods for improving the detection of component degradation in helicopter epicyclic planet gear bearings.

Safety recommendation SL No. 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.

Safety recommendation SL No. 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.

Safety recommendation SL No. 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.

Safety recommendation SL no 2015/07T

The loss of engine power was presented to the pilot on CWP with yellow GOV light. According to the helicopter’s emergency checklist, the action to be taken is: “LAND AS SOON AS PRACTICABLE”. AIBN is of the opinion that this does not reflect the need for immediate reaction from the pilot in the event of a fuel pressure break and subsequent loss of engine power.

The Accident Investigation Board Norway therefore recommends that Turbomeca consider changes to the AS 350 B3e warning system and other helicopter types in the Airbus family with similar warning logic, so that the pilot receives the correct information in relation to the severity of the occurred failure. (A similar safety recommendation is also issued to Airbus Helicopters.)

Safety recommendation SL no 2015/08T

The loss of engine power was presented to the pilot on CWP with yellow GOV light. According to the helicopter's emergency checklist, the action to be taken is: “LAND AS SOON AS PRACTICABLE”. AIBN is of the opinion that this does not reflect the need for immediate reaction from the pilot in the event of a fuel pressure break and subsequent loss of engine power.

The Accident Investigation Board Norway therefore recommends that Airbus Helicopters consider changes to the AS 350 B3e warning system and other helicopter types in the Airbus family with similar warning logic, so that the pilot receives the correct information in relation to the severity of the occurred failure. (A similar safety recommendation is also issued to Turbomeca.)

Safety recommendation SL No 2018/13T

On 30 April 2016, the AS 350 B3, LN-OSG was subject to an uncontrolled landing which caused the main rotor blades to hit the ground and into the helicopter's tailboom. The engine continued to run after the free turbine had thrown its turbine blades. The turbine blades were thrown after the engine's reduction gearbox ruptured and the free turbine was decoupled and accelerated beyond the speed it was designed to withstand. The consequence of this was that hot exhaust gases escaped from the engine into the engine compartment and there was a fire.

The Accident Investigation Board Norway recommends Airbus Helicopters, in cooperation with Safran Helicopter Engines to study technical solutions for AS 350 helicopters equipped with Arriel 2 engines, as well as other Airbus helicopter types with similar Arriel engine installations. The purpose of this study should be to find ways of reducing the risk of fire following accidents where the free turbine blades have shedded.

Safety recommendation SL No 2018/14T

On 30 April 2016, the AS 350 B3, LN-OSG was subject to an uncontrolled landing which caused the main rotor blades to hit the ground and into the helicopter's tailboom. The engine continued to run after the free turbine had thrown its turbine blades. The turbine blades were thrown after the engine's reduction gearbox ruptured and the free turbine was decoupled and accelerated beyond the speed it was designed to withstand. The consequence of this was that hot exhaust gases escaped from the engine into the engine compartment and there was a fire.

The Accident Investigation Board Norway recommends that EASA study the opportunity to mandate the solutions developed by Airbus Helicopters in cooperation with Safran Helicopter Engines.

Safety recommendation SL no 2019/02T

On Wednesday 14 November 2018, the main rotor of LN-OAN struck the spire on a mast in connection with a nearby mast being dismantled and transported away. This resulted in damage to the rotor blades and subsequent emergency landing. The incident would probably have been avoided if the safety margin between the helicopter and the obstacle had been greater. The safe job analysis did not reveal that the "longline" was too short to provide the necessary safety distance.

The Accident Investigation Board Norway recommends that the Civil Aviation Authority, as head of the Aviation Safety Forum for operators of inland helicopters, ensure that the forum continues the effort to improve the operators' methods for risk assessment of operations in general, and the associated safe job analysis for each job in particular. This can increase the likelihood that all aspects of the relevant hazards are identified, including distance to obstacles, and that the outcome is effective.

Safety recommendation SL no 2019/03T

On Wednesday 14 November 2018, the main rotor of LN-OAN struck the spire on a mast in connection with a nearby mast being dismantled and transported away. This resulted in damage to the rotor blades and subsequent emergency landing. The incident would probably have been avoided if the safety margin between the helicopter and the obstacle had been greater. The safe job analysis did not reveal that the "longline" was too short to provide the necessary safety distance. In particular, it is important that the safe job analysis reflect different challenges associated with the relevant mission, and thus used as a safety net and active barrier to adverse events.

The Accident Investigation Board Norway recommends that the Civil Aviation Authority, in its supervisory work, evaluate the safe job analysis to verify that these are adequate for the relevant missions.