CHC Airbus Helicopters EC225 LN-OJF Accident (29 April 2016) Investigation Timeline

On 29 April 2016, while making a return flight to Bergen-Flesland Airport, Norway from the Statoil Gullfaks B offshore installation, CHC Helikopter Service Airbus Helicopters EC225/H225 LN-OJF broke up in flight, with wreckage falling on land and in coastal waters at Turøy, west of Bergen, Norway.  The 13 people on board died in the accident.  Witnesses captured video of the main rotor falling separate from the fuselage.

https://www.youtube.com/watch?v=G9yrX0gaVug&feature=player_detailpage

The independent Accident Investigation Board Norway (AIBN - the Statens Havarikommisjon for Transport [SHT] in Norwegian) is leading the LN-OJF accident investigation in accordance with the International Civil Aviation Organisation (ICAO) Annex 13 on air accident investigation. On the day of the accident the local aviation regulator, the Norwegian Civil Aviation Authority (the NCAA or Luftfartstilsynet) and then the UK CAA issued operational Safety Directives temporarily prohibiting the use of the type for Commercial Air Transport (CAT):

We have previously examined the EC225 Main Rotor Head and Main Gear Box Design in detail in a popular background article.

EC225 MGB Schematic (Credit: Airbus Helicopters via Step Change in Safety)

EC225 MGB Schematic (Credit: Airbus Helicopters via Step Change in Safety)

EC225 MRH and MGB (Credit: Airbus Helicopters via Aerobuzz with Aerossurance Labelling)

EC225 MRH and MGB (Credit: Airbus Helicopters via Aerobuzz with Aerossurance Labelling)

Initial Investigation Progress and Early Regulatory Action

On 1 May 2016 the AIBN issued the following press release: The Helicopter Accident: The work continues

Helicopter wreckage was retrieved from land and the sea bottom Saturday [30 April 2016] and was then transferred to Haakonsvern naval base (Bergen) by ship.

CHC H225 LN-OJF Salvage

Wreckage of EC225 LN-OJF (Credit: AIBN)

The combined Flight Data and Cockpit Voice Recorder was retrieved from the wreckage Friday night [29 April 2016].

CHC H225 LN-OJF CVFDR

The Memory Unit Retrieved from the Honeywell Cockpit Voice / Flight Data and Recorder (CVFDR) of EC225 LN-OJF (Credit: AIBN)

The unit was taken to AAIB in England where the process of downloading data has started. Today, Sunday [1 May 2016], the work continues with search for more parts of the helicopter wreckage both at sea and on land. At the same time, the main wreckage and the large components are brought to Haakonsvern (Bergen) for further investigation.

On 2 May 2016 AIBN issued an update: The Helicopter Accident: Data from the combined FDR and CVR retrieved. Data is of good quality

CHC H225 LN-OJF Wreckage Transport

Movement of Wreckage of EC225 LN-OJF (Credit: AIBN)

On 3 May 2016 the EASA, the competent authority for airworthiness across the EU and other EASA Member States, issued Emergency Airworthiness Directive (EAD) 2016-0089-E. This called for a mandatory inspection before next flight to:

Check the correct installation of the Front and Right Hand and Left Hand Rear MGB suspension bars in accordance with the instructions of Airbus Helicopters (AH) EC225 Alert Service Bulletin No.53A058.

It also calls for the precautionary examination of the MGB Magnetic Chip Detectors (MCDs), MGB oil filter and M’ARMS Health and Usage Monitoring System (HUMS) / Vibration Health Monitoring (VHM) data. This AD did result in findings.  For example Australian SDR 510023163:

During inspections IAW EASB EC225-53A058, forward suspension bar fitting was found to have bolts more than 20 per cent below the minimum torque as specified in the MMA. Check was previously carried out per AD 2006-0163 four months ago with the results satisfactory. Two similar defects reported. P/No: 332A22161321. TSN: 863 hours/915 cycles.

By 6 May 2016, wreckage had been moved from the temporary location in Bergen to the AIBN facility at Lillestrøm, just outside of Oslo: The Helicopter Accident: The search for components is resumed

Here, the AIBN will continue its efforts to sort and analyze both components and other information. The participants in the investigation are currently working from their home bases, before the team gathers in Lillestrøm early next week to continue the work together.

On 11 May 2016, twelve days after the fatal EC225 accident, the NCAA announce that NCAA and UKCAA restrictions are being extended to the AS332L2 but partially relaxed to allow SAR training.

Neither regulator mention any new information and only cite the ‘similarities’ between the helicopters.

First AIBN LN-OJF Preliminary Report (13 May 2016)

On the evening of 13 May 2016 the AIBN issued their first preliminary report.  It confirms the aircraft was cruising at 200ft when the Main Rotor head (MRH) and mast suddenly detached. They state:

The recordings on the CVFDR showed that everything appeared to be normal until a sudden catastrophic failure developed in 1-2 seconds. The CVFDR recordings ended abruptly at the same time. There are no indications that flight crew actions were a factor in the accident. The AIBN is currently focussing on the examination of the [Main Rotor Head] MRH suspension bar assembly, the main gearbox and the main rotor head. Retrieved wreckage parts and other components are stored for future examinations as required.

EC225 / H225 LN-OJF Main Rotor Head with Aft Suspension Bars (Credit: AIBN)

EC225 / H225 LN-OJF Main Rotor Head with Aft Suspension Bars (Credit: AIBN)

CHC H225 LN-OJF

Parts from EC225 LN-OJF 2nd Stage (i.e. upper) Epicyclic Stage with a Fractured Planet Gear Placed on Top of a New Gear (Credit: AIBN)

CHC H225 LN-OJF

1st (i.e. lower) Stage Epicyclic Planet Carrier of EC225 LN-OJF (Credit: AIBN)

However, several key components are still missing. A significant sea and land search is on-going in order to retrieve these components.

CHC H225 LN-OJF Debris Plot

Debris Plot for EC225 LN-OJF Note: Time on ATC Radar Plot is UTC (Credit: Norwegian mapping Authority and AIBN)

At this preliminary stage of the investigation, detailed metallurgical examinations have not been performed. The examinations so far have not shown any sign of fatigue failure.

HUMS / VHM data from the flight has been recovered.  VHM data and maintenance records were still to be examined at this stage.

Second AIBN LN-OJF Preliminary Report (27 May 2016)

On 27 May 2016 the second preliminary report was issued by AIBN.  It stated:

A spectral analysis of the CVR data has been carried out. There was no obvious indication of an abnormality before the sudden detachment of the rotor head. The Health and Usage Monitoring System (HUMS/PCMCIA) card was retrieved and has been examined by BEA. The logic of the HUMS system is that HUMS data is saved to the card after the helicopter has landed onshore. Thus, data from the accident flight was not available. However, the system also stores some Flight Data parameters that are used for Flight Data Monitoring (FDM). On 12 May, the BEA succeeded in downloading FDM data that extended approximately 13 seconds beyond the CVFDR data. A preliminary analysis was ready a week later. It provides valuable information about the sequence of events and will be analysed further. On 20 May, key pieces of wreckage were sent to selected laboratories, including Airbus Helicopters, for detailed examination. …some key components are still missing. These components are in particular the epicyclical second stage planet gear carrier and parts of the forward suspension bar.

EC225 / H225 LN-OJF MRH, MGB and Engines (Credit: AIBN)

EC225 / H225 LN-OJF MRH, MGB and Engines (Credit: AIBN)

The official investigation team led by AIB Norway (AIBN) met at Airbus Helicopters (AH) in Marignane on 24, 25 and 26 May 2016 with the additional participation, BEA France, AAIB UK, EASA, CAA UK and CHC. The main purpose of this 3 days meeting was to agree on further investigation of the parts that the AIBN had sealed and sent to Airbus Helicopters, and to discuss a list of possible scenarios that could explain the detachment of the main rotor.

CHC H225 LN-OJF

EC225 LN-OJF Epicyclic Ring Gear Viewed from the Right Hand Side (Credit: AIBN)

The investigation team has discussed a list of scenarios that Airbus Helicopter prepared based on fault tree analysis. At this stage, the AIBN can confirm that the scenarios under consideration include failure of epicyclic module, suspension bar (lift strut) attachment and MGB conical housing.

CHC H225 LN-OJF Conical Housing
Illustration of EC225 LN-OJF MGB Conical Housing Debris Viewed from the Right Hand Side. Note the Ring Gear Damage as Shown in the Photo Above (Credit: Airbus Helicopters via AIBN)

Airbus Helicopters issued a Safety Information Notice (SIN 3043-S-00) on 30 May 2016 that described 7 scenarios that had been / were under investigation:

  1. Epicyclic ring gear failure due to fatigue failure – rejected as inconsistent with evidence gathered
  2. Abnormal loads on the main rotor (e.g. due to impact with FOD, a flight control issue, blade damage etc)  - rejected as inconsistent with evidence gathered
  3. BBQ plate loss of attachment - rejected as inconsistent with evidence gathered
  4. Conical housing failure
  5. Jamming / seizing of the epicyclic module - rejected as inconsistent with evidence gathered
  6. Epicyclic ring gear failure following internal epicyclic module damage
  7. Suspension bar attachment failure.

Third AIBN LN-OJF Preliminary Report (1 June 2016)

The third AIBN preliminary report was issued on 1 June 2016. This contained an urgent safety recommendation addressed to EASA:

Detailed metallurgical examinations have been ongoing since 19 May. Several parts from the second stage epicyclic module were retrieved from the accident site. The epicyclic module planet gears are designed as a combined gear and bearing assembly.

Close Up on EC225/H225 MGB Main Module and Epicyclic Module (Credit: Airbus Helicopters via AIBN)

Close Up on EC225/H225 MGB Main Module and Epicyclic Module (Credit: Airbus Helicopters via AIBN)

Planet gears have a double function, acting as a gear on the outside while at the same time functioning as the outer race of a roller bearing on the inside. In order to improve wear resistance it has been given a hard outer surface through a carburization process. Among the recovered parts were two pieces which together form approximately half a second stage planet gear.

CHC H225 LN-OJF Gear Debris

Almost Half of One Particular 2nd Stage Planet Gear from LN-OJF was Recovered. It was in Two Pieces (Credit: QinetiQ via AIBN)

Examinations of these parts have revealed features strongly consistent with fatigue. The fatigue appears to have its origin in the outer race of the bearing (inside of the gear), propagating towards the web of the gear teeth. There is sign of spalling in front of the fracture surface. It cannot be ruled out that this signifies a possible safety issue that can affect other MGBs of the same type.

A View from Below of a 2nd Stage Epicyclic Stage.  Note the 8 Planet Gears and the Bearings within them (Credit: AAIBN)

A View from Below of a 2nd Stage Epicyclic Stage. Note the 8 Planet Gears and the Bearings within them (Credit: AAIBN)

Although preliminary, the AIBN considers these findings to be of such significance that it has decided to issue the following safety recommendation to ensure the continuing airworthiness of the Main Gear Box (MGB).

Safety Recommendation: Recent metallurgical findings have revealed features strongly consistent with fatigue in the outer race of a second stage planet gear in the epicyclic module of the MGB. It cannot be ruled out that this signifies a possible safety issue that can affect other MGBs of the same type. The nature of the catastrophic failure of the LN-OJF main rotor system indicates that the current means to detect a failure in advance are not effective. The AIBN therefore recommends that EASA take immediate action to ensure the safety of the Airbus Helicopters H225 Main Gear Box.

On the same day NCAA extend their Safety Directive to stop all EC225 and AS332L2 flights: NCAA SD 16/05616-9 An EASA EAD, EAD 2016-0103-E with wider applicability to the AS332L2, was coincidentally issued the same day.  This however was focused on findings from the earlier EAD:

The review of the data reported in accomplishing AD 2016-0089-E, revealed installation findings for the MGB upper deck fittings of the three MBG suspension bars, to include, among others, tightening torque values on the attachment bolts of the fittings being out of tolerance and some incorrect washers positioning in the fitting assemblies. Prompted by these findings, Airbus Helicopters (AH) issued EC225 ASB No. 53A059 (hereafter referred to as ‘the applicable ASB’ in this AD) to provide further inspection and replacement instructions for correct installation of the MGB suspension bars and attachment fittings.

On 2 June 2016 UKCAA also extended their Safety Directive to stop all EC225 and AS332L2 flights and EASA issued a flight prohibition EAD:

EASA say in the EAD (which does not affect State Aircraft, which remain under national legislation in EASA Member States):

The review of the data reported in accomplishing AD 2016-0089-E, revealed installation findings for the MGB upper deck fittings of the three MBG suspension bars. Prompted by these findings, EASA issued superseding AD 2016-0103-E for further inspection and replacement instructions for correct installation of the MGB suspension bars and attachment fittings.

Soon after EASA AD 2016-0103-E was issued, a second preliminary report from the investigation board indicated metallurgical findings of fatigue and surface degradation in the outer race of a second stage planet gear of the MGB epi-cyclic module. At this time, it cannot be determined if this is a contributing causal factor or subsequent failure from another initiating factor. Pending further investigation to determine the root cause(s) of the reported damage, and development of mitigating measures by Airbus Helicopters, EASA has decided, as an additional precautionary measure, to temporarily ground the fleet.

For the reason described above, this AD prohibits flight of the AS 332 L2 and EC 225 LP helicopters.

Airbus Helicopters stated on 2 June 2016 that:

In light of new findings from the AIBN’s preliminary accident investigation report, Airbus Helicopters supports EASA’s cautious approach. We continue to fully support the ‎AIBN, EASA, our customers and the ongoing investigation by providing information in full transparency, while working with the wider industry to ensure safety.

HeliOffshore issued a statement on 3 June 2016 that:

This combination of [regulated] processes with a detailed investigation being undertaken by AIBN, supported by Airbus and others, gives us the belief that the root cause will, in time, be fully understood; then and only then, can the appropriate corrective measures be put in place to ensure that the issue is resolved… Our commitment to the investigation remains absolute; our commitment to identifying and addressing the root cause remains absolute; our commitment through collaboration with all stakeholders, not least the offshore workforce, to only returning the aircraft to service when it is safe to do so remains absolute.

On 15 June 2016 Airbus Helicopters issued Emergency Alert Service Bulletins (EASBs) on the AS332L2 (EASB 05.01.07), the military AS532A2 and U2 (EASB 05.00.82), the EC225 (EASB 05A049) and military EC725 (EASB 05A045), which effectively are applicable only to aircraft unaffected by the EASA Flight Prohibition.  These require:

  • Inspection of the MGB oil filter and chip detectors after the last flight of the day
  • Cessation of flying with epicyclic modules which have been involved in an unusual event since new or Complete Overhaul and return for Complete Overhaul

Airbus Helicopters note the investigation in Norway is on-going and although no conclusions have been reached these EASBs have been introduced as a precautionary measure as:

…the MGB of the helicopter involved in the accident had been subject to a shock impact during road transport a few months previously.

On 3 June 2016 the US Federal Aviation Administration (FAA) also issued an EAD.

Fourth AIBN LN-OJF Preliminary Report (28 June 2016)

On 28 June 2016 the AIBN release a fourth preliminary report.

Two pieces of the recovered parts have been of particular interest. Together they make up approximately half of a second stage planet gear P/N 332A32.3335.07, S/N 10-1292. Examinations of these parts show that one of the fracture surfaces can be described as being close to 100% fatigue.

Crack In 2nd Stage Planetary Gear from EC225 LN-OJF (Credit: QinetiQ via AIBN)

Crack In 2nd Stage Planetary Gear from EC225 LN-OJF Viewing the End of One of the Recovered Pieces (Credit: QinetiQ via AIBN)

Growth of a fatigue crack requires repeated load cycles, for example through rotation of a gear or a main rotor start/stop cycle. The fatigue appears to have its origin in the outer race of the bearing (inside of the gear), propagating towards the web of the gear teeth.

The AIBN say there are similarities (but some differences) to the 1 April 2009 G-REDL AS332L2 accident. The fatigue origin apparently sub-surface near the bearing outer race, propagating outwards towards the teeth. A Computed Tomography (CT or CAT) scan conducted at the University of Southampton identified sub-surface cracking between patches of inner race surface spalling.

CT scan showing a subsurface crack propagating from the RH spalling to the left. The red colour is a frame-by-frame mapping performed by hand to highlight the crack. (Credit: University of Southampton via AIBN)

CT scan showing a subsurface crack propagating from the RH spalling to the left. The red colour is a frame-by-frame mapping performed by hand to highlight the crack. (Credit: University of Southampton via AIBN)

Therefore the AIBN have tentatively concluded:

At this stage of the investigation, the AIBN finds that the accident most likely was a result of a fatigue fracture in one of the eight second stage planet gears. It appears that the fracture has propagated in a manner which is unlikely to become detected by existing mandatory or supplementary systems for warning of an imminent failure. What initiated the fracture has not yet been determined. AIBN will also look into the follow-up of safety recommendations issued after the Super Puma accident in Scotland in 2009 [G-REDL].

The AIBN suggests the crack propagation was contrary to design assumptions that the compressive stress near the surface of the inner race would effect sub-surface cracks.  AIBN say no debris had been found previously and no procedural maintenance failures occurred.  The AIBN also suggest the defect may not be detectable by HUMS. The AIBN confirm the Time Since New (TSN) of the MGB was 1340 hours (260 hours since installation on LN-OJF on 15 January 2016).  The transit damage, mentioned in earlier Airbus Helicopters Emergency Alert Service Bulletins is still under investigation. AIBN updates are now predicted to be less regular. Airbus Helicopters have said:

Airbus Helicopters takes note of the AIBN’s preliminary report update and welcomes the significant progress made by the investigation. We continue to focus our efforts on providing assistance to the investigation team and the authorities as they work toward the identification of the accident root cause.  In parallel, we are putting precautionary measures in place to support our global customers and address potential initiating events.

On 29 June 2016 Airbus Helicopters issue EASBs on the AS332L2 (EASB 63.00.83), the military AS532A2 and U2 (EASB 63.00.38), the EC225 (EASB 63A030) and military EC725 (EASB 63A029).  These state:

As a precautionary measure, it was decided to maintain only one of the two types of epicyclic module second stage planet gears in service.

This is because:

  • The detailed design of [one type of] the planet gear bearing has an increased damage tolerance.
  • Modelling and calculation reveal a lower load level on the external race of the planet gear bearing.
  • In-service experience shows enhanced reliability.

The EASBs require the replacement of the other type within 15 flying hours. Airbus Helicopters (AH) also issued SIN 3053-S-00 on 29 June 2016 that described 7 scenarios that had been under investigation:

  1. Epicyclic ring gear failure due to fatigue failure – previously rejected as inconsistent with evidence gathered
  2. Abnormal loads on the main rotor – previously rejected as inconsistent with evidence gathered
  3. BBQ plate loss of attachment - previously rejected as inconsistent with evidence gathered
  4. Conical housing failure – “AH still assesses this as a consequence and not as a cause. Work is in progress to definitely close this scenario”.
  5. Jamming / seizing of the epicyclic module – “AH observes that the jamming event is contradicted by available evidences. Work is in progress to definitely close this scenario.”  The relevant evidence is believe to include evidence that the tail rotor continued to be powered via the MGB at impact.
  6. Epicyclic ring gear failure following internal epicyclic module damage – as discussed by AIBN (plus see below).
  7. Suspension bar attachment failure – still subject to further AH tests and EASBs on verifying individual installations to fully eliminate all concerns.

In relation to scenario 6 and the current AIBN focus, Airbus Helicopters say:

The cause for the initiation of the fatigue fracture remains to be determined. It may be the followings:

  1. Unusual event suffered by the MGB (for example a transport incident)
  2. FOD in the MGB
  3. Other MGB causes (including manufacturing process, metallurgical issues,…)

Some tests and calculation are being performed on the second stage planet gears.  The purpose of these tests is to reproduce the fatigue crack, determine its origin and better define its speed propagation.

Further Developments

UPDATE 20 July 2016: It is reported that the Norwegian Government has granted additional funding to the AIBN to cover the extra costs of the investigation:

According to reports in Norwegian media, the amount provided is said to be around five million Norwegian Krone.  However the AIBN would not confirm the amount provided by the government but said it was “enough” to help them carry out their work. A spokesman for the AIBN said: “The Norwegian Government provides funding as needed for investigations.  “When a major incident happens like this we will ask for more money as needed in addition to the regular budget.”

UPDATE 27 July 2016: Flight International report that during a half-year results call on 27 July 2016 Airbus Group CEO Tom Enders said:

…the company is making “good progress” with EASA towards understanding how soon the H225 and AS332 fleets might be returned to flight. “We are engaged in discussions with EASA to see when we can release the Super Puma fleet again. We want to get out of this situation as quickly as possible,” Enders says, noting that about 80% of the fleet remains grounded. Airbus Helicopters says talks with EASA are key to lifting the grounding, but declines to comment on any timeline for that to be achieved.

UPDATE 19 August 2016: Former Bristow Director Allan Blake writes for HeliHub: The distressed EC225 fleet – A review

UPDATE 31 August 2016: Airbus Helicopters braces for post-Turøy impact

UPDATE 5 September 2016: We are very sad to learn that one of the AIBN investigators, Edith Irgens, passed away last month (Norwegian language obituary).

UPDATE 20 September 2016: AW&ST publish: S-92 Usage Leaps After EC225 Grounding, Sikorsky Says

UPDATE 23 September 2016: Flight International publish: Market turmoil for offshore operators

19-seat-market-230916

The above graphic shows how reliant the industry is currently on a stretched S-92A fleet.

UPDATE 23 September 2016: Statoil issue their internal investigation into their handling of the accident and flight safety.

UPDATE 29 September 2016: Statoil release the English language version of their internal investigation.

The aim of this report is said to be to determine:

  1. How can Statoil’s helicopter safety-related work be strengthened?
  2. Was the emergency response to the Turøy accident handled in accordance with Statoil’s governing documentation?

They emphasise they did not aim to determine the cause of the LN-OJF accident as that is the role of the AIBN.

In their conclusions they say:

Helicopter safety is a complex assignment that is managed by several stakeholders and functions in Statoil, and it may be difficult to predict how individual decisions, taken in isolation, can affect overall safety. There is a need to strengthen safety by highlighting and better understanding the relationship between technical and commercial factors that, either individually or combined, can affect safety. With this as a starting point, a clearer flight safety strategy and associated plan of action must be prepared.

The organisation of helicopter safety-related work in Statoil appears to be complicated, with many participants and a varying understanding of each individual participant’s role. Although it is not apparent that this has impacted negatively upon the quality of helicopter safety-related work to date, the investigation team recommends that a review of the organisation of helicopter safety-related work in Statoil be conducted to ensure simplification and a clearer description of participants’ roles. This particularly applies to the distribution of roles between the departments for flight safety, air transport and procurement, and personnel with the role of Company Representative (CR).

They also comment:

Statoil’s strategy has been to utilise at least two different types of helicopter, primarily to ensure business continuity and robustness in the event of one type of helicopter being grounded for any reason. Following the accident on 29 April 2016, all Airbus H225 and L2 Super Puma helicopters were grounded, and as a result Statoil could only use the Sikorsky S-92 helicopter for offshore personnel transport. The investigation team is of the opinion that using just one type of helicopter may increase the operational risk related to personnel transport, but it does not increase the safety risk. Statoil has initiated a project to look into alternative helicopter transport solutions. The project will, amongst other things, propose a strategy for backup solutions for the existing Sikorsky S-92 helicopter and other alternative transport solutions. A recommended strategy for realising the proposed solutions will also be developed.

Another aspect examined was commercial rates and penalties:

During the contract period Statoil can make commercial dispositions that affect the helicopter operators’ financial position, including cancelling the contract or renegotiating the rates. A reduced need for helicopters, combined with a need to reduce costs, has led to an increase in the scope of such dispositions in recent years.

Several of the individuals that the investigation team has spoken with have questioned whether the “penalty” regime [for late or delayed flights] may negatively affect helicopter safety.

The investigation team believes that further work must now be done with this recommendation, and to see whether other systems that stimulate punctuality and regularity can be found, without the negative effects that are highlighted above. One possible system is described in the {2010 HSS-3] SINTEF study: “One suggestion is that fines are not imposed on the basis of single flights, rather that they are based upon relevant monthly statistics and current indicators”.

The investigation made eight recommendations in 4 areas.

  • Statoil’s organisation and activities related to helicopter services – recommendations 1, 2 and 5
  • Following up and learning from helicopter incidents – recommendation 3
  • New EU regulations – recommendation 4
  • Emergency response – recommendations 6, 7 and 8

In particular these are of most interest:

statoil-r1

 

statoil-r3

This is further discussed in an article by Allan Blake for HeliHub: Stretching Safety too Far – a Withering Safety Culture

UPDATE 7 October 2016: EASA issue AD 2016-0199 that responds to the AIBN recommendation, lifting the flight prohibition.  EASA say that following further investigation of:

…possible accident contributory factors and determined that the likely cause relates to the rupture of the second stage planet gear, which was found with fatigue and surface degradation. Although the root cause of this failure is still not fully understood, it involved cracking of the planet gear bearing outer race, some spalling and propagation of a crack into the rim of the gear, finally resulting in its rupture.

There are two configurations of planet gear.  Each features different bearings.

In depth review of the design and service data showed that one configuration has higher operating stress levels that result in more frequent events of spalling, associated with rolling contact fatigue, while the other exhibits better reliability behaviour. By limiting the type design to the gear configuration with lower stress levels and better reliability and specifying a reduced life limit, combined with more effective oil debris monitoring procedures and other operational controls, an acceptable level of safety can be restored.

Airbus Helicopters has issued AS332 Emergency Alert Service Bulletin (ASB) 63.00.83 and EC225 ASB 63A030 (single document at Revision 1), and AS332 Emergency ASB 05.01.07 and EC225 ASB 05A049 (single document at Revision 2).

In addition the Service Life Limit (SLL) of the remaining planet gear is reduced and replacement of parts involved in any unusual events (such as a lightning strike or ground handling/transport damage) is made mandatory.

UK CAA has issued a very brief statement that at this time their:

…existing restriction, prohibiting all commercial flying of this type by UK operators, is to remain in place.

We are united in our approach with the Norwegian Civil Aviation Authority. Both agencies now await further information from the accident investigation before considering any future action.

The Norwegian CAA has issued a statements in Norwegian and English.

HeliOffshore has issued an explanatory statement (as have Step Change in Safety).  They say:

HeliOffshore members who operate these aircraft types will review the evidence and determine, with customers, the implications of the EASA Directive for search-and-rescue and oil-and-gas operations – with safety being their primary consideration.

At each step, for every organisation involved, the safety of passengers and crew comes first.

Airbus Helicopters has commented:

We are providing assistance to our customers and working with related stakeholders in order to help them return their aircraft to service at the appropriate time. Meanwhile, we maintain our full support to the AIBN in the frame of the ongoing investigation.

Extensive liaison has been underway in the last few days and further engagement between the multiple stakeholders is expected in the coming days.

UPDATE 12 October 2016: In an interview with Flight International Airbus Helicopters CEO Guillaume Faury says:

“Some people say we have not understood [the root cause]. We know a lot. We are down to a small number of scenarios, which are very precise scenarios, for which we can put appropriate protections in place,” he says.

He is adamant that “it is not the case” that the Super Puma is no longer wanted by North Sea operators, but admits there has been “a significant loss of trust”.

“It is something we fully recognise and are fully aware of and we have to go through the steps to restore that trust. That has to be based on very robust, convincing, solid arguments.”

Faury says that it will now begin a wide-ranging engagement process with all stakeholders as it looks for a full return to service.

However, Faury acknowledges that the process cannot be rushed and that it must proceed “step by step”. It is a “process that’s going to take time”, he says, of which EASA’s move is only the start.

Meanwhile in an article for HeliHub, Allan Blake reports:

An Airbus source explained that they had conducted over 20,000 bench hours of tests to identify the cause of the accident, the results of which were passed to EASA.

Blake also quotes Aerossurance own Andy Evans, a former UK CAA / JAA Rotors and Transmission Specialist:

While clearly there will be a challenge to rebuild passenger confidence it’s vitally important for the whole industry (operators, their customers and all OEMs) that rational decisions are made with full understanding of the available information.

UPDATE 22 October 2016H175 helicopters add resilience to North Sea industry, safety chief says as NHV open new Aberdeen heliport.

UPDATE 28 October 2016: Many hurdles ahead before H225 can return to flight

UPDATE 6 December 2016: Statoil to Stop Using H225 Helicopter Variant Involved in Crash (though our continuing to use two AS332L1s for LIMSAR).

UPDATE 9 December 2016: Airbus Helicopters sued by three companies over H225 situation (two lessors and ERA).

UPDATE 15 December 2016: It is reported that the FAA approves return to service of H225 helicopter:

Via an alternative means of compliance (AMOC) notice, the FAA has adopted a number of measures contained in an emergency airworthiness directive (EAD) issued by European regulators in early October, designed to detect the warning signs of an imminent main gearbox failure.

“We will follow this in the coming months with [a new] airworthiness directive, but the AMOC provides the approval to accomplish what needs to be done,” says the FAA.

UPDATE 15 December 2016: Reversing the Trend: Offshore Safety in Norway

UPDATE 30 December 2016: This was our 11th most popular article of 2016.

UPDATE 3 January 2017: Airbus Malaysia have just completed a G check on a Southern Vietnam Helicopter (VNHS) AS332L2, suggesting that the type has, or is just about to resume service offshore in Vietnam.  Its not clear which oil company/companies are the customer.

UPDATE 10 January 2017:  Waypoint Leasing announced it is leasing one H225 helicopter to Global Helicopter Service (GHS), a German operator active in Africa, for utility and humanitarian support missions.

UPDATE 13 January 2017: The same week as widespread disruption occurred due to an Alert Service Bulletin on the S-92A after a tail rotor control failure, Flight International reports that Airbus Helicopters meets regulators to discuss H225 grounding.  The NCAA say:

…its representatives, along with those from the UK, attended a meeting in Marigane on 10 January to discuss the H225. Petter Haugen, acting director-general of the Norwegian CAA, says: “The purpose of the meeting was to exchange views regarding to the situation, and seek mutual knowledge and understanding.  It was a constructive meeting with an open dialogue. We will continue co-operation and dialogue regarding short- and long-term measures.”

The UK CAA confirmed that the H225 was on the agenda of a recent ‘routine’ meeting.  There is industry speculation that both nations are potentially in breech of European Law by persisting with airworthiness related operational directives following EASA AD 2016-0199 that are outside of their legal competence.

UPDATE 27 January 2017: In a Reuters article, Airbus Helicopters CEO Guillaume Faury is quoted as saying:

We don’t want to solve the problem and move forward…we want to grow out of this crisis much strong and much better.

Reuters say:

Faury said he expected Norway to release its final report on the Norwegian accident “in the next few months”.

He pledged to review processes to raise safety across the offshore industry… More monitoring and sensors could play a role.

UPDATE 2 February 2017: In a short update the AIBN seem to scotch any notion of an immanent final report.  they say:

The scope and complexity of the investigation means that it is not feasible to estimate a completion date for the final report. The investigation continues with the same high activity. Aviation authorities in Norway and Europe are continually updated about the investigation.

The AIBN intends to issue a new preliminary report on 29 April 2017, unless there are significant new discoveries necessitating an interim report in the meantime.

They comment:

The investigation is complex, and has a wide scope. So far, the metallurgical studies have been a major focus. These are efforts to map and understand why fatigue cracks could form and evolve. This work has not yet been completed.

At present time, the primary focus of the AIBN investigation is certification aspects of the main gearbox and the robustness of past and present design requirements. This includes the follow-up on safety recommendations issued by the AAIB in connection with the accident involving G-REDL and continuing airworthiness of the gearbox. This work requires good collaboration with the responsible entities, primarily the helicopter manufacturer and the European Aviation Safety Authority (EASA).

UPDATE 7 February 2017: The AIBN has also published their accident investigation and analysis methodology.  The process is divided into the following seven stages:

  • Stage 1: Clarifying the sequence of events and circumstances of the accident.
  • Stage 2: Identifying safety problems = ‘what went wrong’ in the sequence of events.
  • Stage 3: Barrier analysis.
  • Stage 4: Identifying safety factors.
  • Stage 5: Establishing the factors’ relevance (existence, influence and importance).
  • Stage 6: Considering systemic safety problems (safety issues) = areas for improving safety.
  • Stage 7: Assessing the need for safety recommendations.

aibn methodology

UPDATE 7 February 2017: Airbus Helicopters has issued an ASB for a one-time inspection to check for the presence of metallic particles in the oil cooler on EC225 and AS332L2 whose second-stage planet gears have accumulated over 300 hours of flight time since new.  This ASB is subject to EASA AD 2017-0042 in which EASA say:

…further testing investigation has delivered additional results as regards the close monitoring provisions. Those results require to amend the inspection regime in place with a one-time inspection of the oil cooler to acquire additional information on the condition of the MGB oil system. 

Airbus has commented that “this new inspection further enhances the protective measures currently in place and are part of the wider safety case addressing EC225/AS332L2 operations worldwide”.

UPDATE 8 March 2017: AIBN announce that divers from the Norwegian Naval Diving School have recovered the epicyclic gear 2nd stage planet gear carrier.

Second Stage Planet Carrier of LN-OJF (Credit: AIBN)

Second Stage Planet Carrier of LN-OJF (Credit: AIBN)

UPDATE 13 March 2017: The fate of the North Sea’s grounded Super Puma helicopter fleet could ultimately be decided by factors like public confidence not just safety assurances, UK union leader Jake Molloy today claimed.  This followed a meeting of the Offshore Helicopter Safety Leadership Group (OHSLG) in Aberdeen on 28 February 2017:

A spokesperson for the UK Civil Aviation Authority, said:

“The UK and Norwegian authorities have confirmed that existing restrictions, preventing commercial use of the H225LP and AS332L2 Super Puma helicopters in the two countries, remains in place.

“At a meeting in Aberdeen on February 28, workforce representatives, helicopter operators and the offshore industry were updated by Airbus Helicopters and the European Aviation Safety Agency on the progress that has been made on developing significant changes and inspections to the helicopter type that could, in the future, allow the UK and Norwegian authorities to lift restrictions.

“Significant information from the investigation of the tragic 2016 Norwegian accident is now available and we await further information. Any decision will be made only after extensive consultation, investigation and consideration.

At the meeting Airbus Helicopters provided an update on the progress made in relation to the LN-OJF investigation.

Step Change in Safety Executive Director Les Linklater…said: “All members were given a presentation by Airbus Helicopters providing an update on the progress made on the LN-OJF [Norway] investigation.  “The meeting was a transparent, informative and focused session to discuss advances being made into raising standards in flight safety”.

UPDATE 17 March 2017: EASA issue EAD 2017-0050-E:

Since EASA AD 2016-0199 was issued, further testing investigation provided additional results regarding the close monitoring provisions. Following those results, EASA issued AD 2017-0042 (later revised) to require a one-time inspection of the oil cooler and the reporting of findings to acquire more information on the condition of the MGB oil system. Additional analysis and flight testing determined the need to amend the inspections required by EASA AD 2016-0199 to improve the detection capability of MGB planet gear degradation. Consequently, AH issued AS332 Emergency ASB 05.01.07 and EC225 ASB 05A049 (single document at Revision 4) to provide the necessary instructions.

For the reasons described above, this AD retains the requirements of EASA AD 2016-0199, which is superseded, modifies the MGB oil filter inspections regime, additionally requires repetitive inspections of the MGB oil cooler and, depending on findings, accomplishment of applicable corrective action(s).

UPDATE 24 April 2017: The AIBN have announced they will hold a press conference in Lillestrøm Friday 28 April at 1300 hours.  Prior to that they will issue a preliminary report in English:

…in order to present an updated status of the investigation. The report contains mainly factual information available so far in the investigation. The report also contains some AIBN comments.

We will analyse the AIBN report on Friday.

Other Resources

See also:

ec225

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