CHC Helikopter Service Flight 241

CHC Helikopter Service Flight 241

A Eurocopter EC225LP Super Puma, similar to the one that crashed
Accident
Date	29 April 2016 (2016-04-29)
Summary	Investigation results pending, rotor failure reported
Site	Skitholmen, Øygarden, Hordaland, Norway 60°27′8″N 4°55′49″E
Aircraft type	Eurocopter EC225LP Super Puma
Operator	CHC Helikopter Service
Registration	LN-OJF
Flight origin	Flesland Airport, Bergen, Norway
Stopover	Gullfaks B platform, North Sea
Destination	Flesland Airport, Bergen, Norway
Passengers	11
Crew	2
Fatalities	13 (all)

On 29 April 2016, a CHC Helikopter Service Eurocopter EC225 Super Puma helicopter, carrying oil workers from the Gullfaks B platform in the North Sea, crashed near Turøy, a Norwegian coastal island 36 kilometres (22 mi) from the city of Bergen. Several witnesses reported initially seeing nothing untoward with the helicopter flying steadily, before the sound suddenly changed and it started to sway. A moment later its main rotor assembly detached from the aircraft and the fuselage plummeted to the ground and exploded into flames.

All thirteen crew and passengers died in the crash.

Aircraft

The accident aircraft was an EC225LP Super Puma helicopter, manufactured by Eurocopter (now named Airbus Helicopters), registration LN-OJF.

Background

At 10:05 local time (UTC+2), HKS241 took off from Bergen's Flesland Airport, five minutes behind schedule. It arrived at the Gullfaks B platform on time and departed at 11:16, carrying two pilots and eleven passengers, employees and subcontractors of Norwegian oil company Statoil. It was scheduled to land back at Flesland Airport at 12:08.

Crash

At 11:53, as the helicopter approached Sotra off the coast of Bergen, several witnesses observed the flight, stating that nothing was out of the ordinary until the sound suddenly changed and the helicopter started to sway. Moments later the main rotor assembly of the helicopter detached, causing a sudden drop in speed and altitude, as confirmed by flight telemetry. With all control lost, it crashed on the islet of Skitholmen between the islands of Turøy and Toftøy at 11:54:35 local time and exploded on impact. Most of the wreckage then slid off the islet into the sea. A video recording of the detached main rotors spinning to earth was made shortly afterwards. The rotor came to rest several hundred metres away on the island of Toftøy. According to flight tracking data, the time between the detachment of the rotor and the crash itself was only eleven seconds, with the helicopter diving 640 metres (2,100 ft) in that time.

Response

At 11:55, local police received reports of a helicopter crash. Six minutes later, at 12:01, this was relayed to the national rescue service. Rescue workers, police and fire fighters arrived at the scene at 12:20, and the wreckage was located partially submerged soon after. At 13:15, authorities confirmed that the wreckage had been found, and that they did not expect to find survivors.

Norwegian Prime Minister Erna Solberg described the crash as "horrible". King Harald V and Queen Sonja cancelled a visit to Sweden that was to have marked King Carl XVI Gustaf's 70th birthday.

Groundings

Shortly after the accident oil companies and helicopter operators voluntarily grounded similar helicopters until further notice, except for aircraft being used for search and rescue purposes. This was later followed by a grounding by the Civil Aviation Authority of Norway, specified to public transport flights and commercial air transport operations with EC225LP helicopters. Later that day the British Civil Aviation Authority issued a Safety Directive which grounded all EC225LP helicopters on the United Kingdom Civil Aircraft Register, or flying in United Kingdom airspace, except for aircraft being used for search and rescue purposes. On 30 April, Airbus Helicopters issued a Safety Information Notice expressing their support of the decision to put all commercial passenger flights with Super Puma helicopters of model EC225LP "on hold". Other versions of the Super Puma were not included in this decision.

On 1 May Airbus Helicopters stated in a press release that "Considering the additional information gathered during the last 48 hours, Airbus Helicopters’ decision, at this stage, is to not suspend flights of any nature for the EC225LP". They did not specify the nature of the additional information leading to this decision.

On 11 May the Norwegian Civil Aviation Authority and the UK Civil Aviation Authority jointly agreed to extend the grounding, now also including Super Puma helicopters of model AS332L2. The decision was based on similarities between the two helicopter models.

On 2 June the Norwegian Civil Aviation Authority and the UK Civil Aviation Authority extended the grounding of EC225LP and AS332L2 helicopters, now also including search and rescue flights. The updated directives were results of a recommendation in the preliminary report published by the AIBN on 1 June. Later that day the European Aviation Safety Agency decided to prohibit all flights with EC225LP and AS332L2 helicopters in Europe. On 3 June the US Federal Aviation Administration (FAA) issued a directive prohibiting flights with EC225LP and AS332L2 helicopters.

The similar military Eurocopter AS532 Cougar and Eurocopter EC725 of Germany and Brazil were grounded around 7 June in response to the accident, and the South Korean Surion was grounded in July 2016. By July 2016, 80% of the world fleet was on ground. The French military continued to operate its fleet.

Crew and passengers

On its final flight the aircraft was carrying eleven passengers and two pilots. Authorities confirmed that eleven of the people on board were Norwegian, with one British passenger and one Italian crew member. The eleven passengers were employees of six different companies: Halliburton (four employees); Aker Solutions (three); and one employee each of Statoil, Schlumberger, Welltec and no. On 2 May the names of all the crash victims were released.

Investigation

The Norwegian Accident Investigation Board (AIBN) is responsible for investigating aviation accidents in Norway. The British Air Accidents Investigation Branch (AAIB) and French Bureau d'Enquêtes et d'Analyses pour la Sécurité de l'Aviation Civile (BEA) each dispatched a team of investigators to Norway to assist the AIBN in its investigation. Representatives from Airbus Helicopters and engine manufacturer Turbomeca were part of the BEA team. The European Aviation Safety Agency (EASA) also participated in the investigation.

The aircraft's combined cockpit voice recorder (CVR) and flight data recorder (FDR) was sent to the AAIB in the United Kingdom for data retrieval. Data were successfully downloaded on 1 May and sent back to the AIBN which confirmed that the received data were of good quality and useful for further investigation.

On 1 May, the BBC reported that the helicopter had been forced to land on 26 April, over fears of a technical problem after a cockpit warning light had illuminated a few minutes into a flight.

In a press conference on 3 May, the AIBN stated that the initial investigation and analysis of data from the combined FDR and CVR convinced them that pilot error could be ruled out and that there were no indications of any malfunction until one second before the end of the recording, which they assumed was the moment when the rotor detached. An AIBN spokesman said the accident was down to a technical fault and "not an accident caused by human error". Later that day Airbus Helicopters updated their press release bulletin with a request for verification of the correct installation of all main gearbox suspension bar attachments for the EC225LP. They also stated that "similar measures will be published shortly for the EC725AP in a specific ASB" (Alert Service Bulletin).

On 13 May the AIBN released a preliminary investigation report containing a brief update on the progress and findings two weeks into the investigation. The report did not contain any conclusions or recommendations.

On 27 May the AIBN released an update to the preliminary investigation report where they confirmed that scenarios under consideration included failure of epicyclic module, suspension bar (lift strut) attachment and MGB (gearbox) conical housing. On the same day Airbus Helicopters updated their press release bulletin and stated that in their opinion only failure of the attachment of a suspension bar could be assessed as probable based on the information available by that date, an opinion also stated by Airbus during a safety meeting on 20 May.

On 1 June the AIBN released an update to the preliminary investigation report including an urgent safety recommendation to the European Aviation Safety Agency. The recommendation was based on metallurgical examinations where signs of fatigue in parts of the second stage planet gear were found.

The gearbox had suffered "unkind treatment" (road accident) during transport in Australia, and was repaired before being mounted in LN-OJF. On 15 June, Airbus requested operators to check for metal residue in oil and to report unusual gearbox events.

On 28 June the AIBN released a new preliminary report where they stated that the most likely cause to the accident was a fatigue fracture in one of the second stage planet gears. They had not yet determined what initiated the fracture. AIBN draws similarity to the 2009 Bond Helicopters Eurocopter AS332 crash, also caused by a gearbox fracture. Whereas particles had been detected in the Scottish gearbox's oil prior to the crash, no such indication was present for the Norwegian gearbox.

See also

• 2009 Bond Helicopters Eurocopter AS332 crash
• Helikopter Service Flight 451

External links

• Main AIBN page for the accident
• Helikopterstyrten i Hordaland - detailed information about the accident (in Norwegian)
• Investigation timeline
• EC225/H225 Main Rotor Head and Main Gear Box Design