Video footage from the fatal 29 April Norway helicopter disaster horrified the millions who saw it on television news.

The main rotor blades were filmed spinning slowly to earth like a sycamore seed while, unseen by the camera, the flightless body of the machine had plunged to impact on an island just offshore from Bergen.

The two-pilot crew and all 11 passengers – North Sea oil industry workers – died in the aircraft. It was operated by CHC Helikopter Services. Very quickly all the affected type – the Airbus Helicopters H225 Super Puma – in the Norwegian and British fleets were grounded.

This is a disaster not just for those who died and their relatives, but also for manufacturer Airbus Helicopters because, on 1 April 2009, a Bond Offshore Helicopters Super Puma also suffered main rotor separation offshore from Peterhead on Scotland’s east coast.

In that case the aircraft hull plunged into the sea killing all 16 people on board. There was no video of the accident, but ultimately the investigation determined it was caused by the catastrophic failure of a main gearbox component – the epicyclic reduction gear. The disaster aircraft in 2009 was an AS332L, a lighter four-bladed variant of the heavy-lift five-bladed H225, but the cause of the Norway crash – still unknown – already looks as if it may be very different from the Scottish case.

Perceptions of Super Puma safety were not helped when, in 2012, two UK sector EC225s (the earlier designation of the H225) were forced to ditch in the North Sea because of main gearbox loss of oil pressure. The ditchings were successful, and the component failure that caused the problem in both cases has since been fixed, but the events exacerbated the crisis of confidence over the Super Puma fleet, especially among the oil workers who depended on them for transport to and from the rigs.

A press conference given by the Norwegian Air Accident Investigation Branch on 3 May has now confirmed that the accident was the result of a “technical” cause, not some kind of crew error, and that the time between a fault indication and rotor detachment was less than one second. Data from the cockpit voice and flight data recorder is complete, says the investigator, but the nature of the mechanical failure is still being investigated and a further statement will be released when they have more information.

Meanwhile EASA has issued an airworthiness directive requiring H225 operators to check the correct installation of the main gearbox suspension bars, examine chip detectors and oil filters for metallic particles, and to download data from the vibration health monitoring system to check for exceedences. The agency describes the measures as “interim”, but the breadth of the instructions suggests a precise cause is not yet known. On 3 May Airbus put out a bulletin to operators telling them to check the main gearbox suspension bars.

In Norway, oil industry workers are being quoted in the press as saying they will not fly in H225s when they are cleared to fly again. This will make life difficult because the type is the main heavy-lift helicopter used for transporting industry workers’ between the shore and the rigs.

The accident is a huge story in the Norwegian media. Norway is not a populous country, and North Sea oil is an important industry there. Among the oil rig commuters, few of whom have much technical knowledge of helicopters and their operation, the issue is being talked about almost with superstition – a phenomenon that replicates the reaction of UK oil rig commuters a few years ago. For example, newspapers are quoting a fact that may not be causal in either of the main-rotor-loss accidents, and is probably just a coincidence, but they quote it none the less: in the case of the 2009 UK accident the aircraft underwent a rotor change on 1 March and the crash happened on 1 April, and in the case of the recent Norwegian accident the aircraft had a rotor change on 27 March and the crash occurred on 29 April.

An additional concern being aired by Norwegian oil rig commuters is the effect of increasing pressure on costs because of the global slump in oil prices. They express a worry that pressure from Statoil for rapid aircraft turnarounds reduces time for pilots and technicians to carry out checks, although they have no means of linking this factor to the accident.

Since the 2009 crash a great deal has been done to learn about – and rectify – the technical causes of that accident and of the 2012 ditchings. Also the UK Civil Aviation Authority has carried out a searching safety review of oil-support helicopter operations in the UK sector of the North Sea.

The Norwegians had gone through a similar soul-searching review after an accident in the late 1990s, but since then – until this disaster – they had enjoyed a long period of exemplary offshore helicopter safety while British operators struggled with a series of accidents and serious incidents, the most recent being a Super Puma fatal crash on approach to Sumburgh in August 2013. The latter, according to the final report, was the result of a crew flight monitoring problem, not a technical fault.

Now the extended safe period for Norwegian oil support operations has come to an abrupt end, and a nightmare has returned for Airbus Helicopters. Rapidly finding – and fixing – the cause for this accident is crucial to confidence in the Super Puma fleet. The H225 is still in production, as is the latest version of the AS332, new-build versions of which are now designated H215.

To put it all in proportion, the Puma series has been in production since 1968, originally designed and built by Sud Aviation. The Super Puma designation arrived in 1978, and it has been through a series of changes in manufacturer branding: Aerospatiale, Eurocopter, and now Airbus Helicopters. The series has had a long and distinguished service with the military all over the world as well as operating extensively in civil transport and utility roles. As Airbus Helicopters has pointed out to the restless Norwegian media, Super Pumas have racked up 4.3 million flight hours in the air.

But all this is cold comfort to nervous oil rig commuters while they await news of the accident cause, worried about a subsequent decision by the authorities to authorise the type’s return to service in Norway and UK.