Super Puma
In 1974 Aerospatiale in France launched a programme to develop a new medium size helicopter based on the company’s earlier AS330 Puma. Testing began and on September 13, 1978 the first prototype flew. The testing showed that the new helicopter surpassed its predecessor in every way, and in 1981 the first civilian example was delivered to an expectant customer.
Over the years, the manufacture of this type of helicopter has been carried out by three different companies due to various company mergers. Aerospatiale developed and manufactured the helicopter between 1980 and 1991, and then continued production under the name of Eurocopter, with Airbus following on from 2014. The Super Puma has also been produced in a number of more specialised variants, but the basic version is intended for transport, that itself being very flexible and appreciated precisely for its ability to be adapted to different tasks.
A more focused military version was also brought out, called the AS532 Cougar, although several military users procured the basic version in order to meet their requirements for a flexible transport helicopter. Among the variants adapted to specific tasks are those for SAR – Search and Rescue and ASW – Anti Submarine Warfare.
Apart from chasing submarines, the ASW version can even be equipped to attack surface vessels, using a powerful radar, in which case it can be equipped with two of the well-known French Exocet anti-ship missiles.
The Super Puma has also served as a transport for official dignitaries, and has for years been used by the Brazilian presidency in the form of two of the Brazilian Air Force Super Pumas for carrying the President. They have now been replaced by newer aircraft.
Across the North Sea
A niche in which the Super Puma has become well known is the transportation to and from oil platforms in the North Sea and other areas in the world. Two of the major operators are the Bristow and CHC helicopter companies. The Super Puma has several special features enabling it to manage breakdowns over the sea, and the weather in the North Sea is extremely treacherous. So even though several accidents had taken place, in most cases the passengers and crew had survived thanks to special emergency equipment, additional flying capability and more.
A Super Puma, or EC225 as it is called by Eurocopter in the Bristow company livery in 2005. Picture: Airliners.net
However the most important factor ensuring that a helicopter that for instance suffers an engine failure in flight comes down in reasonable safety, even if it perhaps gets very wet in the case of landing in the sea, is that the helicopter’s main rotor also acts as a kind of parachute.
In the case of an engine failure, the pilot can quickly release the drive to the main rotor. In modern helicopters this takes place automatically to prevent the rotor from being broken apart by its torque. When the main rotor has been disconnected from its engine’s drive shaft, only the airflow keeps it rotating. As the helicopter then begins to descend, the air flow keeps the rotor turning, thus braking the fall and allowing the pilot to make a controlled descent and landing. This is called auto-rotation. It is therefore not completely wrong to say that every helicopter has a built-in parachute. This means that an engine failure, which for a fixed wing aircraft would create a major problem and in some cases force the pilot to abandon the aircraft in the air can instead for a helicopter be resolved without a great deal of drama.
Nevertheless, this type of helicopter has over the years suffered a number of accidents associated with oil platforms, that have ended in total catastrophe and which to start with were not entirely explicable. These accidents led to the type initially gaining a bad reputation although the advantage of using a helicopter was paramount.
The first North Sea incident occurred on March 14, 1992 when a Super Puma went out of control and crashed, with 11 out of the 17 on board being fatally injured. The next serious accident took place when a helicopter with 12 on board crashed on the way to the Norwegian Norne oil field. It turned out that there had been a catastrophic fault in the main gearbox. The fault was of such a nature that the main rotor had not disconnected and auto-rotation was not possible. The crash was investigated by, among others, the AAIB, the British Air Accident Investigation Branch, the report from which concluded with a number of recommendations and changes. The manufacturer at the time, Eurocopter, only partially accepted these.
Sheer bad luck?
On April 1, 2009 there was a catastrophic accident to a Super Puma over the North Sea off Scotland in which all 16 on board perished. The AAIB also investigated this accident and it was demonstrated that the fault was once again related to the main gearbox, specifically the planet gears, which suffered a catastrophic failure. This however did not lead to further action, partly because not all the wreckage was recovered so that there was some uncertainty about the cause, so this type of helicopter continued in use to the same extent as before.
Illustrations showing the construction of planet gears. Picture: Wikimedia commons
However on April 29, 2016 an accident took place that would have repercussions all over the world. CHC’s Service flight 241 consisted of a Super Puma that was to transport a group of oil workers to an oil platform. But the flight ended near to Turoy outside Bergen, and all 13 on board were killed. This time there were eyewitnesses close by, and the crash was filmed. One of the films showed the complete main rotor sailing down in lonely majesty. It had completely detached. The Norwegian Accident Board received assistance from Great Britain and France, and the investigation showed that once again it was the main rotor gearbox that had detached after suffering a fatigue fracture. This accident was a clear reminder of the earlier catastrophic crashes that were related to the same planet gears.
Grounded
The investigators drew clear parallels, above all to the accident in 2009 when again the main rotor had obviously detached completely and the damage was similar. The Norwegian investigation pointed out that the investigation into the 2009 crash was unable to come to all the necessary conclusions to prevent yet another main rotor loss, because vital parts of the wreckage could not be found. The investigators stated that the fault had occurred much earlier than what the manufacturer had determined would be the maximum number of flying hours, in this case stated to be 4,400 in all. In addition it turned out that they could not find a single example of a planet gear of this particular type that had not been changed before that limit, due to inspections discovering that they were defective.
Airbus was the new manufacturer, and they claimed that they had not seen any reason to suspect this type of problem to have caused the crash in 2016 already after that in 2009. However by 2016 several operators and even authorities had decided to apply temporary grounding to these helicopters while detailed investigations were being carried out. When the final Norwegian report was released in 2018 the authors encouraged the European flight safety authority, EASA, to introduce new requirements for the certification of heavy helicopters and to implement examination for cracks in various vehicle bearings, also for manufacturers themselves to perform such checks. The investigation found that the pilots in the 2016 accident were given no warning at all that anything was wrong prior to the main rotor detaching.
Finally, the Norwegian report recommended that EASA should demand that helicopter gearboxes must be fail-safe and that no internal fault in the main gearbox should lead to the main rotor coming off.
Airbus continues
Airbus deeply regretted what had happened and officially announced that the work done after the accident had resulted in the helicopter now meeting the strictest safety standards set by authorities the world over. The company also assured that it continuously made every effort to follow up and develop its work on safety. It maintained in 2018 that no manufacturer or safety-responsible authority anywhere in the world had ever seen a similar fault, and claimed that deficient maintenance was a contributory factor to the fault. On the other hand the companies flying this type of helicopter and the trade unions claimed that the entire responsibility fell upon Airbus. Airbus in the end did redesign certain construction details and reduced the time between changing the planet gears. Time will tell if this will be enough to restore confidence.
At the same time one must remember that this type of helicopter has seen service in many locations, among others by various Defence forces, without having been afflicted by similar disasters, at least not to any greater extent than could be expected. Taking into account the difficult environment and the tough financial conditions suffered by aviation operating in oil fields, it is perhaps more understandable that this type has been affected so much by accidents.
