Mechanical failure, perception and confidence, and differing opinions about safety are all factors contributing to the successes and failures of rotorcraft. In this article, we will look at other models that have faced similar mechanical issues, some with distinctly different outcomes, and compare them to the current issues faced by the Eurocopter family of Super Pumas.
On November 5, 1986, a Boeing 234LR Chinook crashed near the Sumburgh Airport in Shetland Islands killing 43 passengers and 2 crew. The aircraft was grounded, and the resulting investigation by the Air Accidents Investigation Branch (AAIB) found the accident was caused by a failure of a bevel ring gear (gearbox) that allowed the two rotors to collide. Despite no prior history of mechanical accidents, clearance by the Civil Aviation Authority (CAA) and several test flights conducted by British International Helicopters, (who held a contract with Shell Oil Company at the time) the fears of the offshore workers could not be overcome. As a result, the oil industry sold off all remaining Chinooks which are now operated by Columbia Helicopters as non-passenger heavy-lift aircraft.
Another large offshore model, the Sikorsky S-92A, has also faced gearbox issues resulting in an emergency airworthiness directive that grounded all S-92As in 2009. Like the Chinook, these failures also resulted in catastrophic accidents. The fix for the S-92 gearbox caused controversy because it did not pass the 30 minute run-dry regulation required by the FAA, EASA, and Transport Canada Regulatory agencies. A provision of this regulation allows an exception for Category A transport helicopters; "The applicant must show that hazardous component effects are predicted to occur at a rate, not in excess of that defined as extremely remote". The FAA defines "extremely remote" as "Not anticipated to occur to each item during its total life, may occur a few times in the life of an entire system or fleet. Quantitative: Probability of occurrence per operational hour is less than one in ten billion flight hours." As of March 2013 the global fleet of S-92As has flown only 500,000 flight hours raising concerns about the application of this exception to this model. Despite the mechanical issues faced by the S-92 and concerns regarding the solution, the model continues to enjoy success, especially in the offshore transport market where 90% of the S-92As are being used.
Most recently, the Eurocopter Super Pumas have been plagued by gearbox issues. They also share similar safety fears from offshore workers, much like the Chinook 234LR, after two ditchings of the EC225 in the North Sea due to gear box failure. In fact, the initial grounding was not prompted by any civil aviation regulatory agency, but by the operators of the EC225. The further grounding by the UK and Norway aviation regulatory agencies resulted in Eurocopter trying to mitigate the impact to the operators by supplying them with gearboxes and other components to retrofit their (also effected) AS332 L1s and L2s to an older design, allowing this aircraft to be put back into service. On August 23, 2013, the crash of an AS332 caused offshore workers' to protest the continued use of the Super Pumas. Although no mechanical cause has been determined in the AS332 crash, it has raised serious concerns with the offshore workers. This is evidenced by the workers creation of a social media page protesting the continued use of Super Pumas.
Although an interim fix for the EC225 has been approved by civil aviation authorities of EASA, UK and Norway, operators have been slow to put the EC225 back into service. Currently the fix for the EC225 consists of two preventative measures; an ultrasonic non-destructive inspection (NDI) which must be performed every 8-10 flight hours, and the updated Health and Usage Monitoring Systems (HUMS) which now detects irregular vibrations in the gear shaft, allowing the pilot to safely land within two hours of detection.
The approval and implementation of these preventative measures has not allayed the fears of the workers. Can we look at the abandonment of the Chinook as an example of an issue Eurocopter might face with Super Pumas once the gearbox and the subsequent shaft cracking issues have been resolved? The ultimate solution to the problem is a redesign of the gear shaft which could take more than a year to complete. Will the extended final fix time cause confidence concerns resulting in reduced operations of Super Pumas as offshore transport or does the current demand for the S-92A and other large offshore helicopters imply more trust in the civil aviation authorities' judgment and forgiveness of past mechanical failure? Will Super Pumas make a successful return like the S-92A? It seems the question is still up in the air.