Litany of mistakes led to 16 helicopter deaths

The helicopter plunged from the sky, killing everyone on board, seconds after one of the pilots had sent a routine radio message stating that the helicopter was “serviceable”.

The chopper disintegrated as it plummeted from 2,000ft into the North Sea at 170 knots, when its main rotor gearbox failed, its massive rotor blades ripping from the body of the aircraft and severing the tail from the fuselage.

A detailed report, published today by the government’s Air Accident Investigation Branch (AAIB), has pinpointed a series of misunderstandings, mistakes and failures in communication that led to the root cause of the mechanical failure in the gearbox going undetected.

The AAIB’s 209-page report by Keith Conradi, the Chief Inspector of Air Accidents, reveals that evidence of potential problems in the gearbox had gone undetected during a maintenance inspection on 25 March, 2009 – exactly a week before the disaster.

That failure followed an exchange of e-mails and tele-phone conversations between the manufacturer, Eurocopter, and the helicopter operator, Bond.

A small magnetic particle found on a chip detector on the aircraft had been “misidentified” as a tiny fragment of silver or cadmium scale instead of nickel or carbon steel, effectively ruling out the need to carry out additional inspection procedures.

Bond had originally initiated a plan to remove the gearbox and replace it with a unit from another helicopter. But the plan was abandoned.

The AS332L2 Super Puma, with two pilots and 14 oil- workers on board, had been on a routine flight to Aberdeen heliport from the Miller platform when it crashed, 11 miles north-east of Peterhead. The main rotor gearbox suffered a catastrophic failure – caused by an undetected fatigue crack – 50 minutes into the flight while the Super Puma was cruising at 2000ft.

The investigation by the AAIB focused on the main rotor gearbox (MGB) and its maintenance records.

According to the report, a single metallic particle had been found on one of the two magnetic chip detectors fitted to the main rotor gearbox during a maintenance inspection on 25 March, 31 flying hours before the disaster.

The report states: “As a result of the discovery of the magnetic particle, the operator had initiated a plan to remove the MGB and replace it with a unit from another helicopter undergoing heavy maintenance.”

But the gearbox was never replaced. The report reveals that because engineers had also observed an “abnormal vibration trend” in a readout for one of the gears, they had decided to contact Eurocopter’s specialists for advice by telephone as they thought they were dealing with a complex main rotor gearbox problem.

“All the subsequent communication between the operator and manufacturer took place using a combination of telephone conversations and e-mail exchanges,” the report states. “The use of verbal and e-mail communication between the operator and manufacturer on 25 March led to a misunderstanding or miscommunication of the issue.”

An engineer had removed the particle and mounted it on a debris slide. Engineers later examined the particle and came to the conclusion that it was piece of scale and either silver or cadmium plating. In accordance with the maintenance task card, the particle was deemed “unimportant” and did not require the gearbox to be removed from service or to be put on “close” monitoring.

“The gearbox was declared serviceable by the operator and its planned replacement cancelled,” the report reveals.

The AAIB states: “Had the particle been identified as nickel or carbon steel, then the helicopter should have been put into close monitoring. However, as the particle was misidentified as silver or cadmium, the maintenance task card indicated that the operator did not need to carry out any additional inspection requirements.

“Although no direct discussion with the manufacturer’s mechanical specialists took place, the operator’s engineers nevertheless believed that the manufacturer was aware that a particle had been found on the epicyclic chip detector. They therefore assumed that the e-mail provided by the manufacturer giving a series of ‘recommended’ maintenance actions provided all the actions needed to determine if the main rotor gearbox should remain in service.”

The report lists a total of 17 recommendations for safety-related improvements, most of which were contained in previous interim reports.

Jim Ferguson, the leading Scottish-based aviation writer, said: “The report suggests that there were missed opportunities but, with the benefit of hindsight, these were perhaps excusable.”

Robert Paterson, Oil & Gas UK’s health and safety director, said: “While the AAIB report confirms that neither the actions of the crew nor the weather were factors in the accident and that the helicopter maintenance regime satisfactorily complied with existing regulations, it does make 17 recommendations.

“A number of these were highlighted in the AAIB’s interim reports and have already been addressed and applied by the helicopter operators in the two years since the accident.

“The new recommendations focus on additional monitoring of technical components and the Helicopter Safety Steering Group will conduct its own detailed review of these recommendations and will focus on monitoring their implementation.”

Bill Munro, managing director of Bond Offshore Helicopters, said: “The report contains no recommendations for action by Bond.

“Following earlier interim recommendations by the AAIB, the manufacturer’s procedures have been strengthened and Bond, along with others in the industry, implemented those changes immediately.”

A spokesman for Eurocopter said: “Eurocopter has proactively initiated the implementation of a number of these modifications before the safety recommendations were issued.”

He added: “Eurocopter remains committed to working closely with the regulatory authorities, investigators and its operators to prevent the risk of accidents.”

In June 2009 three of Scotland’s leading legal firms united to form a joint advisory group to represent a number of the families bereaved in the disaster. Earlier this year, in a separate action, the partners of the two pilots who were killed in the tragedy raised a multi-million-pound legal action against Bond Offshore Helicopters in the Court of Session.

Lisa Gregory, a partner with Balfour & Manson who is the spokeswoman for the main families legal group, said last night: “The families of those lost in the disaster have endured a lengthy wait for information about the causes of the accident, which is indicative of the extensive investigations carried out by the AAIB. The report makes a number of recommendations. It is vital that these recommendations are implemented immediately in order to restore confidence in aviation in the North Sea and beyond.

“We will all take time now to consider the report and the AAIB’s findings while we wait to hear from the Scottish ministers, Crown Office and Grampian Police if there is to be a public inquiry, a fatal accident inquiry or any criminal proceedings.”