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Wrong type of steel used in failed part led to fatal Evansburg helicopter crash: TSB

A Bell model 212 like the ones that crashed near Evansburg, Alta. on June 28, 2021. Transportation Safety Board of Canada (TSB)

A helicopter crashed while fighting a wildfire about an hour west of Edmonton because a part that held the rotors onto the aircraft failed, the Transportation Safety Board of Canada (TSB) revealed in its final report on Wednesday.

The crash happened at around 6 p.m. on June 28, 2021, when the Yellowhead Helicopters Bell Textron 212 helicopter was helping fight a forest fire near Evansburg.

The helicopter was approaching a makeshift landing area to pick up a group of firefighters when the TSB said one of the main rotor blades separated from the rotor head assembly.

The second rotor blade and rotor head assembly then broke free and the helicopter crashed. The pilot, who was the only person on board, died and a post-impact fire destroyed the chopper.

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The crash happened in a remote area of muskeg west of Highway 22 and north of Highway 16, where a wildfire was burning.

Map showing the location of the staging area and Evansburg wildfire helicopter crash site, with inset photos of the 2 main rotor blades (Blade A and Blade B). Google Earth with TSB annotations

The TSB’s investigation found one of the main rotor hub strap retaining pins — a critical part for flight safety — was made from a type of steel that was weaker than the steel required by design.

As a result, the pin failed mid-flight and the rotor blade was sent flying.

The rotor hub straps and pins had just been replaced the week before during scheduled maintenance and had only accrued about 21 hours of flight time when they failed.

An excerpt from the TSB report reads:

“The investigation determined that the pin was manufactured from 316 stainless steel instead of tempered H11 tool steel as designed. Because 316 stainless steel has approximately ⅓ the tensile strength of H11 tool steel, the pin was unable to withstand the forces applied to it during normal operations. As a result, the pin failed in a shear mode approximately 21.4 hours of time in service after being installed in the rotor head assembly.”

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The sheared-off pin that failed on the Yellowhead Helicopters Bell Textron 212 helicopter that crashed near Evansburg, Alta. on June 28, 2021. Transportation Safety Board of Canada (TSB)

Fore Machine Company in Texas manufactured the pins for Bell Textron, and the TSB said for undetermined reasons, the quality control systems in place did not identify the non-conforming main rotor hub strap retaining pins; thus, they were not removed from the supply chain.

The TSB found at the time the pins were being manufactured, the company stored the raw materials by diameter or profile — not by material composition.

It was up to individual workers to ensure that the correct materials — carbon steel, aluminum, titanium, 316 stainless steel, H11 tool steel etc. — were being selected.

“If the segregation and storage of material do not include processes to ensure that the correct material for a job is selected, there is a risk that incorrect material will be selected.”

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The TSB also found only some of the raw materials’ metallurgical properties were tested before the pins were made.

“If aerospace product manufacturers do not test sufficient samples of all raw material lots used to manufacture flight safety critical aircraft parts, there is a risk that non-conforming material will be inadvertently introduced into the manufacturing process,” the TSB report said.

The investigation found the pins made from the wrong type of steel were basically identical to the correct ones, so aircraft maintenance technicians would have had no reason to believe they were faulty.

Although the defective strap pins were only reported on Bell 212 helicopters, the pins could be installed on Bell 204B, 205A-1 and 205B helicopters as well.

A few weeks after the crash, Bell issued four alert service bulletins to make sure any other inadequate pins were to be replaced with ones that conformed to aviation standards.

That same day, Transport Canada grounded all four types of Bell helicopters, issuing an emergency airworthiness directive mandating all be inspected and faulty pins replaced.

The U.S. Federal Aviation Administration and the European Aviation Safety Administration did same thing that week.

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As that time, Transport Canada said there were 133 Canadian-registered Bell 212 helicopters; in addition, there were 49 Canadian-registered Bell 205A1 and B and 18 Canadian-registered Bell 204B helicopters that may have been affected.

Fore Machine Company ceased operations and closed in November 2021.

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