https://tsb.gc.ca/eng/enquetes-investigations/aviation/2021/A21W0045/A21W0045.html
Air transportation safety investigation A21W0045
TSB has completed this investigation. The report was published on 7 September 2022.
https://tsb.gc.ca/eng/rapports-repor.../a21w0045.html Final Report
Yellowhead Helicopters Ltd.
Bell Textron Inc. 212 (helicopter), C-GYHQ
Evansburg, Alberta, 4 NM WNW
28 June 2021
Exerpts:
Metallurgical analysis of the 4 pins (part number 204-012-104-005) revealed that the failed pin (serial number FNFS90, bottom of Figure 7) was manufactured from 316 stainless steel, whereas the other 3 pins (serial numbers FNFS49, FNFS54, and FNFS75) were manufactured from H11 tool steel.
The TSB Rockwell hardness test of the failed pin averaged 7.6 on the C scale
The Bell engineering drawing used to manufacture the part number 204-012-104-003 pin specified a hardness of 50.0 to 53.5 on the Rockwell C scale as a critical characteristic of that pin. This characteristic is obtained through the double-tempering process on H11 tool steel.
The investigation determined that, when the occurrence pins were manufactured in the fall of 2018, FMC stored the raw material in its stores area by material diameter, not by type or composition. This meant, for example, that all rods that were 1 inch in diameter were stored together, regardless of the material they were made of (aluminum, carbon steel, stainless steel, brass, etc.). As a result, the onus was on the individual selecting the material for the job at hand to ensure that it was of the correct composition and specification.
On 02 October 2018, the stores department at FMC released the 8 rods of H11 tool steel to the production floor to begin the manufacturing process.
The investigation determined that the 8 rods of H11 tool steel would have yielded only approximately 320 pins.
From 12 to 14 November 2018, the rods of raw material, which varied in length from 132 to 156 inches, were cut up into 36-inch lengths and then further cut into 3.3-inch lengths. The resulting 343 pieces ...