> People at large simply cannot be bothered to care about anything, including torque specs for freakin' AIRLINERSIt may have not been operator error with the torque wrench. Maybe the torque wrench itself was miscalibrated. Maybe the bolt had a flaw in the metal. It seems too early to make conclusions.
An example of flawed bolts on aircraft in an excerpt from https://www.sciencedirect.com/science/article/pii/S136970210...:
A bolt from an aircraft flap control unit fractured in the threaded region of the shank near the shoulder with the head upon installation after a major service. A metallurgical investigation was carried out to identify the cause of failure. The bolt was manufactured from cadmium-plated, high-strength steel. Material checks carried out on the bolt showed that it conformed to the required specification and was found to have an approximate ultimate tensile strength of 1380 MPa.
The fracture surface of the failed bolt was examined using SEM to identify the mode of fracture and determine if pre-existing defects were present that could account for the unexpected failure. The fracture surface exhibited two distinct modes of failure. [...]
The embrittlement in this case was attributed to the cadmium plating, which is applied to the bolts to provide corrosion protection to the steel. Hydrogen is evolved during the plating process, which becomes absorbed by the steel. The cadmium plating acts as a barrier to hydrogen diffusion at ambient temperature so that the hydrogen becomes ‘trapped’ in the steel. In high strength steels (>1100 MPa) this leads to embrittlement. To overcome this problem, high strength steel fasteners, which have been cadmium-plated, are baked at 175–205°C for 24 hours to allow hydrogen to diffuse through the cadmium. In this case, failure of the bolts was caused by insufficient baking after plating, which gave rise to hydrogen embrittlement.