On the 12th of August in 2015, the helicopter Bristow Helicopter Sikorsky S-76C+, manufactured by Sikorsky Aircraft Corporation, had left an oil rig and was going towards the Lagos Airport, in Nigeria. However, in the middle of the trip and at a height of 3,000 feet, the helicopter experienced sudden pitch ups (a severe form of a stall in an aircraft), yaw and rolling, which caused the uncontrollable descent of the machine until it crashed on the waters of the Oworonshoki lagoon. As a result, there were six deaths, including the two pilots, and other 6 crew members suffered bad injuries.
After the accident, the Nigerian Accident Investigation Bureau (AIB) conducted an investigation and prepared a report about the causes of the event. According to the AIB, “the separation of the Forward Servo Clevis Rod Assembly from the bearing and jam nut (Bell Crack Assembly), which is part of the Cyclic Control System responsible for stabilizing the attitude of the helicopter made the aircraft uncontrollable.”
In addition to that, the lack of a backup mechanical locking system in the rod assembly structure worsened the situation and lead to the disconnection of the rod from the bearing and jam nut. Another factor that also contributed to the accident was that the clevis rod fitting shank had some wear, allowing the jam nut to freely turn without any type of constraint.
Clearly, this accident was caused by design errors from the manufacturer. Thus, AIB gave some recommendations to them in their report, stating the following: “Sikorsky Aircraft Corporation should redesign the affected control pushrod assembly by introducing wire lock or lock pins as safety features between the jam nut and the pushrod to enhance better security and safety.”
Following that, Sikorsky Corporation implemented the suggested design practices, and the remodeled Sikorsky S-76C+ helicopters are now considered one of the safest ones in the world.