The Bell 206B had been imported from the U.S. a few months earlier and the private owner had hired a professional pilot to manage the project and to ensure the highest level of safety of future flight operations. The aircraft maintenance engineer (AME) and an associate owned and managed the helicopter maintenance facility that had reviewed the maintenance history of the craft, performed the inspection and made the necessary minor repairs in order to obtain the certificate of airworthiness.
He had asked a young assistant-AME several days before to remove, clean and repaint the droop restrainers and the mast nut that held the rotor blades to the mast of the helicopter and when his associate observed that the wrong paint had been used as a primer, the assistant was asked to redo the job using epoxy paint.
The following morning the pilot arrived at the hangar around 09:30, and informed the AME that the owner wished to make a flight the next morning. He stated that he wanted to clear the few snags that remained before the end of the day and requested his assistance. There had been no Journey logbook entry made referring to the work that was being performed on the droop restrainers and on the mast nut.
There was no warning notice at the pilot station, no warning flag on the masthead, nor any other information referring to the outstanding work regarding these major parts rework. Around 15:30, the pilot and the AME moved the helicopter outside the hangar, got on board and started the engine. Following a few minutes of checks, the pilot lifted-off and began a hover. All seemed well and he landed to allow the owner to walk over to the craft and exchange a few words with the AME. Following the conversation, the helicopter took off for a performance check of the transponder.
Ten minutes into the flight, at approximately 15:40, the pilot informed the Area Control Center that he was returning to base. The controller explained that he was not receiving any code or altitude information from the helicopter transponder unit.
Shortly after the helicopter vanished from the radar screen. It crashed just a few kilometers from its home base. The two men met with a tragic fate. Each man had strayed away from common practices of checking and double-checking everything; machine, engine, logs, before setting out on the flight.
Transportation Safety Board (TSB) investigator found the first indication of a malfunction approximately 400m from the crash site as small pieces of Plexiglas from the helicopter canopy were found on the ground. A reconstruction of the accident seems to indicate that as the main rotor blade assembly departed the main rotor hub it struck the canopy and broke it. The remains of the main rotor hub and of the propeller blades were found about 150m from the crash site. Examination of the helicopter revealed that the mast nut, the droop restrainers and a few other parts were missing from the propeller hub assembly. The internal threads were intact and there was no sign of any attachment bolt failure.
A brief inquiry disclosed that the aircraft had departed with the main rotor retaining nut assembly missing from the craft. The parts were found on the engineer's worktable where they had been left for drying after being painted. Unfortunately this is not an isolated event! In one form or another, such accidents occur at regular intervals and with similar tragic consequences.
An AME is often called upon to serve as a mentor and this responsibility can never be taken lightly as there is always the risk of grave consequences as we have seen. The professional qualities and attributes that one has painstakingly acquired over the years should be passed on to junior technicians in the name of safety and fellowship.
The requirements of the regulations serve as a minimum basis to ensure the airworthiness of a flight and should be adhered to rigorously. A logbook entry of the work being carried out could have saved the day. The flagging of the controls in the cabin and of the mast of the helicopter would have drawn attention at a critical moment of preflight and would have enforced the fact that critical parts were being serviced.
One must always ensure that the requirements of the regulations as well as those of the manufacturer are followed diligently. Human factors influence our life and our behavior.
Courses on Human Factors and Human Performance in Aviation Maintenance are available in Canada through various organizations. These and other similar courses will go a long way in increasing the level of awareness of human factors that can influence our performance and our work.