Brazilian authorities say a rupture in the pitch change rod assembly for a main rotor blade caused an Omni Taxi Aereo Airbus H160 to ditch in the Atlantic Ocean last month.
Two pilots and six passengers were on board the aircraft when the ditching happened, but were able to evacuate the aircraft safely, and were uninjured in the incident. It took place Jan. 2 — just over seven months after the aircraft joined the operator’s fleet.
The news, detailed in a preliminary report from Brazilian agency CENIPA — the Aviation Accident Investigation and Prevention Center — follows the release of an Emergency Alert Service Bulletin (EASB) from manufacturer Airbus Helicopters, and an Emergency Airworthiness Directive from the European Union Aviation Safety Agency, which mandated the replacement of main rotor pitch rod ends after 165 hours in all H160s.
The aircraft had taken off from Cabo Frio Airport, Rio de Janeiro, headed for the Deep Blue ultra deepwater pipelay and construction vessel, and the report states that the takeoff, climb and initial minutes of cruise flight were completed without incident.
With the aircraft cruising at 130 knots indicated airspeed at 4,500 feet over the sea, a rupture occurred at the upper rod end of the white blade’s pitch change rod assembly.
“From that moment on, the aircraft exhibited high-amplitude vibrations, along with variations in attitude and speed,” the report states.
About 90 seconds after the rupture, the pilots landed the aircraft in the ocean — roughly 60 miles (100 kilometers) off the coast of Rio de Janeiro.
The report notes that the aircraft’s floats inflated automatically and the passengers and crew were able to exit the aircraft and wait for rescue in inflatable life rafts.
Brazilian authorities chose to tow the aircraft to shore, rather than hoist it onto a ship, due to the risk of potential hoist failure and further damage to the H160. The towing operation lasted nine hours.
Investigators said they were able to gain flight data from the aircraft’s cockpit voice and data recorder, which provided video from the cockpit cameras and tail boom cameras, in addition to voice recordings and flight parameters.
The aircraft’s white blade had “substantial structural damage,” the report notes, including macroscopic cracks in the root where it was connected to the main rotor head.
The upper and lower rod end bearings of the white blade pitch change rod were found broken, and video from the tail boom camera showed that the rupture happened in flight.
“For the next few seconds, the white blade pitch change rod, still connected to the swashplate by the lower rod end bearing, struck the main gearbox cowling several times,” the report states. “These impacts continued until the lower bearing also broke.
“Later, the lower rod end bearing failed, the rod completely detached and remained inside the main gearbox cowling of the airframe.”
Using a scanning electron microscope, investigators found the upper rod end bearing showed characteristics consistent with fatigue. CT scans showed a permanent plastic deformation of about 2.5 degrees in banding, with the failure starting in the compressed side of the deformation.
Investigators are performing additional tests to understand how the deformation happened.
The CT scans also showed a second crack in the upper rod end bearing, just below the primary fracture that caused the rupture, along with four “microscopic cracks” at the root thread level.
The report notes that “no hypothesis has been ruled out” in the investigation, and that additional examinations and analyses are still being conducted “on all areas of interest.”
