Mx Process ID’d as Possible Issue in H160 Ditching

While flying six passengers from Cabo Frio Airport (SBCB) to the Deep Blue Maritime Unit off the coast of Rio de Janeiro on January 2, the two pilots of an Omni Helicopters International Airbus H160 “suddenly felt high-amplitude vibrations,” according to Brazil’s Cenipa accident investigation and prevention bureau. “The crew made an emergency landing at sea.”

The H160’s float system was successfully deployed, and the passengers and crew climbed into life rafts and were soon rescued by navy personnel, with no injuries reported.

According to the Cenipa preliminary report, the H160 had been flying at 4,500 feet and 130 kias when “a rupture occurred at the upper rod end of the white blade’s pitch change rod. [The five rotor blades are color-coded for maintenance purposes.] From that moment on, the aircraft exhibited high-amplitude vibrations, along with variations in attitude and speed.” The H160 touched down on the water 90 seconds later. After the incident, the H160 was carefully towed over nine hours to the port of Pavuna, where it was lifted by a crane and then moved into a hangar.

Significant amounts of information were available from undamaged recording devices that included an aircraft management computer, airborne communication server, remote media device, dynamic monitoring acquisition unit, cockpit voice and data recorder (CVDR), cockpit camera, and tail boom camera. Representatives from France’s BEA investigation agency, Airbus Helicopters, Safran Helicopter Engines, and EASA were onsite to assist with the investigation.

During the assessment of damage to the helicopter, the white blade’s root was found to be cracked near where it connects to the main rotor head. The blade’s lead-lag damper was deformed due to overextension. The blade’s pitch change rod upper and lower rod end bearings were both broken, and the CVDR data showed that the rupture occurred during flight. Helpful to investigators was the imagery from the tail boom camera, which captured the moment that the rod end broke. The rupture started at the rod end bearing, but for a few seconds, the pitch change rod remained attached and hit the main gearbox cowling. Then the lower rod end bearing broke, and the pitch change rod failed and detached completely, according to the report.

While investigators found that the fracture surfaces on the failed upper rod end bearing showed characteristics of fatigue, the report noted, “There was no indication of evident crack initiator (such as pitting corrosion or signs of impact damage) at the initiation area.” The lower rod end bearing showed “signs consistent with overload failure.”

Early in the investigation, Airbus published a safety information notice and an emergency alert service bulletin for all H160-B models requiring immediate replacement of main rotor pitch rod ends. The bulletin was referenced in a January 8 EASA emergency airworthiness directive requiring mandatory replacement of certain upper and lower pitch rod end bearings every 165 flight hours. A subsequent Airbus emergency alert service bulletin to inspect for permanent plastic deformation of main rotor pitch rod ends was also made mandatory by another EASA AD.

In an update to the preliminary report, however, Cenipa added new information that points to possible maintenance involvement in the rod end failure. Security camera recordings in the Omni maintenance hangar captured work done on December 24, including a swashplate functional test.

During this test, the main gearbox (MGB) fixed cowling is supposed to be removed and the pitch change rods isolated and immobilized. According to the Cenipa report, “Images from the cameras showed that during maintenance services, the RH [right-hand] MGB fixed cowling was installed on the aircraft, and that the pitch change rods were neither secured nor immobilized while the main rotor blades were turning.

“Images from the cameras also showed that during maintenance services, one of the pitch change rod assemblies became stuck on the RH MGB fixed cowling while the main rotor blades were being turned clockwise.

“The stuck pitch change rod disrupted the main rotor blades’ rotation. The technician performing the maintenance services attempted to continue turning the main rotor for approximately 6 (six) additional seconds, until the rotor became unable to turn due to interference between the stuck pitch change rod and the RH MGB fixed cowling.

“The technician tried to release the stuck pitch change rod from the left side without success, then walked down the LH platform and climbed to the opposite side by the maintenance steps (no RH platform was installed). After climbing on the opposite side, the technician tried to release the stuck pitch change rod several times without success. Finally, the technician rotated the main rotor blades counterclockwise, and the stuck pitch change rod was released.”

The Cenipa report was careful to point out that investigators couldn’t determine from the video if the stuck pitch change rod was the white blade’s rod. “It is not possible to conclude whether the stick observed in the video recording contributed to the permanent plastic deformation observed at the white blade upper rod end bearing.”

The investigators then tried to replicate the rod sticking with another H160 by leaving on the RH MGB fixed cowling and found that the “rod blocked further rotation” of the rotor blades. Further examination of the damaged helicopter showed that there were touch-up paint and marks on the RH MGB cowling and “marks on the pitch horn of the white blade that were consistent with an interaction with the pitch change rod.”

In a LinkedIn post around February 10, Duncan Moore, group chief safety officer for Omni Helicopters, issued a statement:

“In line with Omni’s commitment to transparency, this morning, I participated alongside Airbus Helicopters in a 200+ stakeholder call to update the operating community about the ongoing investigation into Omni’s recent H160 event.

“I’ve been around enough accidents and incidents now to know that every operator, everywhere, is capable of encountering circumstances that cause barriers to lose effectiveness. Omni is no different, and whilst the investigation is not complete, it is clear human factors play a potentially significant part in this event.

“The investigation team is now examining all of these aspects, and we are keen to find out more so that we can learn and share lessons, and act upon relevant findings for the organization. We commit to keeping all stakeholders informed so that together, we can continue to strive for a safer front line.

“Finally, thank you to both Cenipa and Airbus Helicopters for a simply outstanding collaboration, leading to one of the fastest-moving investigations we’ve seen in the sector. Best practice in action.”

Commenters on the post praised Moore for Omni’s transparency, commitment to learning, and for helping other H160 operators.