The crash of an Osprey jet off the coast of Japan last November, killing all eight service members on board, was caused by a “catastrophic failure” of the rotor gearbox and the pilot’s decision to continue flying despite multiple warnings to land, the ministry said. Air Force investigation It was announced on Thursday.
The Nov. 29 crash of a CV-22B Osprey off the coast of Yakushima was one of four fatal Osprey accidents in the past two years, leading to a military-wide grounding of the plane for months and sparking a major investigation into the incident.
Questions remain about whether the aircraft, which takes off and lands like a helicopter but flies like a plane, is safe and should be left for military use.
“By conducting a thorough review and accident and safety investigation, we hope to provide answers for the families of the Airmen who lost their lives and prevent future accidents and tragedies,” Lt. Gen. Tony Bauernfeind, former commander of Air Force Special Operations Command, who convened the accident investigation board into the incident, said in a statement.
An investigation determined that the accident was caused by “catastrophic failure of the left propeller rotor gearbox, causing rapid cascading failures of the aircraft’s drive system, resulting in the Osprey violently rolling over and crashing into the water.”
The crew’s decision-making also played a role in the crash, with the pilots being so “casual” during the military exercise that they “never considered landing earlier at an alternative diversion site,” the report said.
Despite these issues, V-22 Osprey officials knew that if a gearbox component failed “it could result in a total loss of the aircraft and crew,” lead investigator Lt. Gen. Michael Conley reportedly told media on Wednesday.Associated Press.
Conley also told the outlet he believes the pilots’ instinct to finish their training led them to not land sooner.
Additionally, the investigation found that the V-22 Osprey office did not share safety data that could have educated crews about how serious the risks of not landing were.
Specifically, the failure was caused by a key component of the propeller gearbox, a pinion gear. The box is the aircraft’s transmission and contains five pinion gears that spin to send energy from the engines to the Osprey’s mast and rotor blades. The Air Force does not yet know what caused the part to fail.
As the Osprey flew off the coast of Japan en route to Okinawa, it experienced two vibrations in the aircraft: one in the drive shaft connecting the plane’s two engines, followed by a vibration in one of the pinion gears.
The vibrations are considered a sign of a potential problem, but because such data can only be downloaded and examined at the end of a flight, the pilot, Maj. Jeff Horneman, and the crew were unaware that it was happening.
Horneman received six more warnings of impending impacts, such as metal fragments falling off the Osprey’s gear, and warned the pilots each time. Official guidance says pilots are instructed to “land as soon as possible” after three such incidents.
Investigators found that a decision not to land after every warning led to the crash.
According to a report obtained from the voice data recorder on the day of the accident, Horneman and the crew could not detect any other problems, such as overheating, so they instructed the co-pilot to monitor the situation and elected to continue the training at sea.
The Osprey also has a chip detector that burns off tiny metal pieces, preventing them from splattering into the oil and damaging the transmission.
Until the final minutes of the flight, Horneman was so focused on completing his training that he rejected his co-pilot’s suggestion to identify the closest airfield for landing.
After the sixth tip warning, there were indications that the Osprey could no longer burn tips and the plane should have landed “as soon as possible,” but the crew did not appear to take it as an emergency.
Conley told reporters that the Osprey gave a final warning of a “chip detector failure” three minutes before the crash, but that this was because the detector “had so many chips in it that it couldn’t respond.”
Horneman said he misinterpreted this and earlier warnings as errors caused by a faulty chip detector and wasn’t concerned.
Just before the crash, the Osprey was preparing to land and was just half a mile from an airfield on Yakushima Island, but postponed its landing after Japanese air traffic controllers told it to wait until local traffic had taken off.
Because the pinion gear had broken, Horneman instructed the co-pilot to “make another wide right turn and then prepare for landing.”
About six seconds after the rupture, the Osprey’s gear and interconnected drive system experienced a critical failure, causing the aircraft to crash, with the crew unable to do anything to save themselves or the aircraft, according to an investigation.
The accident led to several changes, including new instructions for pilots to land as soon as possible after the first tip burn, and again after the second. The Osprey program, which resumed operations last month, is also getting a new system that will transmit vibration data to pilots in real time.
