Accident Summary
On 29 November 2023, at approximately 1440 local time, a CV-22B Osprey (tail number 10-0054) crashed into the water about half a mile off the coast of Yakushima Island, Japan. The aircraft was participating in a joint interoperability exercise and was operated by the 21st Special Operations Squadron, 353rd Special Operations Wing, Yokota Air Base, Japan. The eight crew members included five CV-22B aircrew from the 21st SOS, one Direct Support Operator from the 43rd Intelligence Squadron, and two medical personnel from the 1st Special Operations Squadron. The aircraft was destroyed, and all crew members sustained fatal injuries upon impact. Seven crew members were recovered during search and recovery operations; the eighth was not found despite an extensive 43-day multinational search.
Sequence of Events
The mishap crew aborted their planned mission after receiving multiple advisories and a caution indicating a "Land as Soon as Possible" condition in the cockpit. They diverted toward Yakushima Airport, approximately 60 miles east of their position. While on final approach at about 800 feet above ground level, the aircraft experienced a sudden materiel failure that initiated an immediate left roll, causing the aircraft to roll twice before impacting the water.
Findings
The Accident Investigation Board determined that the mishap was caused by a catastrophic failure of the left-hand Proprotor Gearbox. This failure led to a rapidly cascading failure of the aircraft's drive system, resulting in an instantaneous asymmetric lift condition that the crew could not recover from. Additionally, the board found that the Mishap Pilot's decisions were causal, as they prolonged the mishap sequence and eliminated any consideration of an earlier landing at a different divert location. The board also identified two contributing factors: inadequate risk management and ineffective crew resource management, which together resulted in an insufficient sense of urgency throughout the mishap sequence, beginning with the first proprotor gearbox cockpit advisory approximately 49 minutes before impact.