In 2019, a Japanese F-35A crashed into the sea during a training flight. Detailed analysis of the pilot’s spatial disorientation and technological limitations.
Summary
On April 9, 2019, a Japan Air Self-Defense Force F-35A Lightning II disappeared into the Pacific Ocean, approximately 135 km east of Misawa, in northern Japan. Engaged in a night training flight with three other aircraft, the plane left formation and crashed into the ocean at high speed. The pilot, Major Akinori Hosomi, 41, had logged more than 3,200 flight hours, including only about 60 on the F-35. The investigation concluded that the pilot had suffered spatial disorientation: he was no longer able to correctly perceive the attitude of his aircraft and plunged into the sea without realizing it. No distress message was sent, and no attempt to eject was observed. This tragedy highlights an uncomfortable reality: an ultra-connected 5th generation fighter jet equipped with sophisticated sensors is not enough to eliminate the risk of F-35 accidents in Japan linked to human error. Safety still depends, first and foremost, on training, procedures, and anticipating human limitations.
The context of a training flight on a 5th generation fighter
The F-35A involved is 79-8705, the first aircraft assembled in Japan by Mitsubishi in Nagoya. It had accumulated approximately 280 flight hours at the time of the accident. On April 9, 2019, four F-35As took off from Misawa for night air combat training over the Pacific. After about 28 minutes of flight, Major Hosomi’s aircraft disappeared from radar screens.
The flight took place at high altitude, in a dark environment, with no visual reference points on the ground. On a clear but dark night, the Pacific blends into the sky. The F-35A is then flying in a mode where the pilot relies almost entirely on his instruments to know the aircraft’s attitude.
In the Japanese Air Self-Defense Force, the integration of the F-35 is still recent. The pilots come from other platforms, notably the F-15J and F-4EJ Kai. They are discovering a radically different cockpit: a single large screen display, HMDS helmet projecting information directly in front of their eyes, data fusion. This modernity provides a wealth of information, but also a risk of cognitive overload, especially at night and during tactical exercises.
The precise chronology of a crash at sea
Flight data reconstructed by the Japanese authorities provide a precise scenario. The F-35A is participating in a simulated combat exercise. To create distance from another aircraft, Major Hosomi initiates a left turn in a controlled descent. The aircraft transitions from stable flight to a downward trajectory with a negative attitude.
Halfway through the maneuver, the pilot announced “knock it off,” which means to stop the exercise. The radio transmission revealed no stress or particular difficulty. The tone was calm. However, the aircraft’s trajectory remained in descent. Speed increased and altitude decreased. The parameters show a drop of more than 300 m per second, or more than 1,000 ft/s, from an altitude of less than 4,900 m (16,000 ft). The time available to react is then around 15 to 16 seconds.
No recovery maneuvers were recorded. No distress call was made. The aircraft struck the ocean surface at high speed, almost in line with its flight path. Debris was later found on the seabed, at a depth of approximately 1,500 m, scattered over a wide area. The ejection seat was not activated.
This profile—high-speed impact, no attempt to eject, aircraft in flight—is typical of a case of controlled flight into terrain, or CFIT, in this case into the sea.
Spatial disorientation, an invisible enemy for pilots
Spatial disorientation refers to a pilot’s inability to correctly perceive the position, attitude, or trajectory of their aircraft in relation to the horizon. In a 5th generation fighter jet cockpit, the human body remains subject to the same physiological limitations as in an older aircraft.
At night, over the sea, with no visible horizon, the inner ear and vestibular system often send misleading signals. During a prolonged descent and stabilized turn, the pilot may feel as if they are flying horizontally. Conversely, a return to normal attitude may be perceived as an excessive climb or bank.
In this specific case, the investigation concluded that Major Hosomi probably lost his perception of the aircraft’s actual descent. He believed he was in control, when in fact the aircraft was heading towards the sea at high speed. The on-board instruments, however, provided the correct information. But if the pilot does not consult them sufficiently, or if he trusts his senses more than the instruments, sensory illusion prevails.
This type of accident is not specific to the F-35. Other fighter jets have been lost in similar circumstances: an American F-16 in Michigan in 2020, F/A-18s, military helicopters. In military aviation, spatial disorientation remains one of the leading causes of fatal accidents in flight, especially at night or in poor weather conditions.
Human factors specific to the pilot and the Japanese fleet
The pilot’s profile raises questions. With 3,200 flight hours, Major Hosomi is an experienced officer. However, he has only logged about 60 hours on the F-35A Lightning II. He is still learning about a new aircraft, with flight sensations, cockpit ergonomics, and automatic systems specific to this model.
The transition from an older aircraft to a fifth-generation fighter is not just a question of technology. It requires breaking down habits and reflexes acquired over thousands of hours in order to adopt new visual and mental reference points. In the first few months, pilots navigate a gray area: generally experienced, but relatively new to their new aircraft.
The operational context also weighs heavily. The F-35 is a powerful political symbol in Japan. It embodies the modernization of defense against China and North Korea. The pilots selected for conversion to the F-35 know that they are carrying out a strategic program. The pressure to perform may be subtle, but it is real.
The investigation also highlights the workload during flight: tactical exercises, radio coordination, radar and sensor management, and monitoring the training scenario. In this context, the pilot may devote less attention to fine control of the aircraft’s attitude, especially if the flight appears to be under control. The pilot’s disorientation then sets in silently in the background, until the point of no return.
The limits of technology in the face of spatial disorientation
On paper, the F-35 combines systems designed to enhance flight safety: multiple sensors, data fusion, sophisticated displays, and decision support. However, none of these technologies prevented this F-35 accident in Japan.
There are several reasons for this apparent paradox. First, not all warning systems are equivalent. Modern airliners have highly intrusive TAWS/EGPWS (Terrain Awareness and Warning System) systems, which trigger repeated audible alarms and impose immediate resource procedures. On a fighter jet, the logic is more nuanced: the aircraft must be able to fly low, fast, and sometimes very close to the ground. An alarm that sounds too frequently would be unusable in operation.
Furthermore, at the time of the accident, according to open sources, the Japanese F-35 did not yet have the operational version of Auto-GCAS, the automatic ground collision avoidance system. This software, already operational on the F-16, takes control of the aircraft in the event of a trajectory deemed incompatible with survival, if the pilot does not react. Its integration into the F-35 fleet was accelerated from mid-2019, precisely to reduce the risk of CFIT.
Finally, technology only makes sense if the pilot listens to it. Warning systems can issue messages about attitude or rate of descent. But if the pilot is convinced that they are in a different situation, or if they misinterpret the indications, the alarm may be ignored, downplayed, or read too late.
The heart of the problem therefore remains the “human link.” Sophisticated technology cannot compensate for a loss of situational awareness, especially when it occurs in a matter of seconds.
Possible responses: training, procedures, and backup systems
After the accident, the Japanese authorities took several measures. F-35 flights were temporarily suspended while the fleet was inspected to ensure that no mechanical faults were involved. The official conclusion ruling out mechanical failure reinforced the confidence of other user countries, but refocused the debate on human factors.
Japan is stepping up training in spatial disorientation. F-35 pilots are receiving more simulator sessions, with scenarios reproducing the sensory illusions encountered at night, during turns or during prolonged descents. The goal is to condition reflexes: when in doubt, immediately return to the instruments, make a recovery, stabilize the flight, and only then resume the tactical exercise.
Training procedures are also being reviewed. Altitude, descent rate, and speed limits for night exercises are being clarified. Patrol leaders must monitor the trajectories of their wingmen more closely in order to detect abnormal descent earlier.
Finally, the acceleration of the integration of Auto-GCAS on the F-35, decided at the international level, is a strong technological response. This system, which has already been credited with several “rescues” on F-16s, is designed to take control when an aircraft approaches the ground without an adequate response from the pilot. It does not eliminate the risk of spatial disorientation, but it does offer a last barrier against impact.
Lessons learned for the integration of 5th generation fighters
This accident highlights an often underestimated reality: a 5th generation fighter is not just a technological leap forward, it is a change in operational culture. Forces adopting platforms such as the F-35 must adapt their training methods, employment doctrines, and approach to the human factor.
The Misawa F-35A incident serves as a reminder that most serious accidents are not caused by spectacular machine failure, but by a series of micro-errors, misperceptions, and ignored signals. The more complex the aircraft, the narrower the margin between mastery and cognitive overload.
The next step for the air force will be to combine three levels of protection: pilots who are better prepared for sensory illusions, more robust training procedures, and automatic systems such as Auto-GCAS that are capable of correcting the irreparable. The 2019 tragedy claimed the life of an experienced pilot and destroyed a strategic aircraft. It also served as a catalyst for a concrete rethinking of how to integrate the new F-35 Lightning II into national fleets that remain, above all, human.
Sources
- Japan Air Self-Defense Force and Ministry of Defense, summary of the investigation into the F-35A accident on April 9, 2019.
- Reuters, “Japan’s military says pilot vertigo likely cause of F-35 crash,” June 10, 2019.
- The Aviationist, “Pilot’s Spatial Disorientation The ‘Likely’ Cause Of Last April’s Japanese F-35 Jet Crash,” June 11, 2019.
- National Interest, “Exposed: How a Japanese F-35 Crashed During a Combat Exercise,” June 15, 2019.
- Aviation Safety Network, Lockheed Martin F-35A Lightning II 79-8705 accident report, Misawa, 2019.
- AFRL, Lockheed Martin, and public documentation on the Automatic Ground Collision Avoidance System (Auto-GCAS) and its integration into the F-35.
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