A detailed look at the accident and lessons learned from the December 2023 U.S. F-16 crash near Kunsan AB.
On Dec. 11, 2023, at around 08:42 local time, a pilot assigned to the 35th Fighter Squadron of the 8th Fighter Wing at Kunsan Air Base in the Republic of Korea, ejected without injury from the F-16CM aircraft tail number 88-0479, the number 3 in a formation of four F-16s flying as SOMAEK 11 – 14.
The aircraft, radio callsign SOMAEK 13, assigned to the 80th Fighter Generation Squadron (FGS), crashed into the Yellow Sea. approximately 81 nautical miles west of Kunsan Air Base, resulting in its total destruction. The mishap led to the loss of a U.S. Air Force asset valued at $28,259,045.00.
According to the Accident Investigation Board report, the crash was caused by critical failures in the jet’s primary flight and navigation systems: at approximately 08:37 local time, while flying through clouds in instrument meteorological conditions (IMC), the pilot lost the use of the primary instrument that indicates the aircraft’s position relative to the horizon, known as the attitude indicator. This instrument relies on data from an Embedded GPS/INS system (EGI), which failed during the flight. The pilot quickly switched to the standby attitude indicator (SAI), the only remaining source of attitude information. However, the pilot had earlier noticed minor pitch and bank inaccuracies on the SAI, making it harder to reconcile its readings with the aircraft’s speed and attitude, further worsening spatial disorientation.
With assistance from a wingman flying behind and relaying navigation and altitude data, the pilot began descending in search of clearer skies, as anticipated from the pre-flight weather briefing. Still flying in IMC at 3,000 feet mean sea level (MSL), the pilot attempted to level off but became increasingly disoriented. As the aircraft neared the water and confidence in its attitude readings diminished, at an altitude of 1,730 feet above sea level, the pilot ultimately decided to eject.
The investigation board identified the primary cause of the mishap in the EGI failure while flying in IMC, which led to the loss of essential flight and navigation instruments. Additionally, the pilot’s subsequent reliance on the SAI, which had previously shown abnormal readings, contributed to the mishap.
The Incident: Technical Failures in Adverse Conditions
The aircraft was flying through dense cloud coverage when, approximately 13 minutes into the flight, its primary flight and navigation systems failed. In normal operations, the F-16C’s onboard GPS inertial navigation system (INS) plays a critical role, providing the pilot with accurate horizon and attitude information, which are crucial for maintaining aircraft control, especially in poor visibility.
However, on this flight, the INS malfunctioned, leaving the pilot with only a backup system: the standby attitude indicator. This backup device, which is designed to function in emergencies, was also experiencing significant errors, particularly in pitch and bank readings. The pilot faced conflicting information between the faulty standby indicator and the visual cues provided by a wingman, which only worsened the spatial disorientation.
Investigative Findings: A Focus on Instrument Failures
The Accident Investigation Board (AIB) meticulously examined the circumstances leading to the mishap. The board president concluded that the immediate cause of the crash was the failure of the aircraft’s EGI system, which caused the loss of critical flight and navigation data at a time when the pilot needed to rely on those instruments due to the adverse weather. The malfunction left the pilot in a precarious situation, dependent on the standby attitude indicator, which, as the investigation found, was providing inaccurate readings.
The AIB noted that without the GPS navigation system failure, the mishap likely could have been avoided. Although the pilot tried to navigate using information from the wingman, the discrepancies between the erroneous standby indicator and the external data led to severe spatial disorientation, a condition in which a pilot loses awareness of their aircraft’s position relative to the earth. The board also acknowledged that the total destruction of the F-16C significantly hampered efforts to fully analyze the malfunction, leaving some questions about the precise technical cause of the GPS/INS failure unanswered.
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Spatial disorientation
Spatial disorientation (SD) is a significant factor in aviation accidents, and NATO describes it as a failure to maintain spatial orientation (SO), a fundamental human behavior that integrates multiple sensory and motor systems in the brain. When SD occurs in a flight environment, it can have catastrophic consequences. Over the years, studies have attributed 25 to 35% of serious aviation accidents and 25 to 50% of fatalities to SD, a statistic that has remained consistent despite ongoing efforts to address the issue.
NATO refers to a widely accepted definition by Benson, which describes SD as a situation where “a pilot fails to sense correctly the position, motion, or attitude of himself or his aircraft within the fixed coordinate system provided by the surface of the earth and the gravitational vertical.” This definition emphasizes that SD doesn’t refer to simply getting lost, but includes scenarios where a pilot misjudges their aircraft’s position, such as impacting an object they were aware of but miscalculated.
Historically, terms like “aviator’s vertigo” or “pilot vertigo” were used to describe what is now known as SD. During World War II, the concept of “Loss of Situational Awareness” (LSA) emerged, which included disorientation and a lack of understanding of the pilot’s position. While SD and LSA are related, they aren’t identical—SD always involves LSA, but LSA can occur without SD. Efforts to mitigate the dangers of SD date back to the early days of aviation, with early countermeasures focusing on training rather than technical advancements.
Despite technological and procedural improvements, SD remains a persistent issue in aviation. As NATO underscores, SD represents a failure of pilots to accurately perceive their aircraft’s orientation relative to the earth, often leading to dangerous miscalculations that can result in accidents…
Safety Measures and Future Prevention
The findings from the F-16C crash investigation prompted the U.S. Air Force to take immediate steps to mitigate the risks associated with similar incidents. PACAF (Pacific Air Forces) launched a comprehensive safety investigation alongside the AIB’s legal inquiry, ensuring that lessons learned from this mishap were rapidly integrated into training and operational procedures across the Air Force.
Air Combat Command (ACC) introduced enhanced, continuous training for F-16 pilots, emphasizing the identification and correction of flight instrument malfunctions during emergency situations. This training underscores the critical role of understanding system limitations and recognizing when instruments may be providing inaccurate data. The Air Force also began working on solutions to minimize the impact of temporary power fluctuations on flight instruments, a potential contributing factor to the failure of the F-16’s EGI in this case.
