PACAF’s investigation found that hydraulic contaminated hydraulic fluid freezes and causes landing gear failure, causing Eielson AFB to lose the F-35A.
The Accident Investigation Board (AIB) report released by the PACAF on August 26, 2025 reveals what caused the situation Loss of US Air Force F-35A Lightning II On a training mission at Elson Air Force Base in Alaska on January 28, 2025. As we reported at the time, the plane crashed inside the fence of the base, and video showed the F-35 extending to the ground along its landing gear.
The aircraft was assigned to the 355th Fighter Squadron of the 354th Fighter Wing and was destroyed after a failed recovery attempt, although the pilot only ejected minor injuries safely. The total loss is estimated at $165 million, according to a press release on the investigation.
according to AIB official reportThe accident was triggered by hydraulic fluid contaminated with water, which freezes in cold Alaska temperatures and prevents proper extension of the landing gear. This failure triggered a series of events that ultimately left the aircraft uncontrollable and led to the crash.
Takeoff and preliminary failure
The accident occurred before 1 pm local time during routine training. After takeoff, the pilot tried to retract the landing gear, but the nose landing gear (NLG) failed to align and remained inclined between 17 and 25 degrees on the left. This irregularity was quickly diagnosed as a malfunction, and the pilot troubleshooted the problem with the assistance of the Flight Supervisor (SOF) and Lockheed Martin engineers and contacted by phone.
At that time, the temperature was Alson Well below freezing point – the observed temperature is -17°C (1.4°F), and the aircraft has spent considerable time exposed to the cold during pre-flight inspections. As AIB later determined, these conditions play a central role in failure.
Try the latest landing gear attempt
To correct the problem, the pilot is advised to implement it Touch and actTo help re-adjust the landing gear. On the first attempt, the nose gear failed to come soon. The second flight at a higher speed partially improved the situation, reducing the distance angle to about 6 degrees.
However, the ice accumulation in the main landing gear support rods prevents them from fully extending. As a result, the aircraft’s weight wheel (WOW) sensor mistakenly registered the jet on the ground, even if it was airborne. This sensor error causes the flight control system to switch to the “ground” flight control method, seriously undermining the jet’s handling.
The pilot suddenly experienced useless yaw and pitch oscillation. As the aircraft quickly becomes uncontrollable, assuming the attitude is 30-40 degrees, only 372 feet from the ground, the speed is 38 degrees, and the speed is 222 knots, then The pilot initiated a ejection. The escape system works as designed and the pilot lands safely nearby.
Aircraft loss and immediate response
A moment after ejection F-35A Stagnated at a height of 2,665 feet of AGL, spiraled out of control and hit the ground with a 116-degree right bank around Elson Air Force Base, thus being destroyed by the crash and subsequent fire. The AIB reported that emergency responders were on the scene within a minute.
Although the accident represents a significant material loss, it does not harm essential personnel or civilians. The service said the destroyed aircraft serial numbers are 1.9-5535 and are worth $165 million.
Root Cause Analysis
AIB determines the root cause of the crash Hydraulic fluid Contaminated by water, freezes in extreme cold and prevents the landing gear from being fully extended. Because the landing gear cannot sit properly in place, the system transmits false signals to the aircraft weight on the wheel sensor, resulting in wrong ground mode activation.
Investigate defects in the return of pollutants to maintenance and hazardous materials (Hazmat) management, especially inadequate sidewalks and frequent supervision changes. According to the report, hydraulic services were conducted in Eielson, with improper procedures.
Due to the limitations of equipment, maintenance personnel use less liquid than using a trolley instead of a nitrogen garment trolley, and the lines are not flushed adequately. As the AIB determined that the water was already in the support pole before the repairs three days before the unfortunate accident, water pollution inside the system was already in the support pole.
In addition, the hydraulic fluid barrel is not properly stored or tracked, and insufficient staffing and supervision can lead to this problem. The AIB stressed that these failures create an environment in which water seeps into the hydraulic system may not be detected.
Decision-making and human factors
Although technical failures are the direct cause of the accident, AIB also points to its contribution Human factors. Specifically, despite the high praise of all relevant efforts, the decision to continue troubleshooting of airborne problems has been questioned.
However, the board found that attempts to mechanically mechanically have a persistence of a new landing gear, rather than preparing for an emergency landing with misaligned gears, increased the possibility of catastrophic failures. In fact, the report mentioned that the Lockheed Martin maintenance circular began in April 2024, pointing out that WOW sensor issues may cause aircraft controllability issues and may be recommended for pilots to conduct planned full stop landings or Controlled ejection Instead of a second touch.
That being said, the report stressed that the pilot is a fully qualified and experienced F-35A evaluator pilot with a total of more than 2,700 hours, including 555 hours for the F-35A. The pilot also received a “Commended” rating in the fields of flight leadership and lecturer performance to demonstrate outstanding skills and knowledge.
Similar events
The January 28 crash was not an isolated case. Just nine days later, on February 6, another F-35A experienced comparable nose gear failure. In this case, the pilot received an insecure instruction after takeoff, lowering the landing gear for about 40 minutes before landing inconspicuously.
The report shows that the unsafe nose gear indication is due to the lack of the roller of the landing fluid and rotated 10 degrees to the left nose wheel in a similar manner as the crashed aircraft. In addition, on touchdown, the landing front wheels range from 10 degrees to left to 5 degrees.
Then, ground tests confirmed that frozen hydraulic fluid contamination is again caused. The report concluded that water might have existed on previous flights, but due to the high temperature and the water has no time to freeze, there has been no malfunction.
