What happened
On 28 January 2025, an F-35A, tail number 19-5535, crashed at Eielson Air Force Base, Alaska, following a series of touch-and-go landings. The aircraft, operated by the 355th Fighter Squadron under the 354th Fighter Wing, was performing a training sortie when the pilot noticed the nose landing gear (NLG) door was ajar. Upon extending the gear, the pilot discovered the NLG wheel was canted approximately 17 degrees to the left.
Following an in-flight consultation with engineers via a conference call, the pilot attempted two touch-and-go landings to try and re-center the nose gear. During these maneuvers, ice formed within the landing gear struts. This prevented the right and then the left main landing gear (MLG) struts from fully extending. Consequently, the aircraft's Weight on Wheels (WoW) sensors incorrectly signaled that the aircraft was on the ground while it was still airborne. This caused the flight control laws to transition to an "on ground" mode, rendering the aircraft uncontrollable. The pilot successfully ejected, sustaining minor injuries, but the aircraft was destroyed, resulting in a loss valued at $19GT6,500,000.
The investigation
The Accident Investigation Board (AIB) examined the mechanical failures and maintenance history of the aircraft. Investigators looked into the hydraulic servicing procedures used by the 355th Fighter Squadron and the management of the unit's hazardous materials program. The board also reviewed the decision-making process during the in-flight emergency, including the communications between the pilot, air traffic controllers, and Lockheed Martin engineers.
Findings
- Hydraulic fluid contamination by water was the primary cause of the mishap. The water froze inside the NLG and MLG struts, preventing full extension.
- The frozen struts caused the WoW sensors to falsely indicate the aircraft was on the ground, triggering an inappropriate flight control law.
- Crew decision making during the in-flight conference call contributed to the accident, as the decision to attempt further touch-and-go landings led to the loss of control.
- A lack of adherence to maintenance procedures for hydraulic servicing equipment was identified, specifically regarding how hydraulic barrels were stored and handled.
- Inadequate oversight of the squadron's hazardous materials (HAZMAT) program contributed to the presence of contaminated fluid in the system.