A US F-35B caught fire on October 17, 2025, while landing in Iwakuni. This incident highlights the technical challenges of STOVL engines and weighs on Indo-Pacific deployment.
Summary
On October 17, 2025, during a joint exercise with the Japanese Self-Defense Forces at Iwakuni Air Base, a Marine Corps F-35B Lightning II suffered a major fire during a vertical landing maneuver. No injuries were reported, but the event raises crucial questions: the operation and robustness of STOVL (Short Take-Off / Vertical Landing) engines, the risks associated with daily use in sensitive operational areas, and the impact on customer confidence, sales, and the Indo-Pacific deployment schedule. The F-35B employs a complex architecture—main engine with swivel nozzle, lift fan, tilt system—making it sensitive to thermal, hydraulic, or flow failures. While the investigation will determine the cause, this incident could slow expansion plans, delay certain deliveries, or prompt potential customers to turn to STOL or conventional alternatives.
The incident at Iwakuni: sequence of events and context
The event
During a bilateral exercise between the US Marines and the Japanese Forces, an F-35B performing a vertical landing (hover + vertical descent) at Iwakuni Air Base caused a major fire. The aircraft had already been in vertical approach or transition to landing. The fire broke out during or immediately after contact with the platform. The pilot ejected or evacuated without major injury, and rescue teams extinguished the fire.
So far, no official statement has been released giving the precise cause, but the incident is being treated as serious, particularly because a fire in the engine or lift nacelle area carries a high risk of structural damage.
Geographical and strategic issues
The Iwakuni base is a key location for the US posture in the Indo-Pacific region. It is home to forward-deployed F-35B squadrons, ready to project power into the contested waters of the East or South China Sea. If the STOVL fleet shows vulnerabilities, this could delay expansion plans in the Philippines, Taiwan, or forward bases.
This incident comes amid regional escalation with China, which is strengthening its naval fleet, anti-ship missiles, and coastal defense systems. The effectiveness and reliability of the F-35B are therefore crucial to maintaining US air and naval deterrence.
The F-35B’s STOVL engine: complexity and risks
STOVL engine architecture
The F-35B combines several subsystems to achieve STOVL flight:
- An F135 (STOVL version) main engine with a rear vectored thrust nozzle that can tilt downward (vectoring) to generate vertical thrust.
- A lift fan located at the front of the fuselage, driven by the main engine shaft via a transmission shaft, providing downward thrust at the front to balance the aircraft in vertical mode.
- Flow diversion doors (ducts) and flaps to manage the transition from horizontal to vertical flight, distribute flow, and prevent hot recirculation.
- A thrust control, hydraulic, and digital control system that coordinates the complex task of thrust direction and balancing.
This architecture presents constraints in terms of thermal, airflow, synchronization, vibration, and material robustness.
Possible causes of fire in the STOVL zone
Several scenarios can trigger a fire in this configuration:
- Seal failure or structural break in the hot flow ducts, causing hot gases to leak onto flammable surfaces.
- Hydraulic or control problems (vector control channels, flaps) preventing proper flow distribution and creating turbulence or recirculation that heats unintended areas.
- Contamination or obstruction in the intake, bleed, or cooling ducts, causing local overheating.
- Failure of the starting system, lubrication or ignition product in areas close to the main engine or lift compartment.
- Thermal interaction between hot engine flow directed towards unprotected parts, or projection of burning material when the nozzle tilts, affecting cables, hoses or peripheral circuits.
- Wear, corrosion, fatigue, or material defects on critical components: ducts, flanges, joints, shaft segments.
Without a public investigation, no hypothesis can be favored. But engine fires in F-35Bs are not entirely unknown: in 2016, an F-35B experienced a fire in its weapons bay during a training mission.
Impact on the engine, airframe, and integrity
A fire can damage:
- The airframe structure around ducts, panels, reinforcements, and cooling ducts.
- Hydraulic circuits, cables, and electrical harnesses in the fire zone.
- The engine itself: turbomachinery, thermal coatings, injectors, blades, and seals.
- The lift fan and transmission mechanisms may suffer thermal or mechanical overload.
- Stealth surfaces (radar-absorbing coatings) may be damaged, altering the aircraft’s radar signature.
Depending on the extent of the damage, the aircraft may be repairable, but this requires thorough inspections, module replacements, non-destructive testing, and post-repair validation.
Perception, sales, and implications for deployment
Effect on customer confidence and commercial image
The F-35, already the subject of criticism regarding costs, maintenance, and technical problems, may suffer from this incident in public opinion or among customer countries. Countries in the evaluation phase (e.g., Singapore, Switzerland, India, South Korea) could use this episode to argue in favor of alternative options (Eurofighter, Rafale, Su-57, indigenous aircraft).
Current or future contracts could be delayed or renegotiated, particularly if availability, reliability, or safety requirements are tightened.
Repercussions on the Indo-Pacific timetable
Any temporary suspension of F-35B flights or fleet inspection could delay the advanced posture in the Pacific. Deployed units could be resized, or certain STOVL missions reassigned to runway-based aircraft.
If the technical problem is deemed systemic or recurring, the USMC could slow down STOVL capacity expansions at forward bases or helicopter carriers converted for F-35Bs (the “Lightning carriers” concept).
Adjustments in maintenance and quality services
Lockheed Martin, Pratt & Whitney, and the Pentagon will need to strengthen quality controls, introduce enhanced mechanical inspections, analyze failure modes, and introduce corrective hardware or software modifications.
Each major incident often leads to technical advisory bulletins (TACs), supplier returns, temporary sample shutdowns, and software or hardware updates to prevent recurrence.
Previous examples and reliability history
The history of the F-35B already includes several incidents: emergency landings, precautionary landings, and electrical failures. In December 2022, an F-35B’s nose gear collapsed while taxiing after an emergency landing in Okinawa.
Another instructive case: a fire in the bomb bay of an F-35B in 2016 led to an investigation into the compartmentalization concept and thermal protection. This history shows that the program has already had to deal with unforeseen events—but a fire during hovering/vertical landing is more critical because it affects the most vulnerable configuration of the system.
Outlook for the investigation, risk, and lessons learned
Technical investigation and expected analyses
The investigation will need to collect data from black boxes (flight data recorder, health monitoring), combustion traces, metal residues, thermal readings, and IR and optical images.
Engine, structural, hydraulic, and control experts will have to reconstruct the chronology: ignition of the fire, its spread, and the response of the safety systems.
The investigation will also have to verify whether the control software responded correctly, whether previous alerts had been ignored, or whether previous maintenance had introduced a weakness.
When will recalibration take place?
If the incident is isolated, corrective modifications (reinforced seals, heat insulation, modified segments) can be incorporated into the maintenance program.
If a structural or design flaw is found, this could lead to a temporary halt in flight cycles for inspection of the entire STOVL fleet, or a partial withdrawal until upgrades are made.
Lessons for other STOVL programs
The challenges facing the F-35B are not insignificant: any future STOVL fighter or “stealth naval F-35” program will need to incorporate enhanced safety margins, thermal redundancies, and increased fire protection in vertical/normal transition areas.
Less extreme STOL (Short Take-Off/Landing) alternatives could become more attractive if the risks of STOVL are deemed too difficult to manage.
This spectacular fire in Iwakuni is a stark reminder that STOVL designs, as bold as they are, involve extreme technical challenges. While the F-35B remains a key component of US air power projection in contested maritime areas, its reliability must be beyond question in order to inspire confidence. At a time when China is accelerating its naval development, the USMC must ensure that its aircraft can operate safely and continuously, without critical failures undermining their role as a strategic spearhead.
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