The circumstances surrounding a mishap involving a Lockheed Martin-owned F-35B Joint Strike Fighter last week, in which a still unnamed U.S. Air Force pilot at the controls at the time was able to safely eject and suffered no serious injuries, remain under investigation. However, the incident, dramatic video footage of which was captured at the time, makes it worthwhile to discuss an obscure feature on the aircraft: an 'auto eject' system that can engage the jet's Martin-Baker US16E ejection seat without direction under very particular circumstances.
The F-35B was conducting a test flight ahead of its formal delivery when the accident happened on December 15. The incident occurred at Naval Air Station Joint Reserve Base Fort Worth in Texas. Lockheed Martin's main F-35 production facility in Fort Worth shares a runway with this base.
The footage of the mishap, seen above, starts by showing the F-35B hovering. The B variant of the F-35, which is currently in service with the U.S. Marine Corps, Britain's Royal Air Force (RAF), and the Italian armed forces, is short take-off and vertical landing-capable.
As the video continues, the aircraft drops vertically at a relatively high rate. It then touches down briefly, bounces back up into the air, abruptly pitches forward, and comes down again, hitting the runway nose first. The hard impact leads to the jet's nose gear breaking off completely. At this point, power is not cut and the aircraft is propelled forward. The F-35B whipsaws back and forth as it spins out onto the adjacent grass and digs in on one side. The pilot is then seen ejecting while the aircraft is still in motion. A major fear in such circumstances relates to the aircraft rolling over, thus preventing a safe ejection.
The incident had already highlighted the so-called "zero-zero" capabilities of the US16E ejection seat, which refers to its ability to safely function and save the pilot's life even when the aircraft it is installed on is without forward airspeed or altitude, even as the aircraft is sitting stationary on the ground.
It is unclear whether or not the aircraft's auto-eject system was triggered during the December 15 incident. The War Zone reached out to Lockheed Martin for more information. A representative for the company subsequently directed us to contact the U.S. military's F-35 Joint Program Office (JPO), currently overseen by the U.S. Navy's Naval Air Systems Command (NAVAIR), and Martin-Baker, US16E ejection seat's manufacturer. The War Zone has reached out to both of those entities for additional details about this incident and the auto-eject feature more generally.
Though not regularly discussed, the existence of the auto-eject capability is no secret, even being listed among the US16E's features on Martin-Baker's website. The F-35B is the only version of the Joint Strike Fighter to have this system and is the first U.S. aircraft of any kind with such a capability, according to past information released by the F-35 JPO.
The inclusion of the auto-eject system on the F-35B is tied directly to the complicated way in which the aircraft achieves vertical flight. Lift in the hover mode is provided by a large fan installed vertically in the center of the jet's fuselage and from the thrust from the jet's Pratt & Whitney F135 engine, which is diverted downward via an articulating exhaust nozzle. The engine provides direct power to the lift fan via a large drive shaft attached to a carbon clutch. All three main variants of the F-35 are substantially different from each other in various ways, but the B version is especially so, right down to its core structure, due to this unique propulsion arrangement, as you can read more about here.
"Why do we need auto-eject? There's no auto-eject on the Harrier and over the life of the Harrier we've had one or two engine problems, and it's sort of sunk into the sea or it's sunk into the ground, and the pilot has ejected," Graham Tomlinson, a test pilot with U.K.-headquartered BAE Systems who was involved in early F-35B flight testing, said during a talk hosted by the Royal Aeronautical Society in 2020.
The F-35B replaced all versions of the Harrier jump jet, another vertical take-off and landing-capable combat jet, in RAF and Royal Navy service. It is slated to eventually fully take the place of the Harrier in the U.S. Marine Corps, as well.
"Why has the pilot usually been able to get away with it is because on the Harrier the thrust is central. There's one engine in the middle. The thrust comes out of four nozzles, more or less in the middle [of the aircraft]," Tomlinson continued. "So when the engine begins to cough and splutter, the thrust loss is sort of symmetric, it's near the center of gravity."
"On this thing [the F-35B], ... if you lose the core engine, you get an instant pitch up. If you lose the lift fan, you get an instant pitch down."
Tomlinson said that the possibility of a total sudden loss of thrust from the main engine is less pronounced given that inertia will keep the turbine spinning for at least some amount of time in many cases. How the lift fan works means that a failure there is much more dangerous, he explained, adding that simulations had shown an F-35B would end up flipping over nose down in less than two seconds if the drive shaft were to break during a hover.
This is "far too fast for any super-human test pilot or whatever to react [to]," according to Tomlinson. "There's no way you're going to react quickly enough to get out."
The exact mechanism or parameters by which the auto-eject system determines the aircraft to be outside of the pilot's control and triggers the ejection sequence is not clear. Nor is the exact status of it on the F-35B fleet. It is known that the US16E seats on all F-35 variants are otherwise linked to the aircraft's flight systems to help prevent the pilot from ejecting in unsafe conditions.
Interestingly, the Soviet Yak-38 and Yak-141 jump jets developed during the Cold War had engine arrangements more in line with that of the F-35B, but with vertically-mounted jet engines instead of a lift fan in both cases, and also had auto-eject systems. As with the F-35B, this feature appears to have been included primarily due to the potential for sudden nose-down pitch if the lift engines failed.
It remains to be seen what the investigation ultimately determines the cause or causes of the December 15 mishap to have been, and whether it emerges that the auto-eject system on the F-35B came into play at all.
Regardless, the auto-eject capability is an interesting and relatively obscure feature on the B variant of the Joint Strike Fighter, apparently made necessary by the jet's already unique means of hovering in mid-air.
Special thanks to Scott Lowe for reminding us of Graham Tomlinson's remarks about the auto-eject feature on the US16E ejection seat in the F-35B.
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