A strange incident caused severe damage to a US Marine Corps (USMC) F-35B Lightning II stealth fighter on March 12th. During an overnight close air (CAS) training at Yuma Range in Arizona, a shell exploded shortly after being fired by the fighter.
The incident was categorized as a “Class A Incident” by USMC Captain Andrew Wood. As explained by the website The War Zone | The Drive, Class A incidents are the most serious in the classification used by the US. Episodes of this type involve damages in excess of $2.5 million, total loss of an aircraft, and the death or permanent disability of one or more individuals.
The Captain also highlighted that there were no injuries in the incident. The pilot managed to get the aircraft back to the base safely.
So far, what is known is that a PGU-32 caliber 25mm ammunition of type SAPHEI-T (Semi-Armor-piercing High-Explosive Incendiary-Tracer) exploded shortly after being fired by the GAU-22/A cannon loaded in the GPU-9/A pod, installed in the center of the fifth-generation fighter's fuselage.
When the PGU32 hits the target, a detonator triggers a slight delay device in the nose of the projectile, which then fires an incendiary element and a small explosive charge. The explosion also scatters a small amount of Zirconium, an element that burns at high temperatures when in with air.
In the video below, starting at 01:10, it is possible to see an F-35B firing the cannon during operations off the coast of Somalia.
The B (vertical landing and takeoff) and C (carrier catapult operations and cable recovery) versions of the F-35 Lightning II carry the GAU-22/A cannon in the GPU-9/A pod, while that the same gun is mounted internally in the F-35A variant, with conventional take-off and landing.
It is not yet known how the ammunition detonated in this way, which is expected to be revealed by the ongoing investigation.
The F-35 incident may be reminiscent of another incident in 1956 with a Grumman F11F-1 Tiger fighter. In this case, Grumman test pilot Tom Attridge was conducting tests firing at supersonic speeds, employing the four Colt Mk.12 20mm guns.
At 20 feet, already at Mach 1, Attridge entered a 20º dive and gusted. At 13 feet he fired again and continued to dive, this time at a steeper angle. At seven thousand feet the plane collided with some small objects, suffering loss of engine power and damage to the windshield.
Attridge thought he had collided with birds, and reported to the tower that his engine was only generating 78% of power and that the windshield and right side air intake nozzle were badly damaged.
On approach for landing, the fighter was not responding well at 78% power. Attridge accelerated, but the engine died completely. The plane crashed near the runway, lost its right wing and caught fire. Attridge, despite being injured, survived the violent crash and returned to flying six months later.
During the investigation it was discovered that the objects were actually 20mm projectiles, the same ones fired by Attridge moments before. The F11 ran over the ammunition. While the projectiles were decelerating due to friction and the ballistic trajectory, the fighter continued to accelerate, which caused the “encounter” at a given moment in the flight.
Via The War Zone, Military.com
