Fighter Planes Shooting Themselves Down

Son, I’m sorry, they got us.

— Henry Jones, Sr.

If Indiana Jones and the Last Crusade can serve as a real-world guide, the perils of a dogfighter circa World War II stretched beyond incoming fire from the enemy. Gunners had to make sure they didn’t imperil their own craft, too.

More modern (and non-Hollywood) airplanes avoid the pitfalls facing Sean Connery in the film by not pointing at their own parts. The stereotypical fighter jet features guns and missiles that exit from fixed barrels, pointing forward. Projectiles emerging from a plane in flight offer an interesting example of frames of reference or basic relativity.

If a human shoots a gun and the bullet leaves the gun at 1,000 miles per hour, the speed of the bullet is straightforward. How fast would the bullet travel if it were mounted to an airplane also flying at 1,000 miles per hour? To the pilot, the bullet would appear to move at a rate of 1,000 miles per hour. However, to a person on the ground, the projectile would move at 2,000 miles per hour. Both frames of reference would watch the bullet move away from the craft at 1,000 miles per hour.

In such a scenario, one might conclude the plane would never face any danger of running into its own bullet. However, this assumption neglects a few factors.

Our scenario holds in a vacuum, but we know the planet is full of atmosphere. Air is not frictionless. As soon as a bullet leaves a barrel, it begins to slow thanks to drag. The airplane can overcome drag to maintain its speed thanks to its jets, which require fuel. So, theoretically, the plane might remain in motion at 1,000 miles per hour, while the bullet slows, potentially to the point where it travels at less than 1,000 miles per hour. Could the plane ever catch the bullet?

Again, this question omits an important element. We have only considered horizontal motion. Under the influence of gravity, projectiles move in vectors horizontally and vertically. When a bullet leaves a barrel, gravity immediately begins to pull it toward Earth. The result of its horizontal movement, thanks to the firing mechanism, and its gravitational movement create an arc. The following graph displays a skydiver leaving an airplane at different speeds, but the motion would be the same for a horizontal bullet.

So, even if an airplane could manage to catch up to the decelerating bullet, the craft would never intersect its own projectile on a gravitational body. The bullet will have descended below the impact point.

What if the gun were not pointed horizontally, but slightly upward? In this scenario, we get the traditional, parabolic projectile arc.

If the barrel were angled upward, could a plane fly fast enough to catch up to the trajectory of the bullet so they intersected as it began to move downward?

Theoretically, a jet might be able to accelerate significantly after firing a projectile to make this potentiality occur. However, as you might have guessed, based on real-world inputs, this scenario does not transpire. Crafts do not speed up after firing and, more importantly, gravity is such a huge factor that bullets would drop too much, even if the planes did gather enough speed.

Ergo, we can conclude that fighter planes cannot shoot themselves down, short of some sort of Indiana Jones mistake or heat-seeking missile malfunction. Right?

Wrong!

Once again, we overlooked an aspect. On 21 1956, a Grumman F-11 Tiger fulfilled all the necessary ingredients, becoming the first fighter plane to shoot itself down.

Mounted with 20-millimeter cannons, pilot Tom Attridge took a Tiger to the skies to test the weapons of the new planes. Partway through a shallow dive, Attridge blasted two bursts from the cannons. Shortly afterward, the pilot needed to make a crash landing, after what he thought was a bird strike. Attridge suffered a broken leg and broken vertebrae but survived. Upon inspection of the wreckage, the Navy discovered 20-millimeter holes.

Attridge had shot himself down.

The secret sauce to this scenario was the downward motion of the plane. The drag on the bullets transpired as usual, but, after firing, Attridge dived steeply, which allowed the craft to intersect the projectiles as they slowed.

The Navy evaluated the situation as a fluke, but Attridge correctly figured it could happen to any fast plane. In 1973, a pilot flying an F-14 Tomcat was struck by his own missile, which was thankfully a dummy. In 2019, a pilot in the Netherlands repeated the 20 mm feat in an F-16 but was able to land safely.

As engineers have designed planes to become faster and faster, the possibility of shooting one’s self down has only increased. However, most fighter planes have moved away from mounted guns and toward missiles that are guided automatically by computers or remotely, which greatly diminishes the chances of impact with the original craft.

Though these scenarios do not rely on the magic of general relativity’s time travel, they remind me of the grandfather paradox. In this thought experiment, one travels backward in time and kills one’s own grandparent. What would happen? Would the time traveler cease to exist? Causality and the flow of time pose major problems with how we perceive the universe. Usually, these notions require moving at close to the speed of light, a wormhole, futuristic technology, or all three. As it turns out, without any physics loopholes, one can approximate this paradox with everyday mechanics!

Henry Jones, Sr., thought he had to blame the Nazis for shooting their airplane in Last Crusade. Had the setting been a few decades later, he might have been aware of planes being able to shoot themselves down and he could have blamed his son!