On September 21, 1956 Grumman test pilot Tom Attridge was shot out of the sky. Bullets ripping through metal and glass forced a crash landing in the woods; forced an impact with earth that shattered his leg and broke three vertebrae.

But Attridge wasn’t the victim of a surprise attack or Top-Gun style dog fight. He was simply at the wrong place a the wrong time. He shot himself down.

A Tiger F11F, the plane that Attridge was flying

In a run to test the plane’s weapons systems, Attridge fired a number of bullet bursts, increased his angle of descent, and fired some more. However, nearly a minute after firing his first burst he was pelted by gunfire—his own.

Now, we know this actually happened, so it pointless to speculate if a plane could really shoot itself down. But in the spirit of scientific investigation, I want to look at how such a “one-in-a-million” hit could happen, because science.

Trajectory and Trigonometry

Thanks to very detailed reports on the event, we know a lot about what happened that day. We know that Attridge fired his bullets at 13,000 feet and was struck at 7,000 feet. We know that his bullets were initially traveling at over 2,000 miles per hour and that the Tiger F11F he was piloting was screaming past the sound barrier at 880 miles per hour.

You may notice the speed of the bullets far exceeds the speed of the plane, meaning that there is no way the two paths could cross. But traveling over a few miles, bullets fired that fast can slow down significantly (if you have ever seen the MythBusters fire bullets into water you know what I mean). In fact, because we know that the bullets hit the plane, the bullets had to be going at least as fast as the plane at the time of impact (or slower).

We also know from reports that the plane traveled for about 11 seconds in a steeper dive than when the bullets were fired before it was hit. If the plane was going 880mph, this means that the Attridge covered a distance of 2.7 miles in that time. Then we basically have a right triangle, allowing us to dig up our old friend Pythagoras. Doing some trigonometry, this means Attridge covered a horizontal distance of 2.4 miles over the 6,000 foot dive.

All we have to do now is see if the bullets could have covered that distance in that time. Knowing all the numbers from the report, we can calculate the trajectory of the bullets. This basic calculator crunched the numbers for me and indicated that if the bullets slowed down enough, to maybe 50-60% of the plane’s speed (air resistance is a hell of a thing), then they could cover 2.4-3.0 miles in the time between them being fired and striking the plane—the same distance Attridge covered. In other words, yes, a plane could be shot down by its own bullets.

To check ourselves, what did the official report conclude? It says that the bullets slowed down enough the strike Attridge during a dive 2-3 miles after he fired them, just as we calculated! Science!

As for the “one-in-a-million” nature of this event, Attridge too recognizes the physics at play. If you are going that fast and take steep dives underneath where you shoot, this could happen again. He was quoted as saying:

At the speeds we’re flying today, [shooting yourself down] could be duplicated any time.