The Jet Plane that Shot Itself Down

An F11F-1 Tiger, tail number 138620, is a plane that became famous as being the first documented incident of a jet plane that shot itself down!

On September 21st, 1956, Thomas W. Attridge Jr, a Grumman test pilot, was conducting test-firing of the aircraft’s four 20mm cannon (Colt Mark-12) at around Mach 1.0, aiming for a patch of open ocean off the coast of Long Island, NY.

Starting his run at 20,000ft, Attridge entered a shallow dive at 20° nose-down. When he reached 13,000ft, he pulled the trigger for a four second cannon burst, advanced the throttle to afterburner, steepened his descent, and fired a second burst to empty the magazine belts. Whilst firing, his plane continued in the descent, passing through to 7,000ft

About a minute (and 2.7 miles) after the first volley, he was hit by the first bullets he’d fired himself!

Even though the bullets were initially travelling well over 2,000 mph (the speed of the plane plus the muzzle velocity of the cannon), they slowed down quickly due to drag. Also, Attridge’s plane continued to accelerate in afterburner fueled descent, and the cruel consequence of these coincidences was that both entities ended up occupying the same space at the same time. Unlucky!

Attridge became aware of the incident when the plane rattled, and his windshield buckled inwards, He’d been hit.

Attridge throttled back to slow down and prevent cave-in of the windshield (His thoughts were that maybe he’d had a bird strike), and attempt to fly back to Grumman’s Long Island field at 200 knots. He radioed that a gash in the outboard side of the right engine’s intake lip was the only apparent sign of damage, other than for the glass but, more worryingly, only 78 percent engine power was available without severe roughness.

Two miles out, at 1,200 ft with flaps and wheels down, it became evident from the sink rate that the runway could not be attained at this low power setting. Attridge applied power, and is quoted as saying the engine made a noise like “a Hoover vaccum cleaner picking up gravel from a rug.”

Shortly after, the engine lost power completely. He pulled up the gear and dead-sticked a landing, settling into trees, half a mile short of the runway. He gouged a path 300 feet long in the decelerating impact (losing a right wing and stabilizer in the process); fire broke out from the unburnt fuel. Despite injuries, Attridge managed to cut himself free of the plane and get far enough away from the crash. The Sikorsky S-58 helicopter dispatched to retrieve him also damaged its blades from contact with foliage during the rescue.

A post-accident investigation revealed that Attridge’s aircraft had been hit by three of the 20mm bullets he’d fired. The first penetrated his windshield, the second punctured the nose, and the third damaged the right engine intake, struck the inlet guide vanes, and lodged in the first stage compressor of the engine. This bullet was recovered and a picture of it is shown on the left.

Attridge survived the crash with a shattered leg, and three broken vertebrae. He successfully returned to flight status less than six months later, and continued on to a long and distinguished career in the aerospace industry, becoming the project manager of the LEM-3, the first lunar module rated for human flight (flown on Apollo 9), and later as VP of Grumman Ecosystems, the company’s environmental management and research venture.

Blue Angels

Interestingly, the F11F saw limited service as it was eclipsed by two more modern aircraft: F8U Crusader and F4H Phantom II. Tigers finished their service in the Naval Air Training Command and as demonstration aircraft with the Blue Angels, who flew the F11F during the period 1957-1969.

Datagenetics.com

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