AIM-9 Explodes on the Test Stand

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AIM-9 Sidewinder missile fired from an F/A-18C

My job in the Air Force was Aging and Surveillance Testing of missiles--everything from the AIM-9 Sidewinder air-to-air missile all the way up to the Minuteman ICBM.

In my Air Force service between 1972 and 75, I never got closer to Viet Nam than the western desert of Utah, but test firing missiles can be dangerous.  My first brush with missile-induced death only caused minor, temporary hair loss.  The second was a lot worse, but more on that later.

On a warm, spring Friday in 1973, we were scheduled to fire 20 AIM-9 Sidewinder missiles in a test stand.  The missile test area was in the northwest corner of Hill Air Force Base, three miles from main base and the airfield. It was also out of the flight path of the two runways, since we could occasionally send up clouds of smoke from test firings that changed from burn to explosion.  Today was one of those days. 

Weeks before the test, we received a shipment of AIM-9s randomly selected by lot number.  We then froze the missiles in a large freezer. We shook them on a vibration table that was a huge 300,000-Watt speaker driver.  We simulated various stratospheric heights in the altitude chamber, then finally took the stressed missiles, bolted them to a test stand, attached accelerometers, and fired them.

On a good day we could fire one every ten minutes, allowing for burn time and time for the spent missile and for spinning the big screws that locked the missile into the test stand. By the time of this test, I had been on the fire crew of several batches of AIM-9s. 

The crew leader was Staff Sergeant John Pachuca.  He would retire the following year with 20 years of service. Hill was his only duty station in more than a decade. In the 60s, missile testing consolidated at Hill. Several other sergeants planned on retiring at Hill.  But this stable environment also meant that promotions were few and far between, so Big John Pachuca would retire a staff sergeant. Before he retired, my muscular Mexican-American crew chief would save my life.  

After each missile was fired, we counted to ten in a ditch several yards away from the concrete test stand. I waited in the trench till the noise stopped, and then vaulted the wall to switch the missile. Two of us ran to the stand and unscrewed the clamps while two more grabbed the next missile.  We used asbestos gloves to carry away the casing of the spent missile. 

The stand was covered with a shelter made from perforated steel planking or PSP. They were more the sheets were ten feet long, fifteen inches wide and weighed more 66 pounds. They were designed to be temporary runways during World War II, but were also great as temporary roadways or to make a cover that allowed smoke to blow through. PSP sheets are full of holes.

Since it was Friday, we all wanted to get done, so we sprinted to get the fired missile out of the stand and the next missile locked in.  When a missile fires, it roars for several seconds then the sound dies away. Each missile has a unique burn time and part of the test was recording that burn time.  Burn time was not my part of the test. The test went well in the morning, but after lunch a few glitches with electronic equipment slowed us down. We wanted to get done and have a weekend off, so we moved as fast as we could bolting the missiles to the stand, then removing the fired missile.  After three firings in the afternoon we had a rhythm again.  The fourth missile fired and burned, but the burn time was about two seconds too short.  I started to vault the wall then suddenly flipped backwards. I thought the top of my head was being torn off. 

I started yelling with pain and swinging wildly. I shut up when I saw the flash of the entire test pad blowing apart.  I looked up and saw a sheet of PSP fly over the ditch we were in. If I had been standing above the ditch, the ten-foot steel sheet would have cut me in half.  John Pachuca had grabbed my by the hair—which was three inches long and barely in Air Force regulations—and thrown me back in the ditch. He knew the burn was too short and heard the sputter before the missile exploded. 

Inside the missile, the propellant cracked during the freezing and shaking. The air gap caused the propellant to stop burning, but then heat in the casing caused the remaining propellant to heat and sizzle.

Then the AIM9 blew up on the pad.

I was lying on back in the ditch with the big sergeant in the white overalls on top of me.  My head hurt for days. Until sundown and much of the next day we cleaned up what we could of the mess. Engineering teams had to rebuild the test stand.  We continued the test the following week.  The test site had another pad because when missiles go high order they blow up everything around them.

The next time a missile test went wrong I wasn’t so lucky.