December 7, 2012: The U.S. has found a solution for the problem they have been having, for over two years, with rocket motor problems in their AIM-120 AMRAAM air-to-air missiles (and Sparrow missiles, which use a motor from the same manufacturer). The solution was to find another supplier who could produce rocket motors that worked. That turned out to be Norwegian ammunition manufacturer Nammo which has delivered 125 rocket motors so far and will soon be delivering a hundred motors a month. The former supplier, ATK, is still fixing the problem it had, which was the result of changing the formula for the rocket propellant several times to comply with environmental regulations. This led to their rocket motors becoming unreliable. It took over two years to sort all this out.

AMRAAM entered service two decades ago as a successor to Sparrow. Until recently, there have never been problems with the rocket motors. But as a result of the rocket problem, and the inability to fix it, no AMRAAM missiles have been delivered for two years. The AMRAAM solid fuel rocket motors problem was discovered during testing that the air force performs on a few of every new batch of missiles. The problem is that when rocket motors are exposed to very cold conditions (as would happen when an aircraft is flying at a high altitude) they become unreliable. The air force is withholding over half a billion dollars in payments until the reliability problem is fixed. ATK, the rocket motor manufacturer (for both the AMRAAM and Sparrow) insisted that it was building the rocket motors the same way it had for three decades. Recently it was discovered that the slight changes for environmental reasons had gradually changed the performance of the rocket motor. ATK makes rocket motors for all American air-to-air missiles, including Sidewinder.

AMRAAM has been around for a while and undergone several upgrades, without problems appearing in components that are often unchanged for decades. But there have been many upgrades, including a lot of new stuff. Thus, it was always suspected that some of the ingredients of the solid fuel (a slow burning explosive) rocket had changed and chemists scrambled to find out what change did what.

AMRAAM entered service in 1992, more than 30 years after the first radar guided air-to-air missile (the AIM-7 Sparrow) appeared. AMRAAM was designed to fix all the reliability and ease-of-use problems that cursed the AIM-7. But AMRAAM has only had a few opportunities to be used in combat but over half of those launched have hit something. The AIM-120D version entered service five years ago, has longer range, greater accuracy, and resistance to countermeasures. So far AMRAAMs have spent nearly 2 million hours hanging from the wings of jet fighters in flight. Some 2,400 AMRAAMs have been fired, mostly in training or testing operations. That’s about a quarter of those produced.

AMRAAM weighs 172 kg (335 pounds), is 3.7 meters (12 feet) long, and 178mm (7 inches) in diameter. AMRAAM has a max range of 70 kilometers. These missiles cost about a million dollars each. They are complex mechanical, electronic, and chemical systems and each of them, on average, suffers a component failure every 1,500 hours.

There were similar rocket motor problems with Sparrow missiles. The Taiwanese Air Force took all of its AIM-7 Sparrow air-to-air missiles (and a variant used for surface-to-air missions) out of service because of this. The missiles can now only be used if there is a war. This is because early last year the Sparrows began failing when tested. Taiwan bought over 1,100 Sparrows in the early 1990s, and most of them are still in service (although with a lot of upgraded or refurbished components). The manufacturer, Raytheon, warned all other users (over 15 nations) to limit use of their Sparrow missiles until the problem could be fixed. ATK also makes the rocket motors for Sparrow.

The most current version of Sparrow (AIM-7P) weighs 230 kg (510 pounds), is 200mm (7.9 inches) in diameter, and 3.7 meters (12 feet) long. Max range is 50 kilometers and it is still manufactured mainly as a surface-to-air missile. Sparrow costs less than half as much as an AMRAAM. Over 50,000 Sparrows, of all types, have been built and over 20 percent of those are still in service.

The air force and the navy have had an increasing number of incidents where their suppliers of high-tech weapons and equipment screwed up. Cancelling orders and taking manufacturers to court has not eliminated the problems. The military accuses the manufacturers of having a bad attitude, feeling that if there are problems it's easier to cozy up to members of Congress than it is to fix the technical problems. So far, that seems to be working, while the weapons and equipment don't.