AMRAAM has been around for a while and undergone several upgrades, without problems appearing in components that are often built the same way they have been for decades. But there have been many changes to components, including lots of new stuff. Thus it's likely that some of the components of the solid fuel (a slow burning explosive) rocket have changed and chemists are scrambling to find out what it is.
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 had only had a few opportunities to be used in combat, and over half of those launched have hit something. The AIM-120D version entered service five years ago and has longer range and 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.
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.