Air Weapons: Sparrows Catch The AMRAAM Disease


August 1, 2012: The Taiwanese Air Force has taken all of its AIM-7 Sparrow air-to-air missiles (and a variant used for surface-to-air missions) out of service. The missiles can now only be used if there is a war. This is because early last year the Sparrows began failing when tested. Over a year of investigations failed to find a cause, much less a cure. The main problem is the rocket motor, although some other components appear to be involved as well. 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 can be fixed.

Meanwhile Raytheon is facing a similar problem (defective rocket motors) with it AIM-120 AMRAAM air-to-air missiles. AMRAAM entered service two decades ago as a successor to Sparrow. But as a result of the rocket problem, and the inability to fix it, no AMRAAM missiles have been delivered for nearly 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. At the same time the manufacturer is frantically trying to discover the cause of the failures. ATK, the rocket motor manufacturer (for both the AMRAAM and Sparrow) insists that it is building the rocket motors the same way it has for three decades. So far ATK has not said much about the progress of its investigation, other than no solution has yet been found.

AMRAAM has been around for a while and undergone several upgrades, without problems appearing in components that are often unchanged for 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 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 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, 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.

The most current version of Sparrow (AIM-7P) weighs 230 kg (510 pounds) and 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.


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