In 1975 the United States Air Force (USAF) and United States Navy (USN) launched a joint project to produce a follow-on missile to the AIM-7 Sparrow. In December 1981 following a fly-off competition between Hughes and Raytheon, Hughes's AMRAAM was selected as the AIM-7 replacement. The Sparrow (in use since the 1960's) although a good missile has one major flaw, no fire and forget capability. The AIM-7 is termed a semi-active missile requiring the launch aircraft to continuously illuminate its target, the Sparrow homes onto the reflected radar energy. This has two major pitfalls, firstly by continuously emitting radio waves the target aircraft has an opportunity to accurately plot the launch aircraft's position (assuming the enemy has the required systems to achieve this). Secondly the requirements to maintain continuous illumination prevent the launch aircraft from manoeuvring out of range of any potential return shot from the enemy aircraft. These two problems combined obviously open the launch aircraft up to a potentially serious threat.

Raytheon/Hughes AMRAAM

The AIM-120 Avanced Medium Range Air to Air Missile, or AMRAAM (like Sparrow) is a Beyond Visual Range (BVR) weapon designed to engage an enemy well before the pilot can see it. Overall improvements compared to Sparrow include; greater range, higher speed and improved manoeuvrability. The most obvious improvement though is that AMRAAM is now a fully active missile. To achieve this the missile is fitted with three separate targeting and navigation systems; a datalink to the launch aircraft, an on-board Inertial Navigation System (INS) and finally an active radar assembly. The missile itself comprises basically four sections; propulsion (solid rocket based yielding a top speed of around Mach 4), control/electronics, an 18kg (40lb) HE fragmentation warhead and guidance all wrapped up in a lightweight aluminium structure. The interface to the launch aircraft uses the now standard -1553B weapons databus. Integration requirements to use AMRAAM are thus an appropriate weapons interface (either built-in or provided by some intermediate launch rail such as the LAU-127 used on F-18 Hornet's) and appropriate radar mode support.

At the present time there are essentially three variants of the missile; AIM-120A, AIM-120B and AIM-120C. The second of these, AIM-120B improves upon the -120A by allowing in the field reprogramming of the missile control software (the AIM-120A's is hardwired) using a system known as Common Field-level Memory Reprogramming Equipment or CFMBE. The AIM-120C is essentially a clipped fin version of the -120B to allow a greater number of weapons to carried within the F-22 Raptor's internal ventral bay (six AIM-120C's may be carried compared to four -120A/Bs).

A typical AMRAAM engagement may see the launch aircraft acquiring a target at between 20 and 30nm. AMRAAM can then be launched using initial data from the aircraft's systems. During flight the missile can rely on its own INS to guide it to the target area with updates provided by the launch aircraft if available. During the final (or terminal) phase AMRAAM switches on its own mono-pulse radar and searches for the target aircraft. The system also features a home-on-jam mode to counter attempts by the enemy aircraft to spoof the missile. The missile is equipped with a laser proximity fuzz causing detonation of the fragmentation warhead at a pre-set distance from the aircraft.

Although AMRAAM has already proven itself in combat as well as numerous trials there are a number of identified problems. These include; weak seeker (compared to the current state of the art), low terminal phase velocity and a relatively smoky propellant. To this end the United Kingdom launched a requirement for a new medium range weapon system (primarily intended as the RAF's Eurofighter BVR weapon), termed BVRAAM. Similarly Raytheon are investigating a number of improvements to AMRAAM independently of its proposed solution to the UK requirement (termed FMRAAM) including; ram-rocket motor, dual band seeker and improved aerodynamics. At this time it is not clear whether the United States intend to support these improvements (the outcome is likely dependent upon which solution the UK chooses for BVRAAM which is due in mid-1999/early-2000).

* : Note that all ranges quoted are based on mean figures from various data sources. Actual achievable range will depend on a great number of factors and may be no where near those quoted.