The AIM-120 Advanced Medium-Range Air-to-Air Missile, or AMRAAM (pronounced AM-ram), is an American beyond-visual-range air-to-air missile (BVRAAM) capable of all-weather day-and-night operations. Designed with a 7-inch (180mm) diameter form-and-fit factor, and employing active transmit-receive radar guidance instead of semi-active receive-only radar guidance, it has the advantage of being a fire-and-forget weapon when compared to the previous generation Sparrow missiles. When an AMRAAM missile is launched, NATO pilots use the brevity code Fox Three.
The AMRAAM is the world’s most popular beyond-visual-range missile; more than 14,000 have been produced for the United States Air Force, the United States Navy, and 33 international customers. The AMRAAM has been used in several engagements and is credited with ten air-to-air kills. Now over 30 years old in design, the AMRAAM is due to be replaced by the new AIM-260 JATM, which will offer better long-range performance and ability to defeat electronic warfare jamming.
AMRAAM was developed as the result of an agreement (the Family of Weapons MOA, no longer in effect by 1990), among the United States and several other NATO nations to develop air-to-air missiles and to share production technology. Under this agreement the U.S. was to develop the next generation medium range missile (AMRAAM) and Europe would develop the next generation short range missile (ASRAAM). Although Europe initially adopted the AMRAAM, an effort to develop the Meteor, a competitor to AMRAAM, was begun in Great Britain. Eventually the ASRAAM was developed solely by the British, but using another source for its infrared seeker. After protracted development, the deployment of AMRAAM (AIM-120A) began in September 1991 in US Air Force F-15 Eagle fighter squadrons. The US Navy soon followed (in 1993) in its F/A-18 Hornet squadrons.
The Russian Air Force counterpart of AMRAAM is the somewhat similar R-77 (NATO codename AA-12 Adder), sometimes referred to in the West as the “AMRAAMski” Likewise, France began its own air-to-air missile development with the MICA concept that used a common airframe for separate radar-guided and infrared-guided versions.
Operational features summary
AMRAAM has an all-weather, beyond-visual-range (BVR) capability. It improves the aerial combat capabilities of US and allied aircraft to meet the threat of enemy air-to-air weapons as they existed in 1991. AMRAAM serves as a follow-on to the AIM-7 Sparrow missile series. The new missile is faster, smaller, and lighter, and has improved capabilities against low-altitude targets. It also incorporates a datalink to guide the missile to a point where its active radar turns on and makes terminal intercept of the target. An inertial reference unit and micro-computer system makes the missile less dependent upon the fire-control system of the aircraft.
Once the missile closes in on the target, its active radar guides it to intercept. This feature, known as “fire-and-forget”, frees the aircrew from the need to further provide guidance, enabling the aircrew to aim and fire several missiles simultaneously at multiple targets and break a radar lock after the missile seeker goes active and guide themselves to the targets.
The missile also features the ability to “Home on Jamming,” giving it the ability to switch over from active radar homing to passive homing – homing on jamming signals from the target aircraft. Software on board the missile allows it to detect if it is being jammed, and guide on its target using the proper guidance system.
Guidance system overview
Interception course stage
AMRAAM uses two-stage guidance when fired at long range. The aircraft passes data to the missile just before launch, giving it information about the location of the target aircraft from the launch point and its direction and speed. The missile uses this information to fly on an interception course to the target using its built-in inertial navigation system (INS). This information is generally obtained using the launching aircraft’s radar, although it could come from an infra-red search and track system, from a data link from another fighter aircraft, or from an AWACS aircraft.
After launch, if the firing aircraft or surrogate continues to track the target, periodic updates—such as changes in the target’s direction and speed—are sent from the launch aircraft to the missile, allowing the missile to adjust its course, via actuation of the rear fins, so that it is able to close to a self-homing distance where it will be close enough to “catch” the target aircraft in the basket (the missile’s radar field of view in which it will be able to lock onto the target aircraft, unassisted by the launch aircraft).
Not all armed services using the AMRAAM have elected to purchase the mid-course update option, which limits AMRAAM’s effectiveness in some scenarios. The RAF initially opted not to use mid-course update for its Tornado F3 force, only to discover that without it, testing proved the AMRAAM was less effective in beyond visual range (BVR) engagements than the older semi-active radar homing BAE Skyflash weapon—the AIM-120’s own radar is necessarily of limited range and power compared to that of the launch aircraft.
Terminal stage and impact
Once the missile closes to self-homing distance, it turns on its active radar seeker and searches for the target aircraft. If the target is in or near the expected location, the missile will find it and guide itself to the target from this point. If the missile is fired at short range, within visual range (WVR) or the near BVR, it can use its active seeker just after launch to guide it to intercept.
Boresight Visual mode
Apart from the radar-slaved mode, there is a free guidance mode, called “Visual”. This mode is radar guidance-free—the missile just fires and locks onto the first thing it sees. This mode can be used for defensive shots, i.e. when the enemy has numerical superiority
|Mass||335 lb (152 kg)|
|Length||12 ft (3.7 m)|
|Diameter||7 in (180 mm)|
|Warhead||High explosive blast-fragmentation
• AIM-120A/B: WDU-33/B, 50 pounds (22.7 kg)
• AIM-120C-5: WDU-41/B, 40 pounds (18.1 kg)
|Active RADAR Target Detection Device (TDD)
Quadrant Target Detection Device (QTDD) in AIM-120C-6 – lots 13+.
|Engine||Solid-fuel rocket motor|
|Wingspan||20.7 in (530 mm) AIM-120A/B|
|• AIM-120A/B: 55–75 km (30–40 nmi)
• AIM-120C-5: >105 km (>57 nmi)
• AIM-120D (C-8): >160 km (>86 nmi)
|Maximum speed||Mach 4 (4,900 km/h; 3,045 mph)|
|inertial guidance, terminal active radar homing|