An air-to-air missile (AAM) is a guided missile fired from an aircraft for the purpose of destroying another aircraft. It is typically powered by one or more rocket motors, usually solid fuelled but sometimes liquid fuelled. Ramjet engines, as used on the MBDA Meteor (currently in development), are emerging as propulsion that will enable future medium-range missiles to maintain higher average speed across their engagement envelope.
Air-to-air missiles are broadly grouped into short-range missiles - also called "dogfight" or "within visual range" (WVR) and medium- or long-range missiles - beyond visual range (BVR). Short-range missiles tend to use infrared guidance, while medium- and long-range missiles rely upon some type of radar guidance (and sometimes inertial guidance).
The air-to-air missile grew out of the unguided air-to-air rockets used since the First World War. German experience in World War II demonstrated that destroying a large aircraft was quite difficult, and they had invested considerable effort into guided missile systems like the never deployed Ruhrstahl X-4 to do this.
Post-war research led the Royal Air Force to introduce Fairey Fireflash into service in 1955 but their results were unsuccessful. The US Navy and US Air Force began equipping guided missiles in the 1956, deploying the USAF's AIM-4 Falcon and the USN's AIM-7 Sparrow and AIM-9 Sidewinder. The Soviet Air Force introduced its Kaliningrad K-5 into service in 1957. As missile systems have continued to advance, modern air warfare consists almost entirely of missile firing. The faith in Beyond Visual Range combat became so pervasive in the US that early F-4 variants were armed only with missiles in the 1960s. High casualty rates during the Vietnam War caused the US to reintroduce autocannons and traditional dogfighting tactics but the missile remains the primary weapon in air combat. In the Falklands War technically inferior British Harriers were able to defeat faster Argentinian opponents using AIM-9G missiles provided by the United States as the conflict began. The latest heat-seeking designs can lock onto a target from various angles, not just from behind, where the heat signature from the engines is strongest. Other types rely on radar guidance (either on-board or "painted" by the launching aircraft).
- See also: Missile guidance
Guided missiles operate by detecting their target (usually by either radar or infrared methods, although rarely others such as laser guidance or optical tracking), and then "homing" in on the target on a collision course.
The target is usually destroyed or damaged by means of an explosive warhead, often throwing out fragments to increase the lethal radius, typically detonated by a proximity fuze (or impact fuze if it scores a direct hit).
Note that although the missile may use radar or infra-red guidance to home on the target, this does not necessarily mean that the same means is used by the launching aircraft to detect and track the target before launch. Infra-red guided missiles can be "slaved" to an attack radar in order to find the target and radar-guided missiles can be launched at targets detected visually or via an infra-red search and track (IRST) system, although they may require the attack radar to illuminate the target during part or all of the missile interception itself.
Radar guidance is normally used for medium or long range missiles, where the infra-red signature of the target would be too faint for an infra-red detector to track. There are two major types of radar-guided missile - active and semi-active.
Active radar homing
Active radar (AR)-guided missiles carry their own radar system to detect and track their target. However, the size of the radar antenna is limited by the small diameter of missiles, limiting its range which typically means such missiles have to use two methods to get close to the target before turning their radar set on, often relying on guidance systems.
Semi-active radar homing
Semi-active radar (SAR)-guided missiles are simpler and more common. They function by detecting the radar energy reflected from the target, the radar energy is emitted from the launch aircraft's own radar signal. However, this means the launch aircraft has to maintain a "lock" on the target (keep illuminating the target aircraft with its own radar) until the missile makes the interception, limiting the attacking aircraft's ability to maneuver, which may be necessary should threats to the attacking aircraft appear. It also makes jamming the missile lock easier because the launching aircraft is further from the target than the missile, so the radar signal has to travel further and is greatly attenuated over the distance.
An early form of radar guidance was "beam-riding" (BR). In this method the attacking aircraft directed a narrow beam of radar energy at the target. The air-to-air missile was launched into the beam where sensors on the aft of the missile controlled the missile, keeping it within the beam. So long as the beam was kept on the target aircraft, the missile would ride the beam until making the interception. While simple in concept, the difficulty of simultaneously keeping the beam solidly on the target (which couldn't be relied upon to cooperate by flying straight and level), continuing to fly one's own aircraft, all the while keeping an eye out for enemy countermeasures, can be readily appreciated.
Infrared guided (IR) missiles home on the heat produced by an aircraft. Early infra-red detectors had poor sensitivity, so could only track the hot exhaust pipes of an aircraft. This meant an attacking aircraft had to maneuver to a position behind its target before it could fire an infra-red guided missile. This also limited the range of the missile as the infra-red signature soon become too small to detect with increasing distance and after launch the missile was playing "catch-up" with its target.
More modern infra-red guided missiles can detect the heat of an aircraft's skin, warmed by the friction of airflow, in addition to the fainter heat signature of the engine when the aircraft is seen from the side or head-on. This, combined with greater maneuverability, gives them an "all-aspect" capability, and an attacking aircraft no longer had to be behind its target to fire. Although launching from behind the target increases the probability of a hit, the launching aircraft usually has to be closer to the target in a tail-chase engagement.
An aircraft can defend against infra-red missiles by dropping flares that are hotter than the aircraft, so the missile homes in on the brighter, hotter target. Towed decoys and infra-red jammers can also be used. Some large aircraft and many combat helicopters make use of so called "hot brick" infra-red jammers, typically mounted near the engines. Current research is developing laser devices which can spoof or destroy the guidance systems of infra-redguided missiles.
However, the latest missiles such as the ASRAAM use an "imaging" infra-red seeker which "sees" the target (much like a digital video camera), and can distinguish between an aircraft and a point heat source such as a flare. They also feature a very wide detection angle, so the attacking aircraft does not have to be pointing straight at the target for the missile to lock on. The pilot can use a helmet mounted sight (HMS) and target another aircraft by looking at it, and then firing. This is called "off-boresight" launch. For example, the Russian Su-27 is equipped with an infra-red search and track (IRST) system with laser rangefinder for its HMS-aimed missiles.
In order to maneuver sufficiently from a poor launch angle at short ranges to hit its target, missiles are now employing gas-dynamic flight control methods such as vectored thrust, which allow the missile to start turning "off the rail", before its motor has accelerated it up to high enough speeds for its small aerodynamic surfaces to be useful.
A recent advancement in missile guidance is electro-optical imaging. The Israeli Python-5 has an electro-optical seeker that scans designated area for targets via optical imaging. Once a target is acquired, the missile will lock-on to it for the kill. Electro-optical seekers can be programmed to target vital area of an aircraft, such as the cockpit. Since it doesn't depend on the target aircraft's heat signature, it can be used against low-heat targets such as UAV's and cruise missiles.
Air-to-air missiles are typically long, thin cylinders in order to reduce their cross section and thus minimize drag at the high speeds at which they travel.
At the front is the seeker, either a radar system, radar homer, or infra-red detector. Behind that lies the avionics which control the missile. Typically after that, in the centre of the missile, is the warhead, usually several kilogrammes of high explosive surrounded by metal that fragments on detonation (or in some cases, pre-fragmented metal).
The rear part of the missile contains the propulsion system, usually a rocket of some type. Dual-thrust solid-fuel rockets are common, but some longer-range missiles use liquid-fuel motors that can "throttle" to extend their range and preserve fuel for energy-intensive final maneuvering. Some solid-fuelled missiles mimic this technique with a second rocket motor which burns during the terminal homing phase. There are missiles in development, such as the MBDA Meteor, that "breathe" air (using a ramjet, similar to a jet engine) in order to extend their range.
Modern missiles use "low-smoke" motors - early missiles produced thick smoke trails, which were easily seen by the crew of the target aircraft alerting them to the attack and helping them determine how to evade it.
Missiles are often cited with their maximum engagement range, which is very misleading. A missile's effective range is dependent on factors such as altitude, speed, position, and direction of target aircraft. For example the Vympel R-77 has stated range of 100 km. That's only true for a head-on, non-evading target at high altitude. At low altitude, the effective range is reduced by as much as 75%-80% to 20-25 km. If the target is taking evasive action, or in stern-chase position, the effective range is further reduced. See Air-to-Air missile non-comparison table for more information. The effective range of an air-to-air missile is known as the 'no-escape zone', noting the range at which the target can not evade the missile once launched.
Poorly-trained pilots, are known to fire their missiles at maximum-range engagement with poor results. In the 1998-2000 Eritrean-Ethiopian War, fighters from both sides shot over a dozen medium-range R-27 (AA-10 Alamo) missiles at distance with little effect. But when better-trained Ethiopian Su-27 pilots gave chase and attacked with short-range R-73 (AA-11 Archer) missiles, the results were often deadly to the Eritrean aircraft. 
A number of terms frequently crop up in discussions of air to air missile performance.
- Launch success zone
- The Launch Success Zone is the range within which there is a high (defined) kill probability against a target that remains unaware of its engagement until the final moment. When alerted visually or by a warning system the target attempts a last ditch manoeuvre sequence.
- A closely related term is the F-Pole. This is the slant range between the launch aircraft and target, at the time of interception. The greater the F-Pole, the greater the confidence that the launch aircraft will achieve air superiority with that missile.
- No-Escape Zone
- The No-Escape Zone is the zone within which there is a high (defined) kill probability against a target even if it has been alerted. This zone is defined as a conical shape with the tip at the missile launch. The cone's length and width are determined by the missile and seeker performance. A missile's speed, range and seeker sensitivity will mostly determine the length of this imaginary cone, while its agility (turn rate) and seeker complexity (speed of detection and ability to detect off axis targets) will determine the width of the cone.
Short-range air-to-air missiles used in "dogfighting" are usually classified into five "generations" according to the historical technological advances. Most of these advances were in infrared seeker technology (later combined with digital signal processing).
Early short-range missiles such as the early Sidewinders and Vympel K-13 (AA-2 Atoll) had infrared seekers with a narrow (30 degree) field of views and required the attacker to position them self behind the target (rear aspect engagement). This meant the target aircraft only had to perform a slight turn to move outside the missile seeker field of view and cause the missile to lose track of the target ("break lock").
Second generation missiles utilized more effective seekers that improved the field of view to 45 degrees.
This generation introduced "all aspect" missiles, because more sensitive seekers allowed the attacker to fire at a target which was side-on to itself, i.e. from all aspects not just the rear. This meant that while the field-of-view was still restricted to a fairly narrow cone, the attack at least did not have to be behind the target.
The Vympel R-73 (AA-11 Archer) entered service in 1985 and marked a new generation of dogfight missile. These missiles employed more advanced seeker technologies such as focal plane arrays that improved resistance to infrared countermeasures (IRCM) such as flares and increased off-bore sight capability to in excess of 60 degrees, i.e. a 120 degree field of view.
To take advantage of the increased field-of-view that now exceeded the capabilities of most aircraft radars also meant that helmet mounted sights gained popularity. Many newer missiles include what is known as "look-down-shoot-down" capability, as they could be fired onto low flying planes that would formerly be lost in ground clutter.
The latest generation of short-range missiles again defined by advances in seeker technologies, this time electro-optical imaging infrared (IIR) seekers that allow the missiles to "see" images rather than single "points" of infrared radiation (heat). The sensors combined with more powerful digital signal processing provide the following benefits:
- greater infrared counter countermeasures (IRCCM) ability, by being able to distinguish aircraft from infrared countermeasures (IRCM) such as flares.
- greater sensitivity means greater range and ability to identify smaller low flying targets such as UAVs.
- more detailed target image allows targeting of more vulnerable parts of instead of just homing in on the brightest infrared source (aircraft exhaust).
Examples of fifth generation missiles include:
- AIM-132 ASRAAM – Britain (1998–)
- AIM-9X Sidewinder – USA (2003–)
- IRIS-T – German lead consortium (2005–)
- Python 5 – Israeli
- A-Darter (under development) – South Africa
- Vympel R-74 – Russia (1994-)
List of missiles by country
For each missile, short notes are given, including an indication of its range and guidance mechanism.
- Mectron MAA-1 Piranha - short range IR
- Matra R550 Magic - short-range, IR guided
- Matra Magic II - IR guided missile.
- Magic Super 530F/Super 530D - medium-range, radar-guided
- MBDA MICA - medium-range, IR or radar guided
- Ruhrstahl X-4 - World War II design, first practical anti-aircraft missile, MCLOS, never saw service
- Henschel Hs 298 - World War II design, MCLOS, never saw service
- MBDA Meteor
- MBDA Meteor - medium range, active radar homing; design to replace AMRAAM
- IRIS-T - short range infrared homing; replacement for AIM-9 Sidewinder
- Astra missile BVRAAM (Undergoing developmental trials)
- Al Humurrabi- Long range, semi active radar
- Rafael Shafrir - first Israeli domestic AAM
- Rafael Shafrir 2 - improved Shafrir missile
- Rafael Python 3 - medium range IR-homing missile with all aspect capability 
- Rafael Python 4 - medium range IR-homing missile with HMS-guidance capability 
- Rafael Python 5 - improved Python 4 with electro-optical imaging seeker 
- Rafael Derby - Also known as the Alto, this is a medium-range, BVR active radar-homing missile 
- AAM-3 - short-range Type 90 air-to-air missile
- AAM-4 - middle-range Type 99 air-to-air missile
- AAM-5 - short-range Type 04 air-to-air missile
- Sarab 1 - Pakistani version of Matra Magic Missile, Short Range Missile Project Cancelled due to unsatisfactory results.
- H-2 BVR-AAM Infrared radar guided missile, developed by National Engineering and Scientific Commission (NESCOM)
- H-4 BVR-AAM Active radar-guided beyond visual range missile,developed by National Engineering and Scientific Commission (NESCOM)
- SD-10 - Jointly Developed by China and Pakistan
- PL-9 - Jointly Developed by Pakistan and China.
People's Republic of China
- PL-1 - PRC version of the Soviet Kaliningrad K-5 (AA-1 Alkali), retired.
- PL-2 - PRC version of the Soviet Vympel K-13 (AA-2 Atoll), which was based on AIM-9B Sidewinder.  Retired & replaced by PL-5 in PLAAF service.
- PL-3 - updated version of the PL-2, did not enter service.
- PL-5 - updated version of the PL-2, known versions include: 
- PL-5A - semi-active radar-homing AAM intended to replace the PL-2, did not enter service. Resembles AIM-9G in appearance.
- PL-5B - IR version, entered service in 1990s to replace the PL-2 SRAAM. Limited off-boresight
- PL-5C - Improved version comparable to AIM-9H or AIM-9L in performance
- PL-5E - All-aspect attack version, resembles AIM-9P in appearance.
- PL-7 - PRC version of the IR-homing French R550 Magic AAM, did not enter service. 
- PL-8 - PRC version of the Israeli Rafael Python 3 
- PL-9 - short range IR guided missile, marketed for export. One known improved version (PL-9C). 
- PL-10 - semi-active radar-homing medium-range missile based on the HQ-61 SAM,  often confused with PL-11. Did not enter service.
- PL-11 - medium-range air-to-air missile (MRAAM), based on the HQ-61C & Italian Aspide (AIM-7) technology. Limited service with J-8-B/D/H fighters. Known versions include: 
- PL-11 - MRAAM with semi-active radar homing, based on the HQ-61C SAM and Aspide seeker technology, exported as FD-60 
- PL-11A - Improved PL-11 with increased range, warhead, and more effective seeker. The new seeker only requires fire-control radar guidance during the terminal stage, providing a basic LOAL (lock-on after launch) capability.
- PL-11B - Also known as PL-11 AMR, improved PL-11 with AMR-1 active radar-homing seeker.
- LY-60 - PL-11 adopted for navy ships for air-defense, sold to Pakistan but does not appear to be in service with the Chinese Navy. 
- PL-12 (SD-10) - medium-range active radar missile 
- TY-90 - light IR-homing air-to-air missile designed for helicopters 
- Kaliningrad K-5 (NATO reporting name AA-1 'Alkali') - beam-riding
- Vympel K-13 (NATO reporting name AA-2 'Atoll') - short-range IR or SARH
- Kaliningrad K-8 (NATO reporting name AA-3 'Anab') - IR or SARH
- Raduga K-9 (NATO reporting name AA-4 'Awl') - IR or SARH
- Bisnovat R-4 (NATO reporting name AA-5 'Ash') - IR or SARH
- Bisnovat R-40 (NATO reporting name AA-6 'Acrid') - long-range IR or SARH
- Vympel R-23 (NATO reporting name AA-7 'Apex') - medium-range SARAH or IR
- Molniya R-60 (NATO reporting name AA-8 'Aphid') - short-range IR
- Vympel R-33 (NATO reporting name AA-9 'Amos') - long range active radar
- Vympel R-27 (NATO reporting name AA-10 'Alamo') - medium-range SARH or IR
- Vympel R-73 (NATO reporting name AA-11 'Archer') - short-range IR
- Vympel R-77 (NATO reporting name AA-12 'Adder') - medium-range active radar
- Vympel R-37 (NATO reporting name AA-X-13 'Arrow') - long-range SARH or active radar
- Novator KS-172 AAM-L - extreme long range, inertial navigation with active radar for terminal homing
- Sky Sword I (TC-1) - air-to-air
- Sky Sword II (TC-2) - air-to-air
- Fireflash - short range beam-riding
- Firestreak - short range IR
- Red Top - short range IR
- Skyflash - medium-range radar-guided missile based on the AIM-7E2, said to have quick warm-up times of 1 to 2 seconds.
- AIM-132 ASRAAM - short range IR
- MBDA Meteor - long range radar guided missile due to enter service in 2013.
- AIM-4 Falcon - radar (later IR) guided
- AIM-7 Sparrow - medium range semi-active radar
- AIM-9 Sidewinder - short range IR
- AIM-54 Phoenix - long range, semi-active and active radar
- AIM-120 AMRAAM - medium range, active radar; replaces AIM-7 Sparrow