Flare (countermeasure)

In contrast to radar-guided missiles, IR-guided missiles are very difficult to find as they approach aircraft. They do not emit detectable radar, and they are generally fired from behind, directly toward the engines. In most cases, pilots have to rely on their wingmen to spot the missile's smoke trail and alert of a launch. Since IR-guided missiles have a shorter range than their radar-guided counterparts, good situational awareness of altitude and potential threats continues to be an effective defense. More advanced electro-optical systems can detect missile launches automatically from the distinct thermal emissions of a missile's rocket motor.

Once the presence of a "live" IR missile is indicated, flares are released by the aircraft in an attempt to decoy the missile. Some systems are automatic, while others require manual jettisoning of the flares. The aircraft would then pull away at a sharp angle from the flare (and the terminal trajectory of the missile) and reduce engine power in attempt to cool the thermal signature. Ideally the missile's seeker head is then confused by this change in temperature and flurry of new heat signatures, and starts to follow one of the flares rather than the aircraft.

More modern IR-guided missiles have sophisticated on-board electronics and secondary electro-optical sensors that help discriminate between flares and targets, reducing the effectiveness of flares as a reactionary countermeasure. A newer procedure involves preemptively deploying flares in anticipation of a missile launch, which distorts the expected image of the target should one be let loose. This "pre-flaring" increases the chances that the missile then follows the flares or the open sky in between, rather than a part of the actual defender.

As non-state combatants such as insurgents and terrorists gain access to anti-air missiles, there is an increasing trend to equip slower-moving helicopters with flare countermeasures. Consequently, flare dispensers have become a regular feature on military helicopters. Almost all of the UK's helicopters, whether they are transport or attack models, are equipped with flare dispensers or missile approach warning systems. Similarly, the US armed forces have adopted active defenses with their helicopters.

Apart from military use, some civilian aircraft are also equipped with countermeasure flares, against terrorism: the Israeli airline El Al, having been the target of the failed 2002 airliner attack, in which shoulder-launched surface-to-air missiles were fired at an airliner while taking off, began equipping its fleet with radar-based, automated flare release countermeasures from June 2004.[1][2] This caused concerns in some European countries, which proceeded to ban such aircraft from landing at their airports.[3]

A C-130 Hercules deploying flares

C-130 flare and chaff dispensers

Flares burn at thousands of degrees Celsius, which is much hotter than the exhaust of a jet engine. IR missiles seek out the hotter flame, believing it to be an aircraft in afterburner or the beginning of the engine's exhaust source.

As the more modern infrared seekers tend to have spectral sensitivity tailored to more closely match the emissions of airplanes and reject other sources (the so-called CCM, or counter-countermeasures), the modernized decoy flares have their emission spectrum optimized to also match the radiation of the airplane (mainly its engines and engine exhaust). In addition to spectral discrimination, the CCMs can include trajectory discrimination and detection of size of the radiation source.

The newest generation of the FIM-92 Stinger uses a dual IR and UV seeker head, which allows for a redundant tracking solution, effectively negating the effectiveness of modern decoy flares (according to the U.S. Department of Defense). While research and development in flare technology has produced an IR signature on the same wavelength as hot engine exhaust, modern flares still produce a notably (and immutably) different UV signature than an aircraft engine burning kerosene jet-fuel.

HMS Dragon's Westland Lynx helicopter fires flares during an exercise over the Type 45 destroyer

A Dutch Eurocopter AS532 Cougar fires its flares during a night exercise.

Polish Air Force MiG-29 at the 2014 Rome International Air Show

An F-15E Strike Eagle releasing flares

For the infrared generating charge, two approaches are possible: pyrotechnic and pyrophoric as stored, chemical-energy-source IR-decoy flares contain pyrotechnic compositions, liquid or solid pyrophoric substances, or liquid or solid highly flammable substances.[4]

Upon ignition of the decoy flare, a strongly exothermal reaction is started, releasing infrared energy and visible smoke and flame, emission being dependent on the chemical nature of the payload used.

There is a wide variety of calibres and shapes available for aerial decoy flares. Due to volume storage restrictions on board platforms, many aircraft of American origin use square decoy flare cartridges. Nevertheless, cylindrical cartridges are also available on board American aircraft, such as MJU 23/B on the B-1 Lancer or MJU-8A/B on the F/A-18 Hornet; however, these are used mainly on board French aircraft and those of Russian origin (e.g. PPI-26 IW on the MiG 29).

Schematic view of a MJU-7A/B decoy flare cartridge : anodised aluminium cartridge (1); an electrical impulse cartridge (2), providing both expulsion and, in some cases, direct ignition of the payload; a pusher plate acting as a safe&arm device (3); the payload (4) with first fire layer (5); the wrapping self-adhesive polyester reinforced aluminum foil (6); and a front washer (7).

Square calibres and typical decoy flares:

• 1x1x8 Inch e.g. M-206, MJU-61, (Magnesium/Teflon/Viton (MTV) based) M-211, M-212 (spectral flares)
• 2x1x8 Inch e.g. MJU-7A/B (MTV based), MJU-59/B (spectral flare)
• 2x2.5x8 Inch e.g. MJU-10/B (MTV based)

Cylindrical calibres and typical decoy flares:

• 2.5 Inch e.g. MJU-23/B (MTV based)
• 1.5 Inch e.e. MJU 8 A/B (MTV based)
• 1 Inch e.g. PPI 26 IW

Spectrally balanced payloads

A sectional of the typical LLU-2B ground illumination flare

Other payloads provide large amounts of hot carbon dioxide upon combustion and thus provide a temperature-independent selective emission in the wavelength range between 3 and 5 μm. Typical pyrotechnic payloads of this type resemble whistling compositions and are often made up from potassium perchlorate and hydrogen lean organic fuels.[7] Other spectrally balanced payloads are made up similarly as double base propellants and contain nitrocellulose (NC), and other esters of nitric acid [8] or nitro compounds as oxidizers such as hexanitroethane and nitro compounds and nitramines as high-energy fuels.[9]

• Anti-aircraft
• Anti-ballistic missile
• Countermeasure
• Electronic countermeasure

• Media related to Decoy flares at Wikimedia Commons