Countermeasures for airliners: not as simple as it seems
By Edward Downs, Editor, Jane's Avionics
In the aftermath of 9/11, the missile attack on a Israeli Arkiav flight in Mombassa during November 2002 and a number of terrorist alerts around the world's airports, manufacturers of missile countermeasures systems are ramping up their efforts in anticipation of large orders for the world's airline fleets. Systems fall into two broad categories: dispenser-based systems (flares) and directed energy systems (lamps or lasers). The former category includes the Elta/IMI Flight Guard and the latter the Northrop Grumman/BAE Systems Directional Infra Red Counter Measures (DIRCM) system.
While military aircraft almost exclusively employ countermeasures dispenser systems (CMDS), deploying chaff and/or flares to counter attacking missiles, this traditional solution is fraught with problems in the transition to the civilian environment. Expendables, by their very definition, are ejected from the aircraft, which raises a few points. Larger aircraft with widely spread engines, for example, can appear as multiple targets, requiring any flare 'shroud' to cover a large volume behind the aircraft that would potentially require a large number of flares to be deployed against any attack. Also, depending on the height of the aircraft at flare ejection, there would be a risk of burning flares hitting the ground around the airport; noting the position of many of the world's airports, this could pose a significant risk to the civilian population. This problem would not necessarily be solved by short-burn flares; with a screen height of 35/15ft during the critical take-off phase, airliners are at their most vulnerable when extremely close to the ground. Further, flares are most effective when the aircraft also manoeuvres to move out of the incoming missile's field of view (FoV), which is not feasible with respect to a heavily laden airliner. However, flares have a proven track record against the type of shoulder-launched missile currently favoured by the world's terrorists and such systems are cheaper to buy than the latest directed-energy systems and would present a lesser drag (and therefore range) penalty to a civil airliner.
The latest laser-based DIRCM systems, which seem to be the favoured solution for the majority of manufacturers, including Rafael (Britening) and Elbit (MUSIC), employ no expendables, so are a 'cleaner' solution for the civil world but are not without their own limitations. They are more expensive and would require multiple turrets to protect the largest Boeing and Airbus ultra long-range types. There are also some questions regarding the effectiveness of these systems against multiple incoming missiles. Furthermore, the increase in drag on a large airliner resulting from two or more DIRCM turrets protruding into the air stream would be costly to operators in terms of fuel burn and thus maximum range. When modern airliners are designed and acquired with particular ATS routes in mind, this effect should not be disregarded.
As a final point in considering the fitment of countermeasures systems on airliners, integration and operation issues should be carefully considered. While no-one would dispute the requirement for a fully automatic system with no requirement for reaction (and thus delay) by the crew, should another aircraft fall under the control of terrorists, the job of fighter combat air patrols around major cities might be undermined by the rogue aircraft's inherent defensive capability.
The Elta/IMI FlightGuard is based on Elta's Missile Warning System (MWS) and IMI's Counter Measures Dispenser System (CMDS)