By Steve Colby | July 1, 2007
THIS MONTH IT’S TIME TO TALK about combat threats to helicopters and what we can do about them. Survivability was broadly defined in the last article, so today I’ll focus on how to survive against man-portable, air-defense systems (manpads).
Combat unit training scenarios must include a continuum of threat levels designed to train students to avoid, degrade, defeat, or destroy threat systems to survive. Manpads present one of the most lethal threats to helicopters since Vietnam. Training to deal with them is essential.
There are key advantages in the manpad’s court. First, they are widely and numerously distributed throughout the world. Second, they are a passive-detection threat, usually designed to home in on the target aircraft’s heat signature. Missile designers employ various seeker-design techniques for quick lock-on and guidance to impact. Understanding seeker weaknesses is the key to unlocking the magic of infrared (IR) missiles and degrading or defeating them. They are unbelievably fast, difficult to see in flight, and lethal, but beating them is not impossible.
Older manpads relied on lead sulfide (PbS) detector elements that were most sensitive to the IR spectrum associated with hot metal parts (1-2 mm, Band I) in the aft engine area. This generation used spin-scan reticles that constantly modulated (chopped) the detected target’s IR energy to allow the guidance system to steer the missile to the nulled-center of the missile’s field of view. Second-generation systems incorporate different compounds, like indium antimonide (InSb) or mercad telluride (HgCdTe), in the detector. These are sensitive to the Band IV (3-5 mm) IR spectrum, which corresponds to engine exhaust plumes. These newer seekers are generally cooled by nitrogen-gas cryogenics to eliminate unwanted IR "noise," making them more sensitive to cooler targets. The reticle design was upgraded to a conical-scan-style whose wobbling seeker pattern resembles a Spirograph roulette trace. These cooled seekers allowed operators to engage target aircraft from the front. The third-generation models use seekers with two different IR "color"-sensitive detectors to assist the missile in rejecting hotter countermeasures like flares and older IR jammers. The latest generation seekers employ imaging techniques that rely much less on IR energy than the target’s shape and contrasts.
To beat these systems, one must plan backward from the objective to the starting point. Plan a route that avoids the threat as best known or briefed by intelligence to increase your survivability. If routing simply cannot allow the avoidance of a threat weapons-engagement zone, plan to fly at an altitude that degrades the missile’s capabilities. Flying low in rugged terrain, of course, masks the aircraft from direct line of sight but also introduces terrain that may present a heat-clutter environment that makes locking on the aircraft difficult for missile operators.
Some tactical helicopters choose to fly at high altitudes (radar surface-to-air threat permitting) at or just above the manpad’s maximum engagement height. The IR signature distortion induced by atmospheric scattering and absorption makes it difficult for some missile systems to obtain a heat signature lock.
If you must fly through the engagement zone at lower altitudes, you better have some sort of aircraft survivability equipment (ASE) installed, like a missile warning system, and flares or a jammer or both. Planning to fly evasive maneuvers against IR manpads without ASE is foolhardy. IR missile "latency" or guidance system response time is extremely short. Attempting to generate a miss distance with only an aggressive maneuver will most likely result only in moving the missile impact point on your aircraft. Therefore, defeating the missile by decoying or deceiving the guidance system becomes essential to survival.
In-depth knowledge of your ASE system is paramount to ensure proper operational settings for the most probable threat in your theater. Newer systems that combine missile warning systems with turrets that direct modulated energy toward inbound missiles show remarkable capability. But it’s best to have flares as a back-up. Newer design flares emit strong signal intensity in Band IV, making a tough-to-discern target for those two-color seeker missiles.
Your training scenarios must incorporate the entire spectrum of "avoid, degrade, defeat, destroy" to train like you fight. Be critical of improper maneuver or expendable responses. Retry your erroneous engagements whenever you can to demonstrate and enforce the proper response. Lastly, make your students actually touch the switches required for flare dispense (with appropriate safety measures in place) or jammer operation to exercise their muscle memory for those critical actions. Manual flare responses to visual missile engagements must be as automatic as lowering collective for an autorotation or it will simply be too late. It’s been said that "unused flares on a burning wreck are wasted."
Combat units must incorporate survivability training elements to minimize threat kill probability while flying in harm’s way. We owe it to our combat helicopter warriors.