Military

IFF INTERROGATION

When the target is visually detected, point the launcher toward the target, sight over the sight assembly, and then look through the peep sight. Next, position the target image in the center of the range ring. Challenge the aircraft if it has not already been identified. (Chapter 4 discusses when to challenge and under what conditions.)

Listen for the IFF response. IFF responses have the following meanings:

Depending upon the IFF response and the rules of engagement, either disengage or proceed to engage the target.

TRACKING AND RANGING THE TARGET

Track the target by keeping it in the range ring. The stance and upper body are determined by the aircraft's direction of flight. The stance requires that the left foot be placed directly toward the aircraft and the body be leaned slightly forward. Then the technique of fire applicable to the type of aircraft being engaged is applied. Target tracking occurs prior to weapon activation and continues throughout the engagement sequence. Target tracking is further discussed in chapter 6.

WEAPON ACTIVATION

Activate the weapon as soon as required by the firing doctrine. Firing doctrine is discussed in chapter 6. Weapon activation occurs when the safety and actuator device is operated. Press the device forward, outward, and down with the right thumb until a click is heard. This activates the BCU. Then, release the safety and actuator device. Weapon "warmup" occurs within a period of 3 to 5 seconds, during which time certain components are brought up to the mechanical and electrical conditions required for system operation. Gyro spin-up noise, which indicates the system is becoming operational, should be heard.

IR ACQUISITION/DISCRIMINATION

The Stinger missile seeker is sensitive to radiations in the infrared frequency spectrum and uses these radiations from the target as the source to guide itself to target intercept. After a target has been visually acquired and tentatively identified, the gunner must track the target to enable the missile to lock on the target IR. The IR acquisition signal is electronically processed and presented to the gunner as an audible signal. The audible signal clarity and intensity is directly related to seeker acquisition of the aircraft. The gunner must discern the audio signal as soon as possible to permit early engagement of incoming aircraft. This requires the gunner to hear low level signals in contrast to background noise.

Infrared is the band of wavelengths in the electromagnetic frequency spectrum just below visible light (see Electromagnetic Spectrum illustration). All substances radiate IR energy, the amount depending largely on their temperature. IR energy has properties similar to light; that is, it travels in a straight line and at the same speed as light. The missile senses IR emitted by a target by optically focusing this energy on the surface of an infrared detector in the missile seeker system. The detector cell is cooled by the coolant in the BCU. When the seeker acquires the IR energy emitted by a target, acquisition signals are produced by the weapon which inform the gunner that the target has been detected.

The atmosphere is not completely transparent to IR. Certain gases in the atmosphere, primarily carbon dioxide and water vapor, absorb energy in the IR frequency spectrum. Because the amount of carbon dioxide in the air is fairly constant, its effect on detection range is consistent and need not be considered by the gunner. Water vapor content varies widely with geographic location and local weather conditions. The sun's IR is also reflected from objects, causing these objects to become secondary sources of background radiation (false targets). Typical secondary sources are bodies of water, bare hillsides, and white clouds. Some sources of secondary background radiation are shown in Background Radiations illustration.

The Stinger IR seeker can discriminate between radiation from a small point source, such as the tailpipe of a jet, and large background sources, such as clouds and terrain. With the exception of the sun, the engine exhaust or tailpipe of the target is usually the smallest and hottest object in the environment and, therefore, will be tracked by the missile seeker.

ACQUISITION

When the target provides sufficient IR to the seeker, an acquisition signal is generated. This signal indicates that the seeker has acquired the target. Two conditions are required for the missile seeker to acquire the target's IR. The weapon must be activated and pointed at the target and the IR from the target must be strong enough to activate the acquisition indicator circuits.

Listen for distinct acquisition tone (and discriminate between target and background, if necessary). If the weapon is aimed away from the target when the gyro is caged, the tone should decrease.

UNCAGING

After insuring that the seeker has acquired the aircraft, press the UNCAGING switch with the thumb, hold it in, and continue to track the aircraft. After uncaging, the IR tone usually gets steadier and louder.

This lets the gunner know that the seeker has locked onto the aircraft and is tracking it. If the tone does not get louder upon uncaging, release the UNCAGING switch and continue to track the aircraft in the range ring, allowing it to get closer. Then press the UNCAGING switch again.

If the IR tone is weak or distorted, the seeker may be locking on the background instead of the target. When target IR cannot be acquired, or when trying to separate target IR tone from other tones (because of the background radiation), sweeping the target or the figure eight (8) method should be used.

When the target is low on the horizon, sweep the target looking through the front sight ring. Swing the weapon in U-shaped movements through the target until the IR tone gets stronger. A clear tone should be received when the aircraft enters the range ring on the sweep (see illustration below).

When the target is farther above the horizon, use the figure 8 method. Move the weapon, using the target as a starting point, and make two loops as in a figure 8. If IR still cannot be acquired, keep "figure eighting" until the IR tone from the target gets strong enough to lock on to. Always verify tone, when a target is near a background IR source, by one of these two methods before uncaging the gyro.

SUPERELEVATION AND LEAD

Superelevation is the elevation angle that is added to the missile line of sight. This angle compensates for the effects of gravity on the missile prior to flight motor ignition. Lead is the angle between the point of aim and the target. Right or left lead is required for all targets except those fixed-wing targets directly incoming or outgoing.

The following explains in words and figures how to place the target within the rear sight reticle prior to firing.

ADDING SUPERELEVATION

First, to superelevate, raise the front of the weapon A.

Then, move the aircraft from the range ring B to either the left, center, or right lower reticles C, D, or E.

RIGHT LEAD INDUCED (FIXED-WING)

All fixed-wing aircraft and helicopters coming from the left, or slightly from the left, are placed in the left reticle C.

INCOMING/OUTGOING (FIXED-WING)

All fixed-wing aircraft directly incoming or outgoing are placed in the center reticle D.

LEFT LEAD INDUCED (FIXED-WING)

All fixed-wing aircraft and helicopters coming from the right, or slightly from the right, are placed in the right reticle E.

LEFT LEAD INDUCED
(HELICOPTERS AND HOVERING VTOL AIRCRAFT)

Directly incoming/outgoing or hovering helicopters and vertical take-off and landing (VTOL) aircraft are placed in the left lead reticle. Placing an incoming/outgoing or hovering helicopter in the right lead reticle is acceptable, but not recommended.

FIRING

Before pressing the firing trigger, make sure that IR tone can still be heard. While still pressing the UNCAGING switch, squeeze and hold the firing trigger. Keep tracking the target until the missile lanuches. Release the trigger and uncaging switch 3 seconds after launch. When firing, hold your breath until you release the trigger so as to avoid inhaling toxic fumes. If the exhaust plume visibly persists at your position, move away from the plume before breathing again (reference TM 9-1425-429-12).

Post firing procedures include the following:

A hangfire is a delay in the functioning of a weapon-round. It can last up to several minutes. A misfire is a complete failure to fire. If a missile does not fire, the following steps should be taken:

A dud is a missile whose flight motor does not ignite. It is ejected from the launch tube assembly, travels a short distance, then falls to the ground. In this case, also, mark the location and then call the EOD unit. Remember the missile is classified and should not be left alone.