# Night Flight Techniques Most aircraft training manuals include techniques for night flight with flight related tasks. Visual cues diminish significantly under limited ambient light. The following techniques may be used to supplement those tasks. *** ## **Scanning Techniques** ### **Hover** it is impossible to overstate the importance of scanning during night flight, whether unaided or using NVG. With peripheral vision reduced or eliminated, it can be very difficult to detect aircraft drift. During night flight, aviators use motion parallax to detect drift. Pick an object to the front of the aircraft that is relatively close. This can be a bush, a tree branch of an unusual shape, or some other easily identifiable item. Also pick an object at a greater distance, such as a tower, a light on the horizon or a far tree. If the helicopter is stationary, these objects do not move in relation to each other. Remember that this only shows helicopter movement in two axes. It is important to follow the same procedure 30 to 60 degrees offset from the initial references, such as through a side window, to identify helicopter movement. It is helpful to select one set of references somewhat higher than the other to assist in detecting climbs or descents. The aviator must change their field of view every 3 to 5 seconds, looking forward, then off to one side, then forward again. Use of HUD symbology greatly helps with detecting drift. When hovering in an AH-64 while using the FLIR as the primary flight reference, the aviator must remember that the FLIR is mounted below and in front of the aviator's physical location. This means that the aviator cannot see obstructions not directly in the sensor's field of view. It is imperative that the aviator maintain an aggressive scan and clear the flight path of obstacles before they would normally have to do so. ### **In Flight** Stop-turn-stop-turn motion scanning technique should be used during unaided flight. It is important to stop between the turns long enough to allow your eyes to detect and focus on objects in the environment, For each stop, an area approximately 30 degrees wide should be scanned. The viewing angle includes an area approximately 250 meters wide at a distance of 500 meters. The duration of each stop is based on the degree of detail that is required, but no stop should last longer than two to three seconds to prevent the rhodopsin from bleaching out the image. Figures 4-51 and 4-52 depict the stop-turn scan and scanning with ten-degree circular overlap methods per the following steps: * Ten degree circular overlap viewing should be utilized when moving from one viewing point to the next. Crewmembers should overlap the previous field of view by ten degrees. * Off-center viewing can be used to compensate for the night blind spot (figure 4-53, page 4-50). * View an object by focusing ten degrees above, below, or to either side of the object you are viewing in order to maintain visual reference of the object so as not to bleach it out and lose sight of the object. * Ten degree circular overlap (stop-turn-stop-turn) and off-center viewing are used in combination when flying unaided at night. * Scanning may be faster using NVDs, but the density of the terrain may dictate change to the flight profile or alteration of crew duties to accomplish the assigned mission.
### **Hovering Flight** Aviators may have difficulty hovering at night as visual ground references are not easily seen or identified. The surface type surrounding a hovering helicopter affects an aviator's ability to judge movement. The technique used varies with surface type and any available lighting. An aviator must continually scan to maximize detection of movement and avoid fixation. Many references recommend an aviator drop an item such as a Chemlight to provide a reference. Be very careful doing this, as rotor wash may cause light objects to move, inducing relative motion disorientation. #### **Asphalt or Concrete** Estimating hover height over asphalt or concrete is difficult due to lack of visual cues. An aviator can use markings, such as taxiway lines or centerlines, to provide reference points. These surfaces lack contrast; however, a distinct contrast exists where a hard surface adjoins a soft surface. #### **Grass** Finding reference for precise hovering over grassy surfaces is difficult due to the lack of contrast and absence of visual reference points. Additionally, rotor wash in tall grass creates a rhythmic motion that creates the illusion of movement and can be very disorienting. It is more difficult to hover precisely. An aviator also tends to hover higher than normal or is necessary. #### **Snow** The ability to judge height and determine the contour of terrain is difficult when it is covered with snow. The normal tendency is to estimate altitude as being higher than it actually is and misjudge slope angles. Check instruments frequently. #### **Dust** Hovering in a dusty environment can be very dangerous. Visual references are easily lost and disorientation follows rapidly due to the swirling dust. Use of aircraft systems such as the HUD is strongly recommended. Dust operations are normally trained at the unit. #### **Water** Water is the most difficult surface over which to hover as there are almost no visual references. If possible, the aircraft should be maneuvered near some object, such as a tree stump, or buoy to provide a reference point. Remember that objects floating in the water may move unexpectedly. If waves are present, the aviator tends to drift laterally with the waves. Accurate height estimation requires use of a radar altimeter when hovering over water. Check instruments frequently.
*** ## **Lighting Types and Effects** Aircraft lighting usage should be planned for and briefed. Heavy moisture content in the surrounding atmosphere may make use of the aircraft lighting undesirable. ### **Unaided Flight Position Lights** When hovering unaided with the help of position lights, aviators tend to stare at a single reference point on the ground. When hovering with position lights on "dim," there is a tendency to hover too low, especially in areas with fewer visual reference points. Aircraft control is assisted by configuring scan and using all available information, such as taxiway lights or shadows. ### **NVG Position Lights** NVGs are more sensitive to red lights than green lights. As a result, the side of the aviator's field of view illuminated by the red position light appears more brightly lit than the side with the green light. This causes a tendency to drift in the direction of the red light toward the area of greater visibility. It is very important to use reference points to maintain orientation and ground track when hovering. ### **Landing Light or Searchlight (Aided or Unaided Flight)** When hovering unaided with the help of either of these lights, aircraft movement is more easily detected, but the tactical situation is compromised. The position of the landing light can be critical to the aircrew's night adaptation. If the light is viewed directly, a dark adaptation period is again required for the aircrew. If the light is positioned to provide adequate lighting without viewing the beam directly, dark adaptation can be partially preserved. When hovering at night, references are generally limited to the area illuminated by light. There is a tendency to tunnel vision. ### **Aircraft Anti-Collision Lights** Aircraft anti-collision lights can cause significant disorientation. If the flashing lights create too much disorientation, the pilot in command may consider turning them off according to regulation and local SOP. *** ## **Takeoff** If enough illumination is available to view obstacles, the aviator can accomplish takeoff as a day VMC takeoff. If illumination is insufficient, the aviator should make an altitude-over-airspeed takeoff until the aircraft reaches an altitude that clears obstacles. Takeoff may be performed from a hover or from the ground. The aircrew should treat visual obstacles, such as shadows, the same as physical obstacles. Takeoff from a hover should be performed as an ITO. The aviator on the controls should primarily focus on aircraft control. The aviator not on the controls should crosscheck the instruments as well as providing obstacle avoidance. The lack of visual references during takeoff and throughout the climb may make maintaining the desired ground track difficult. Using the known surface wind direction and velocity assists in maintaining the ground track. Whenever possible, the takeoff heading should be in the direction of the first leg on the flight route as this helps in initial orientation, especially during low illumination. If the landing light is used during takeoff to detect obstacles, the illuminated area increases in size as altitude increases. As soon as possible, the landing light should be extinguished to aid vision. When the landing light is turned off, the aircrew can expect some reduction in night vision. Takeoffs in severe dust or snow conditions are extremely hazardous as ground references are likely obscured.
*** ## **En Route** Route planning for night flight is similar to instrument flight planning due to limited visibility. Planners must provide aircrews with obstacle clearance while navigating in low ambient light levels. Scanning aircraft instrumentation becomes extremely important to avoid special disorientation. ### **Unaided** After reaching the desired flight altitude, allow time to adjust to flight conditions. This includes readjustment of instrument lights and orientation to outside references. During the adjustment period, the aircrew's night vision continues to improve until optimum night adaptation is achieved. Remember to allow additional time and distance as necessary to allow for reduced ability to identify landmarks and obstacles. ### **Aided** The viewing distance increases with altitude. Turn radius and aircraft separation must take the 40-degree field-of-view of ANVIS and HDU into account. ### **Overwater** Long flights over water without a visible horizon should be avoided. Before flying overwater, the barometric and radar altimeters should be checked for proper operation. Aviators should set the radar altimeter low altitude indicator to the minimum acceptable altitudes. Due to the loss of visual references, the aircraft appears to stop in mid-air. As a result, there is a tendency to lower the nose of the aircraft. The aviator not on the controls should maintain a cross-check of the flight instruments to prevent inadvertently flying into the water. Trail aircraft should monitor and advise the flight if any aircraft appears to be descending below the briefed altitude. *** ## **Landing** Due to reduced visual capability at night, pilots should select larger LZs for night/NVG operations than those used in the daylight. At night, LZs should be relatively clear of obstacles on approach and takeoff paths. During an approach without aircraft lights, aviators should observe the contrast between the dark trees and the lighter open area, as this aids in identification of obstacles along the LZ boundary. Altitude, apparent ground speed, and rate of closure are difficult to estimate at night. Throughout an approach, other crewmembers can provide information to the aviator on obstacle avoidance, altitude, airspeed, and approach angle. Maintaining a thorough scan, including the side windows, aids in estimating such information as the rate of closure. If aided, use of HUD can help greatly with rate of closure. If approach is made to tactical lights, aircraft drift can be detected by the relative position of the aircraft and the lights. Except in blowing snow or dust, night approaches to an unlighted area should be terminated at a hover and followed by a slow vertical descent to the ground. Approaches can be made to the ground or terminated at a hover. Approaches to the ground require the most skill and proficiency. Field LZ approaches are normally planned to terminate at a hover because it is difficult to determine the surface condition. However, if the LZ surface can be adequately assessed during approach, an aviator may continue to the ground. Each approach must be separately evaluated. As the aircraft nears the ground, it is difficult to predict when ground contact will be made. To avoid slowing the vertical descent excessively and over-controlling the aircraft while waiting for touchdown, an aviator should reduce collective gradually and continuously. *** ## **Dust Landing** Under NVD, it is impossible to determine how much dust or debris is stirred up during landing operations. This is true even when the aviator has landed in the same location within the past few days. It is impossible to know what may have changed (for example, grass may have been mowed or the ground may have dried out). Perform every landing as though into dust or other degrading condition, and be prepared to abort the landing if necessary.
*** ## **Ground Lighting Aids** A field lighting system provides fewer visual cues than a lighting system for a fixed landing site. Approaches to a field LZ normally are made without a landing light. The type and arrangement of lighting may vary considerably. Regardless of the lighting device, at least two lights should be used, separated by at least 15 feet, to identify the touchdown point. An illusion of movement (autokinesis) may occur when a single light source is viewed. When more than two lights are used to mark the LZ, spacing between the lights can be reduced. Two tactical field lighting configurations are used as landing aids for aircrews—the inverted Y and the T. When operating with NATO aviation forces, aircrews should anticipate use of the T. ### **Inverted Y** The inverted Y system is best used for an approach initiated from terrain flight altitudes. The Y is a landing reference. It may not have been set up by aviation personnel, and may not reflect a safe approach path for the aircraft. It may be desirable to land the aircraft to the left of the centerline at a shallower than standard angle due to prevailing conditions. Figure 4-57, page 4-54, depicts the inverted Y system.
Before the aircraft reaches the entry point for approach, lights in the stem may appear as a single light. This sight picture also indicates the helicopter is on approach and below the desired approach angle. When the normal approach angle is maintained, the Y appears normal. If the distance between the lights appears to increase, approach is too steep and the helicopter is above the standard approach angle. If the distance between the lights appears to decrease, approach is too shallow and the helicopter is below the standard approach angle. If the spacing between the front lights is uneven and the stem is shifted right of the centerline, the aircraft is to the right. If the spacing between the front lights is uneven and the stem is shifted left of the centerline, the aircraft is to the left. The desired touchdown point is inside the Y with the fuselage aligned with the stem lights. During the last 25 feet of the approach to a Y, aviators should divert their field of view away from the lights and concentrate on acquiring ground references. Figures 4-58 through figure 4-63. {% tabs %} {% tab title="4-58" %}
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{% endtab %} {% endtabs %} *** North Atlantic Treaty Organization -T The T, while seldom used by United States forces, may be encountered when working with allied forces (figure 4-64) . The T is best used for approaches initiated from an altitude above 500 feet AGL. The apparent distance between the lights in the stem of the T can be used as a reference for maintaining a constant approach angle. A change in the spacing of the lights occurs as the approach angle changes. If the distance between the lights appears to increase, the approach angle is becoming too steep and the helicopter is above the desired angle of descent. If the distance between the lights appears to decrease, approach is becoming too shallow and the helicopter is below the desired approach angle. If the stem of the T points left of the helicopter, the aircraft is too far right of the course and should correct left. If the stem points right of the helicopter, the aircraft is too far left of the course and should correct right. During the last 25 feet of approach to a T, aviators should divert their field-of-view away from the lights and concentrate on acquiring ground references.
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