NVG Operations Trivia #21-40

The following 60+ questions, posted in 20 question sets, focus on NVG operations.

21. Q: How do you accomplish interpupillary adjustment?   
    A: Close one eye and adjust up/down, left/right so that the diopter ring is balanced (if the ring appears wider in one quadrant, the lens is not centered on the eye)

22. Q: ANV 20/20 focusing process? 
    A: Hold the on button and you should see the BATT CONDITION OK light and AMBIENT LIGHT OK green lights illuminate. Focus on the high light setting should yield 20/30 (according to the operator’s manual), 20/25 (according to CG courseware – ICW). Low light should yield 20/40. You only need to be able to determine the lines of the grid to determine that the NVGs are focused to that acuity. Every line on the grid may not be perfectly clear.   

23. Q: What are potential image defects?  
    A: Shading, edge glow, bright spots, dark spots, distortion, honeycomb, chicken wire, veiling glare.  

24. Q: What are NVG “grounding” disreps?  
    A: Shading, edge glow, flashing, flickering or intermittent operation (can be remembered by the letters SEF). As well as any of the potential image defects that create a loss of acuity or a distraction.  

25. Q: What is field expedient focusing procedure? 
    A: Focus using sharp edges and corners of an object (usually man made) at about 100-200′.  

26. Q: LED lights outside the invisible spectrum? 
    A: Illumination wavelength may be outside the NVGs’ sensitivity range. Be aware obstacles may appear unlit. Have unaided crew members call out obstacles. Look under and around NVGs. Report non-compatible LEDs to the FSDO and FSO.  

27.  Q: Compensation for reduced field of view? 
    A: You need to scan to compensate for the reduced field of view. This will also help with closure rates, depth perception, and undesired aircraft movement.  

28. Q: Fixation challenges? 
    A: Fixation results in a loss of SA to include closure rates, aircraft attitude/orientation and aircraft movement. Pilots need to scan the instruments and include other objects and/or the horizon when able.  

29. Q: What is illusory motion (also known as vection)? 
    A: The perception the aircraft is moving due to objects near the aircraft moving (rotor wash over water, snow, dust and tall grass). The lack of peripheral cues exacerbates this condition on goggles.   

30. Q: What cues allow distance estimation? 
    A: The TV screens make it difficult to perceive distances. The cues we rely on to perceive distances are size constancy, motion parallax and flow, shadows and shape of linear perspective.  

31. Q: What is motion parallax? 
    A: Closer stationary objects move faster than those farther away. This is the most important monocular clue for estimating distance.  

32. Q: What is linear perspective? 
    A: Parallel lines converge as their distance from the observer increases.   

33. Q: What is vertical perspective? 
    A: Objects farther away from the observer are higher on the horizon than those closer to the observer. This can only be used with surface-based objects. Objects such as aircraft and tall towers need other cues to discern distance.   

34. Q: What is shape constancy? 
    A: The brain can perceive an object as changing shape with changes in the angle, orientation, or, perspective from which it is viewed.  For example, a circle viewed from an angle turns into an ellipse. If you know the shape of an object you are observing is a circle you can determine the angle you are seeing the circle from.

35. Q: What is size constancy?   
    A: The only perceiving an object of a known size can help estimate distance. For example, the size of cars on the road help is perceive distance from the road.  

36. Q: What is the relationship between distance and the size of an object? 
    A: The closer you get the bigger it gets. Closure rate can be judged by how rapidly the size increases. For example, on an approach to a ship’s flight deck the rate at which the size of a ship increases give clues to the rate at which you are approaching (you often need to be near the object for this to be effective – for example 300’ from the flight deck of the ship).

37. Q: How does distance affect the variations in shading and detail of an object?  
    A: More detail is evident as you get closer (e.g., a hill side may look uniform  from a distance, as you get closer you see contour variations and more vegetation  detail).  

38. Q: Challenges of distance estimation to light sources? 
    A: The brain’s assumption is that the brighter the light, the closer it is. This should NOT be used on NVGs. The variation in light intensity and brightness can be misleading.  

39. Q: How do false horizons affect attitude? 
    A: Particularly with the loss of the natural horizon, false horizons can lead to spatial disorientation. Use your instruments to back up your perception.  

40. Q: What is the relationship between motion and spatial disorientation? 
    A: When there is a lot of “flow” information and then not much at all, the body perceives a slowing of the aircraft (e.g., going feet wet over a large calm lake). When there is less flow information, the body perceives an increase in airspeed (punching into the bottom of clouds or a rain/snowstorm). These illusions require a strict instrument scan to overcome.