Flight Training - October 2011 - 33

A HALFHOUR IS A LONG TIME TO FLY SEMIBLIND THROUGH THE NIGHT.
DURING THE DAY, your vision is best directly in front of you, thanks to the cones that are centered on the back of your retina. At night, rods do the work, and since they are offset from the center, peripheral vision is preferred.

A half-hour is a long time to fly semiblind through the night. Slow down, let your eyes adapt to the darkness, keep your cockpit lighting low, and avert your eyes from bright lights that might adversely affect the physical process of adapting to the darkness. Remember, while it takes our eyes as much as 30 minutes to adapt to the dark, looking directly into a bright light can reset our eyes back to daylight mode in a mat-

Even dim lights can tend to flicker or go out, when we look directly at them in the darkness. This anomaly of optical clarity occurs because our eyes register light using different sensors in low light than the ones they use when operating in bright light. Those low-light sensors, called rods, work well. However, their physical arrangement within the eye leaves a blind spot that can be tremendously frustrating to compen-

DAY the street, it’s good. That ability to quickly adapt to light keeps you from walking into the street, where you might be run over by a car. On the other hand, if you were sitting in the cockpit all acclimated to the dark, and you were to inadvertently stare into the landing light of another aircraft taxiing nearby, your night vision could be affected considerably. You would have to begin the process of acclimating to the darkness all over again. That’s where the 30 minutes comes into play. It can take up to 30 minutes for the eye to fully adapt to the low light levels available at night. That sluggish rate of adaptation suggests that pilots should think carefully and conduct themselves with caution when preparing to fly at night. After sunset, it’s not a good idea to walk directly from a well-lit FBO out onto the ramp, climb into the airplane, and fire up the engine. While the instruments may indicate all systems are in the green, our own systems are not. Our eyes will still be adjusting to the darkness when we leave the ground—which will leave us unable to reliably distinguish between the lake we normally rely on as a landmark, and the mountain up ahead. ter of seconds—forcing us to repeat the entire process. In the cockpit we can prevent ourselves from unintentionally ruining our night vision by taking some basic precautions, and thinking about the environment we will be operating in before we ever leave the ground. A flashlight fitted with a red lens can go a long way toward preventing our eyes from being exposed to light that will adversely affect our night vision. However, that red lens will cause any red marks you’ve made on your sectional chart or note pad to disappear. Make sure your marks and notes are in black ink so they will show up clearly under the less intense, rose-colored lighting offered by your modified flashlight. Another aspect of night vision that is not well understood by student pilots is the blind spot at the center of our field of vision. While we have a tendency to look directly at something that attracts our attention in good lighting, that practice can be problematic when flying at night. In fact, looking directly at an object at night can tend to make it disappear, or become less distinct.

NIGHT

sate for if you aren’t aware of how the eye works at night. The best way to see an object more clearly at night is to look near it, but not directly at it. Moving your gaze five to 10 degrees from the object makes it easier to see, track, and identify an object at night. Darkness can lead to a wide variety of optical illusions that can cause us to make errors in the cockpit. Even something as seemingly simple as picking out the horizon can be a challenge at night. Dots of light on the ground can be difficult to differentiate from the dots of light given off by stars. This can result in a false horizon illusion that can cause a pilot to misalign the aircraft in flight, pitching or rolling into an unusual attitude based on the assumption that the aircraft is oriented correctly to a horizon that isn’t really the horizon at all. Proper training can help us to overcome the limitations and illusions that come with night operations. Many have come before you, and they found a way to work well in the dark.
Jamie Beckett is a flight instructor and author based in Central Florida.

OCTOBER 2011 FLIGHT TRAINING

/ 33

Flight Training - October 2011

Table of Contents for the Digital Edition of Flight Training - October 2011