Pilots that fly at night see some of the most beautiful sights in the world, but there are some biological factors that make seeing things at night — and how you should look for them — very different than seeing things during the day. Whether it is the lights of a New York City out one side and the lights of Philadelphia on the other, or the array of airport beacons visible as you fly over Nebraska at 10:00 pm on a clear winter night, flying at night can provide some real visual wonders — and some very hypnotic distractions to a good visual scan.
Pilots that fly at night have a tendency to become fixated on certain objects in their field of view and this is not a good thing. Reminder: Even if you have filed IFR, you still have the responsibility to maintain visual separation with other traffic — especially in VFR conditions. We must all scan the horizon for airplanes and take action to avoid them.
PRECAUTIONS — To maintain your night vision, the lights in your cabin are typically red or light blue. These colors help to keep your eyes ‘adjusted’ to the night sky. All white lights need to be avoided. The eye reacts to white light sources by dilating to a smaller pupil. The net result is an immediate loss of your night visual acuity, and your ability to spot other traffic.
Defense: If exposure to bright light is unavoidable either before or during a night flight, close one eye. Your eyes adjust to light independently and the closed eye will retain its ‘night vision’ if you protect it.
SCANNING — The best night scan is made in small sections, with special attention paid to your peripheral vision. Focus on a section of the sky for between ten to fifteen seconds and watch for any motion of red, green or white lights that could indicate an aircraft. If no motion is detected, move your focus to the next section of the sky to allow your peripheral vision to cover a different section of sky.
Why: Peripheral vision ‘sees’ better in low light conditions. The center of your field of vision is created by a part of your eye called the fovea, which has evolved to primarily see colors with excellent visual clarity in medium to bright light environments. The *faintest* stars in the night sky will disappear if you look right at them — try it. Look at these objects by casting your gaze to either side by 15 degrees or so. Also, your peripheral vision has evolved to sense motion better — presumably because it needed to get your attention when a sabre-toothed tiger was ambushing you.
SPECIAL CONSIDERATIONS — Hypoxia and fatigue will both contribute to lower visual acuity at night and smoking will exaggerate the effects of both. So be careful and consider using oxygen if it is available — and more liberally. Also, when you spot an airplane at night, monitor its progress only long enough to determine whether it presents a risk to your flight path, then continue your scan to look for other traffic.
The night sky is a beautiful world, but it is a different world. Be aware of the limitations of your body and ACT to compensate for them.
