One of Winter's Flying Traps - Whiteout
Article by Francis Bélanger and Denis Veilleux, published in the November-December 1998 issue of La Brousse, reprinted with permission
As winter approaches, it is recommended that you review particular aspects of what the snowy season holds in store for you. Among other things, it is wise to review your aircraft’s operations manual, check the equipment that has to be carried for winter flights and think about the weather features associated with flying in winter. Besides snow and cold, winter presents a number of new phenomena with which we have to come to terms. One of these is the whiteout. We will focus on this phenomenon, because it holds great risks for the safety of a flight.
(A.I.P., AIR 2.12.7)
"An atmospheric optical phenomenon of the polar regions in which the observer appears to be engulfed in a uniformly white glow. Neither shadows, horizon nor clouds are discernible; sense of depth and orientation is lost; only very dark, nearby objects can be seen. Whiteout occurs over an unbroken snow cover and beneath a uniformly overcast sky when, with the aid of the snowblink effect, the light from the sky is about equal to that from the snow surface . . ."
More simply put, the phenomenon occurs when you are in the presence of a large flat area and the overcast sky blends in with the ground. You get the impression of being inside a bowl of milk or a ping-pong ball. It is impossible to make out the horizon and distance from the ground. Pilots flying VFR therefore lose all the essential clues for continuing their flight safely, even if visibility remains adequate and the ceiling is high.
The phenomenon can be caused or amplified by mist (BR), blowing snow (BLSN) or precipitation in the form of small ice or snow crystals (IC). (See the table of weather codes in the MET section of your A.I.P.)
Here is an excerpt from a TSB accident report:
"The pilot of the C-185 departed in VFR conditions and climbed to 400 ft. AGL. Five miles on, he encountered whiteout conditions over a lake. His instruments indicated a descending left turn. He did not trust them, because he did not feel the turn. When he realized that the instruments were not lying, it was too late. The aircraft hit the ice, and the left wing was sheared off. Fortunately, once all the pieces came to rest, the pilot was unhurt and able to walk away."
Should you encounter such conditions when flying VFR, you would likely suffer spatial disorientation for lack of visual cues. No longer able to see the horizon, you may go into a turn without realizing it. The turn may become a spiral, ending, in the worst case, in impact with the ground. If you do not lose control of your aircraft, you may become one more statistic in the CFIT tables. As it is impossible to determine your altitude visually, slow descent might not be detected before impact occurs. The best-case scenario would be for you to come away with one more piece of experience to your credit as a pilot, without bending metal.
Prevention and preparation
As we have no control over this kind of phenomenon, the only ways to reduce the hazards of whiteout are to:
- Avoid it;
- Recognize it; and
- Trust your instruments.
Avoiding whiteout is not easy, especially if you are flying in areas above the tree line (the limit on mountains and high latitudes beyond which trees will not grow because of the cold). In this case, the weather conditions in which you are willing to fly will be a determining factor. In the areas of the far north it is not easy to fly VFR in completely overcast weather. Discounting the possibility of staying on the ground, an IFR flight would be your best bet to minimize the hazards of whiteout. Unfortunately, this is not always possible. Before deciding to depart, you would do well to analyse weather briefings and forecasts. Do not trust overcast ceilings, even light precipitation and winds stronger than 15 kt. Wind favours the development of BLSN aloft if associated with mechanical turbulence or an unstable air mass. Ice crystals or light snow are then raised aloft and reduce horizontal visibility, producing a whiteout. Note that area forecasts (FA) report only winds exceeding 20 kt.
If you are operating in areas farther south, below the tree line, you have to distrust the same factors as you would if you were planning to fly over large expanses, such as frozen bodies of water. Whiteout is easily avoided simply by changing course to always keep the treetops, a chain of islands, a road, a railway or a power transmission line within your field of view. These objects will help you to retain sufficient visual clues to perceive depth and determine the attitude of your aircraft.
Careful study of the proposed route will help you to determine the kind of terrain and obstacles that you will be flying over. You will be able to identify places where the whiteout phenomenon would be likely and to alter your route to avoid areas that you believe to be risky. The sacrifice of a little time and fuel is really a very small price to pay to ensure a safe flight.
Despite all the precautions in the world before your flight, and even if you stay alert during the flight, you may still encounter whiteout conditions. The phenomenon could be manifested in various signs, depending on your experience and the phase of flight. Disorientation (see A.I.P., AIR 3.9), loss of the sense of balance, nausea and the feeling of having entered an all-white envelope are all possible sensations. You may also not experience any sensation at all, and that is where the greatest danger lurks. If you are qualified for VFR only and briefly consult your instruments, you may have the same reaction as the pilot in the example given above. As your vision and centre of balance no longer provide you with accurate clues, you will tend not to believe what your instruments tell you. This is a normal reaction because your piloting skills are based mainly on VFR and "flying by the seat of your pants." If you should find yourself in such a trap, what should you do?
Regardless of the situation you encounter, it is always important to keep your head. First, it is essential to be willing to use your instruments to help you, even if they seem to be wrong. I am assuming here that they were in good working order on departure, and that you are unable to pass over to IFR. Here is how to proceed:
- Consult the attitude indicator - Keep the wings parallel with the ground and fly level.
- Note the altitude - Make sure to establish yourself at a high enough altitude to cross obstacles without danger.
- Check your heading - Maintain a heading that will take you to terrain or ground presenting objects that you can distinguish.
Turning back might be an option, but I recommend it only if weather conditions seem to be worsening to the point of jeopardizing your VFR flight. Such a manoeuvre involves nothing less than making a 180-degree turn without any visual reference, that is, in IFR! Can you perform such a manoeuvre? Each case is unique. You alone can weigh the risks and decide on the best course of action to re-establish a safe and comfortable flight regime.
The whiteout phenomenon is very real, and it has outwitted more than one pilot in the past. Regardless of the type of landing gear on your aircraft and where you fly, this phenomenon can catch you unaware. A good measure of prevention will be your main asset for avoiding whiteouts, with weather conditions and the terrain being the two factors to analyse. If you are unlucky enough to encounter this phenomenon, stay calm and perform minimum manoeuvres. If you have to manoeuvre, do so gently. Changes in attitude should be of the order of 3°. As for banks for turns, between 10° and 15° will be enough.
As winter can severely test your piloting skills, it would be wise to undertake rigorous preparation. We suggest taking a few hours of your time to practice IFR under dual control. IFR is a skill that erodes with time. If you have not done this kind of flying for more than a year, you are probably a little rusty! Remember, the more well-honed tools you have in your chest of pilot skills, the more ready you are to face the challenges of piloting your aircraft.
On that note, good flying and happy holidays!