Beyond the Checkride by Howard Fried & Gene Gailey

Author:Howard Fried & Gene Gailey
Language: eng
Format: epub
Publisher: McGraw-Hill Education
Published: 2014-03-12T16:00:00+00:00

Fog—Sometimes It’s Almost Predictable

Fog, which severely limits visibility, can be among the worst weather hazards a pilot may encounter. Here in the Great Lakes area where I live, every fall (usually about mid-October) and every spring (usually in March) we get a period of four or five consecutive days when we get to hear that rare term, “zero-zero” at many of the local airports. We get this in the morning, starting about sun-up and lasting until almost noon, by which time it has burned off.

In the discussion of icing earlier in the chapter, I mentioned the fact that the instrument pilot pays close attention to that little round dial which tells him or her what the outside air temperature is. Most pilots also pay close attention to the temperature-dewpoint spread at the surface, or if not, he or she certainly should because it is literally impossible to land if there is fog lying on the ground at the destination. Robert Buck, in Weather Flying, has this to say about dewpoint:

There are a couple of items that pilots should know. One is dewpoint. Most of us know it as the temperature at which condensation begins. If the temperature is 50 degrees and the dewpoint 45 degrees, we have only to cool the air 5 degrees for the moisture to come out where we can see it … and if it’s fog, that’s all we can see …

Sometimes fog doesn’t form until the sun comes up. An airport may have the same dewpoint and temperature all during a still night and yet not fog in. Then, just as the sun is coming up and we think everything will be okay, the airport goes zero-zero in fog.

In discussing the weather requirement for filing an alternate with instrument applicants, I always point out that there will be occasions (although rarely) that a given flight will be impossible because of the fact that there will be no legal alternate within the range of the airplane. This is the one situation where the airlines have the fuel reserve advantage over those of us who fly general-aviation airplanes.

I fly out of Pontiac, Michigan, and there have been times when I have filed for Chicago and had to list Pittsburgh as my alternate. But there are occasions where the entire eastern half of the country is socked in, from St. Louis to the Atlantic Coast. When this situation prevails, we are simply stuck, but United Air Lines can file from Detroit to Chicago and list Los Angeles as their alternate.

Like ice, fog is interesting stuff. I remember one time holding over the outer marker in absolutely clear skies with great visibility when my destination airport, about five miles away, was covered with ground fog about 100 to 200 feet thick. I was behind schedule for picking up a passenger, but I held for about a half hour, waiting for the fog to burn off. Finally, I could see the runway, and I started down on the approach. I

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