Piper Flyer Association - Technical Know-how, Serious Fun read more


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October 2005/

It is the mildest of weather conditions facing pilots, and yet it can be the most deadly. It creeps in on "little cat's feet" but can make even the most expensive airliner or business jet go someplace else rather than face it. Like an in-law, it comes sometimes when it isn't predicted and seems to never leave—at least, not on your schedule.

Fog doesn't sound like much of a problem until you are flying above it, are running low on fuel and hoping it will go away before you hear silence instead of your engine. I have dealt with all kinds of fog with all kinds of aircraft all over the world.

The most frustrating thing for me and possibly for you is the fact that you can often see right up through the stuff and still don't have the visibility to be legal or safe. Most low visibility instrument takeoffs I've done with the airline resulted in us being in the clear above the fog well before our landing gear was up and in the wells. So... what is the danger of going ahead and taking off when you know you'll be on top or at least think you will?

Simply put, when you are operating in fog, you can't see. I know that sounds terribly simplistic, but you'd be surprised how many pilots, especially VFR only pilots, every year try that little takeoff in the fog trick and end up running into things on the ground or discover that the fog actually doesn't end at 200 feet—it goes up to 35,000 feet.

Point is, you can never really tell with fog. Fog, while being a quiet, white thing of poetry and drug overconsumption is the most discussed and debated item every year when I go to recurrent training at the airline.

The main question for us airline guys? Legality. Depending on how your aircraft is equipped, how you are rated, what kind of experience and training you have and the details of the runway you are trying to use for takeoff, the minutiae of what constitutes a "legal takeoff" can baffle the most experienced pilot. Just following the guy ahead of you won't make you legal—and just because you are legal, does that guarantee that you are safe?

Back to the 1950s
One of the gifts my old flight instructor, Jesse Hinson, left me was his copy of Theory of Instrument Flight by the Department of the Air Force. It was published in 1954 and I'm sure Jesse thought, "What the heck, this kid is never going to do any real flying anyway... I'll just give him this old book."

It turns out I've been reading this tome for over 30 years now and a lot of what is in it is still perfectly reasonable and usable. Not the part about flying in and around thunderstorms, though.

Hang On!

The Air Force's advice for thunderstorm penetration? (That's right, I wrote "penetration"—they didn't have much airborne weather radar in those days and the mission had to be accomplished, right?)

"In general, thunderstorms in the form of turbulence, blinding lightning, icing, 'heavy' rainfall and high winds, present very definite hazards to flying.

"A pilot with basic knowledge of thunderstorm activity, however, should be able to cope with such hazards."

I guess I wasn't that pilot because the first time I accidentally penetrated a storm in a 172 the engine quit, the prop stopped and my seat needed to be replaced.

Fog in the '50s

During the age of the real "Fonz," fog was the same thing it is today—a pain in the butt. According to the Air Force of June Allison and Jimmy Stewart, "Fog is a suspension of minute water droplets, or ice crystals when the temperature is substantially below freezing in the atmosphere with no apparent downward motion."

The Berlin Airlift Boys continue: "Fog is generally more prevalent in coastal areas, where more water vapor is available, persistent in industrial regions because of the high concentration of condensation nuclei, but also frequently forms when the relative humidity is less than 100 percent. In most areas of the world, fog occurs more frequently during the colder half of the year than the warmer half."

Modern, Space-Age Fog

Fog today is the same stuff that shrouded James Bond when he left M's office in London to go out and kill his first super villain.

What made the fog happen and what type of fog you are dealing with is more important to you than James, because knowing that information will be what tells you when the fog is going away. This information is more valuable than having "sharks with friggin' laser beams glued to their heads."

We'll quickly review the types of fog and then get back to our kick-butt James Bond metaphor:

• Radiation Fog
is formed by the cooling of land after the sun goes down by thermal radiation when the skies are calm and clear. The ground, cooler than the air, produces condensation in the surrounding air by heat conduction.

It can be less than three feet deep but slight turbulence in the surrounding air can make a thicker layer. Radiation fog usually occurs in the autumn and sunrise usually solves the problem by burning it off.

• Advection Fog
happens when wet air passes over cool ground by advection (wind) and is cooled. It is common at sea when tropical air runs over cooler water. You'll probably see it in your flying travels when a warm front passes over an area with a significant snowpack.

• Steam Fog
is caused by cold air passing over warmer water. You Chicago pilots know of this sort of thing and call it "lake effect snow" or "lake effect rain." Lake effect fog is the same thing and can also show up as hoarfrost or freezing fog.

• Precipitation Fog
(or frontal fog) comes to be as precipitation falls into drier air below the cloud, the liquid droplets evaporate into water vapor. The vapor cools and at the dew point it condenses and fog forms. I have never seen this type of fog, even out West in the desert, unless I mistook it for virga.

• Upslope Fog
happens when winds blow up a slope (called orographic lift). It cools as it rises and the moisture condenses into fog. This happens sometimes on mountaintops which explains some of the out-of-control runs I've had at Park City, Utah.

I think for the purposes of operating your aircraft, we can eliminate precipitation fog and upslope fog from our list of problems. The possible trouble you'd have with precipitation fog are overshadowed by the precipitation itself and if you are flying around upslope fog, I suggest you worry more about the mountain and less about the fog.

Radiation fog is like watching reruns of "Sex in the City." No matter how much it bores you, you'll just have to wait it out if you want a successful date (or flight). The bad news is that if that fog is there at night and you are too, it will most likely win the battle of wills. If you are there in the morning and see radiation fog, you can count on the sun to burn it off.

The question then becomes not how, but when. In my experience this "wait for the fog to burn off" is inversely related to how badly you want to leave. When I am standing-by in an aircraft for which I am being paid by the minute, the stuff burns right off. If I'm in a hurry to get my rental 172 back before they charge me another three-hour-a-day minimum, it'll hang around until noon.

With advection fog, you have the added variables of wind and weather to either help or hinder your escape. The same wind that brought you the fog off of Lake Michigan can shift and blow it away.

What are your Minimums?

The minimum visibility you must have for takeoff varies for each airplane and pilot and what part of the FARs you are operating under. That would take another article and like I mentioned about recurrent, we'd never agree anyway. Just fly safe, okay?

Landing minimums in fog are also a variable thing based on your operation. Before you go in to "take a peek" remember that not only is that a stupid thing to do, the FAA is getting more serious about enforcement—and fog and visibility is something the FAA can quantify. Bureaucrats love things they can quantify. You'd lose.

The Final Bond Metaphor

The fog that 007 stumbled out of MI-6 into his Aston Martin is just as deadly as the thunderstorms that those gallant cold warriors flew their Century Series fighters through. Fog is more insidious though, because many pilots think they can beat it.

Think again, please. There is nothing in your life that is so important that it won't wait for an hour as the fog burns off and you leave VFR instead of in an ambulance.

If you are already in the air and fog starts to form below you, find a place to land now.

Morning fog sometimes takes more hours to burn off than you have fuel in your tanks to out-wait. Landing at an airport short of your fogged-in destination beats being picked out of a tree by a fireman named "Bubba."

There is no dishonor in a strategic retreat—and even if you break an FAR or two in order to land safely, it is a much better deal.

Jesse Hinson Has the Final Word

When it comes to legalities versus safety, my flight instructor, Jesse Hinson, said it best: "It is better to be judged by 12 men than carried by six."

Kevin Garrison's aviation career began at age 15 as a lineboy in Lakeland, Fla. He came up through General Aviation and is currently a senior 767 captain. When not frightening passengers, Kevin plays tennis and lives on a horse farm in Kentucky, where he writes unsold humor projects and believes professional wrestling is real and all else is bogus

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