The concept of marginal VFR, sometimes known as scud running, is one of those things everyone shakes their head at and says, "Oh, no. If it's marginal, you shouldn't go." And, in a perfect world, that's a fact. The problem is that it's not a perfect world. If everyone lived in Arizona, no one would encounter marginal VFR (out here it's considered marginal when visibility drops below 20 miles), but that's not real life. In far too many parts of the world, a CAVU day"ceiling and visibility unlimited"is an extreme rarity, and haze, clouds, fog, and other icky stuff are standard fare.
In some places, like much of Alaska during the winter, it's common - necessary, actually - to fly VFR beneath low clouds during the winter. There, IFR flight is not an option for piston aircraft without ice protection, because they could not safely climb through the persistent low clouds. Also, the visibility there is often unrestricted below the clouds - not a murky three to five miles in haze. Let's discuss marginal VFR and why it should be approached very conservatively, especially by new and low-time pilots.
Although the federal aviation regulations clearly spell out minimums for flight, what is marginal to one pilot may not be marginal to the next, and the difference is often simply what people have gotten used to. In some places, if you don't fly on days with three to five miles' visibility and 1,000-foot ceilings, you won't do much flying. What you call marginal changes as you spend more time floundering around and discover that you actually can get where you're going in less-than-perfect weather. And, therein lives a major gotcha. If you challenge weather and repeatedly win, you start to lose respect for the two factors of marginal VFR that are the most important and dangerous: the lack of predictability and the topography.
Let's discuss the second point first: the topography. Let's be honest - no one ever got hurt by bumping into haze. Haze, mist, or light clouds, as long as they aren't dense enough to cause disorientation, don't hurt. It's the unseen stuff hiding in the haze, drizzle, and clouds that will hurt you. Mountains, hills, and other major pieces of rock may seem to be obvious items to avoid, but some very, very experienced pilots have been lost after running into pointy pieces of real estate that they didn't see coming. If you're down where the FAA seems to say it's OK to scud run (1,200 feet agl, one mile of visibility, clear of clouds), don't think it actually is OK. One mile of visibility is not enough, especially with an airplane that is fairly fast. The faster the airplane is, the more visibility you need.
At 100 mph, you cover a mile in 36 seconds. At 150 mph you catch up with a stationary object in 24 seconds - assuming that you see it coming. Let's say it's one of those monster towers we're seeing a lot of these days. How quickly will you recognize that and react? And what about the harder-to-spot guy wires that radiate out from it?
Look at limited visibility in the same way that your headlights illuminate a two-lane road in the dark. At 40 mph, your lights reach out there and really let you know what's ahead. At 80 mph, however, you might as well have a pair of flashlights to guide you because you overrun your lights so quickly. That's what happens in an airplane: your speed overruns your visibility. One mile's visibility in a Piper Cub is one thing, but in a Beech Bonanza, it's something different. Still, it's easy to get tempted to forge ahead.
And then there's the predictability issue. If you knew that the weather you were seeing at a given moment is exactly what exists all the way to your destination, everything would be cool. You could look around, say, "Boy, is this lousy, but it's flyable," and plunge ahead. Or you could say, "This is over my head; I'm turning around." The decision-making would be easy. But, we all know it's not that way. That's the most dangerous aspect of marginal VFR: We know how the weather is here, but we don't have a clue what's "out there." In that situation, entirely too much of our decision-making process is based on guesswork and the traditional process that says, "I'll go just a little farther and make up my mind then." Is there a way to improve the decision-making?
Common sense says you could call the a flight service station, assuming you're not already so low that you can't raise them on the radio. However, unless the FSS is right on the field you're headed for, the briefer won't know for sure what's happening at your destination airport unless it's a weather-reporting point. Even then, the report could be an hour old. In marginal weather, an hour is an eternity. You need accurate information right now.
The ideal would be to radio the FBO on the field and get a firsthand report, assuming that you're not too low or out of radio range. The next logical option is to go back to the closest airport that you've just flown over, land, and call ahead. It's inconvenient, but it's safe.
When you make your call, you actually want to make two calls. Depending on how long it's going to take you to get there, the questions you have to answer are not only what kind of weather is sitting on the airport now, but also what is the trend? This is where the FSS comes into play. The FBO's estimate of the current weather gives you a solid datum to measure from. Now you can take the surface progs and forecasts from the FSS and apply them to what you know to be the actual case at your destination. Or ask the briefer for the past several hourly observations, if the destination reports weather. This should tell you the single most important thing you want to know: are you flying into improving or deteriorating weather?
Here's a helpful hint from a long-time coward: When they say the weather is due to go down by such and such a time, don't believe them. It always happens before that. If the weather is already marginal, any deterioration will cause some real heartburn, so leave a huge margin. In a close race, always assume the bad stuff is going to get there first and seek safe haven somewhere else.
When you decide to land and call ahead, don't just push the Nrst Apt button and turn to the closest airport if it's off your course, unless the weather is obviously better in that direction. You know what the weather is behind you, and you know whether it's better or not. If you deviate off course without a clear indication that you're going into improving weather, you are playing the same game of "weather roulette" that you were playing with your destination. Flying a longer distance into weather that's known is a whole lot better than flying a shorter period into unknown weather that could be doing almost anything.
Not knowing what's happening in front of us, topographically and meteorologically, is what makes the whole marginal-VFR thing even iffier. At one time, however, that was only half of the equation, because the where-am-I question was always haunting us. In pre-GPS days there was always a huge concern about getting lost when you got down low. The lower you get, the flatter your sight angle is to the ground, so the less you can see. And that's in good weather. Toss in some summertime haze or drizzle and your horizontal visibility becomes limited to a small moving circle with you at its center. These days it's the rare airplane that takes off cross-country without a GPS signal shadowing it. The GPS gives us confidence in our position. But that confidence removes the fear of getting lost, which is a really good reason to treat marginal weather with respect.
Remember, too, that reduced visibility removes an important reality check from GPS navigation. Although many newer GPS receivers, including some handheld units, now offer terrain depictions, most do not - and while the shortest distance between two points is always a straight line, diminished visibility reduces your ability to make sure that straight line isn't trying to tunnel through a mountain.
A comfortable amount of paranoia should always be attached to GPS because it's totally dependent upon some batteries you bought last, uh - well, you can't remember exactly when you bought them. But you have spares. Only they are in your bag on the back seat and you're chugging along at 700 feet, not sure what's in front of you and afraid to let go of the yoke. That's just as well, because if you did find the batteries, you'd have to try to put them in while you're flying and trying to hold the last heading the GPS said was good.
In some ways it could almost be said that a GPS is dangerous in marginal weather conditions because it makes you too willing to poke your nose into places you shouldn't go. If you don't let it affect your how-far-will-I-keep-going judgment, however, it's the greatest thing since sliced bread.
A big question concerning not only the definition, but also the conquering of marginal weather is a function of your experience. When you see marginal weather for the first time, all you see are low ceilings and/or lousy visibility. It's gray. You're not happy. You want to be on the ground. After you've flown for a while, however, you'll learn to read the clouds and weather situation better. You'll recognize those low, wispy, poorly defined ceilings as being totally untrustworthy. You'll be pleased with the well-defined ceiling, regardless of how low it is, because your visibility is better and, if the clouds decide to start down, you can see the trend much sooner and they don't hide as much from you. Also, you'll automatically factor in temperature and know when you stand a chance of picking up ice at the base of some of those clouds. You'll be looking far ahead for signs of snow showers and other precipitation and trying to guess which way it is moving so you know whether to turn toward its nose or its tail to avoid it.
If you know what you're looking at, you can make more intelligent decisions. For the low-timer, the decisions are actually easier because it doesn't take much weather to get him in deep soup in a hurry. The decision to turn around should always be right there on the tip of his mind, ready to be made.
The really safe way to handle marginal VFR is to be sitting on an instrument rating and have a brain box full of current charts and approach plates in the seat next to you. This of course assumes that you are rated and current and the airplane is IFR-capable. If you do decide to file, don't wait until the circumstances have you trying to fly in a dangerous situation.
And speaking of waiting too long: Recognize when everything is going to hell in a handbasket and you're going to have to either go on instruments or land, which is an incredibly serious decision. On the one hand, you're talking about punching up into unknown clouds, not knowing whether there are other aircraft out there and assuming you'll be able to raise someone in ATC to talk you down. It's sheer suicide to think about going up into the clouds, flying IFR for a while, and then finding your way down on your own. Talk about combining blind man's bluff with Russian roulette.
The other alternative is an off-airport landing, which is pretty scary but at least it's something you can control. The really important and tough part of an off-field landing is making the decision to do it. We have a fear of damaging an airplane bred into us, and landing off field is likely to damage the airplane. However, scary or not, remember that you want to survive the landing, so the decision to land should be made by you, not the circumstances. Don't wait until you're forced down to the ground and are out of options. When it looks as if that's what's likely to happen, start looking for the best field or road you can find and make a controlled landing. At the same time, however, at least an off-field landing is likely to save your life; flying into a hill while trying to stay in the air won't.
The safest way to play marginal VFR is to simply avoid it. But, if you're going to fly in marginal conditions, at least set some minimums that you absolutely will not violate. Every minute you're in the air, know exactly where your closest good-weather airport lies. Always have an out and be ready to execute your alternate plan at a moment's notice. None of us likes to be inconvenienced by waiting for weather, but it's a much better alternative than scaring the hell out of ourselves - or worse.
Budd Davisson is an aviation writer/photographer and magazine editor who has written approximately 2,200 articles and has flown more than 300 different types of aircraft. A CFI for 36 years, he teaches about 30 hours a month in his Pitts S-2A Special. Visit his Web site.
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