July 2001Features

Over The Top

The Pros And Cons Of Flying VFR Above The Clouds


VFR over the top - flying VFR above a layer of clouds, even a solid layer, and it's perfectly legal. Is there any flight condition that can solve so many problems while, at the same time, setting you up for so many others? And then there's that feeling of insignificance, just a tiny machine alone above a field of endless white, a serene view spiced with an endless stream of nervous thoughts like, "Where am I? What's the weather ahead? How do I get down from here if the forecast is wrong? Where is the nearest restroom? Did the engine just miss a beat?"

Before going any further, we should make a clarification. VFR over the top is different from VFR on top, but you'll often hear the terms used interchangeably. To fly VFR on top, you must be an instrument-rated pilot on an instrument flight plan and request a VFR-on-top clearance. (To complicate matters, this is sometimes called IFR over the top.) This allows you to climb through clouds to VFR weather above them. You don't need an instrument rating or any kind of special clearance to fly VFR over the top. Instead you must conduct your entire flight under VFR conditions following VFR rules even though some of the time you may be above a solid layer of clouds and unable to see the ground.

Clouds are nothing but water vapor. We all know that. Still, they are the bane of a pilot's existence. When they are hanging low above a blanket of not-so-hot visibility while unlimited visibility and sparkling blue skies beckon through holes from above, we're subjected to a terrific temptation: Why not paddle up through a hole and cruise along in the sunshine where we don't have to worry about running into things? And that thought actually does make sense. Many times taking the high road is the safe thing to do, but there are some huge - really huge - caveats attached to that concept. For one thing, old man Newton wasn't kidding when he said that everything that goes up must come down. And therein lies the crux of the entire VFR-over-the-top question. Can you get up easily (and legally), and are you absolutely guaranteed of being able to get down safely (and legally)? These are the big two in terms of items to worry about while trundling along on top, but other worries abound, like knowing where you are and what you'd do if the engine failed.

For the most part, the federal aviation regulations (FARs) take an indirect approach to VFR over the top. Definitions of VFR weather and required cloud clearances define the limits of VFR over the top as much by what they don't say as by what they do. The old rule about maintaining cloud clearances of 500 feet under, 1,000 feet over, and 2,000 feet horizontal pretty much determines how big the hole has to be to get up on top, as well as how big it has to be to get back down. That 2,000-foot horizontal clearance means you're looking a hole that is more than three-quarters of a mile across, which is a pretty big hole. The definition of a legal-sized hole is not simply a break in the clouds that lets you see blue or brown ahead. Legalities aside, sneaking through a tiny hole has some other disadvantages we'll discuss later.

Also, there is VFR over the top and then there is VFR over the top, the difference being what you're over the top of. Is it a light cloud deck with lots of breaks or a solid sheet of white stuff that extends from where you are to where you want to be? The regulations don't address this, and you have the option of flying over either, although sound judgment should stop you from doing so in some cases. Just because it's broken when you drive up through it, doesn't guarantee that it's going to stay that way along your route. Remember, you're moving a couple of miles per minute, and cloud cover can change quickly with distance.

What the regulations do address in detail is the equipment your airplane must carry to operate VFR over the top. FAR Part 91.507 requires aircraft used in over-the-top operations to be equipped with the same instruments and other equipment required for instrument flight. Except for that, it's more or less up to you. As you decide whether or not to go over the top, there are some conditions you'll need to consider. Besides the extent of the cloud coverage, you have to try to read what the clouds are doing. For instance, you would be amazed at how quickly cumulus clouds can grow from cute little puffies to towering monstrosities with no room between their bases to let you back down. Also, cumulus clouds are never just lying there like stratus clouds. They are actively sucking in energy and building. Because of that, even if you're flying a fair-sized, high performance airplane there's one basic fact you must remember: When challenging building clouds, an airplane will eventually run out of energy and be able to go no higher, but, for the sake of this discussion, a cumulus cloud has an unlimited amount of energy to draw on and can climb as high as it wants.

In case you haven't picked up on the negative tone, let me clarify: VFR over the top is not something to be approached casually. In fact, it's really helpful if you approach it with a combination of pessimism and out-and-out paranoia. Always assume the worst, and plan accordingly. Part of that planning is to stack everything in your favor ahead of time by knowing everything there is to know about the weather en route, at your destination, and at alternate airports along the way. This is especially true if you're going to be over a fairly solid cloud mass for any length of time. You don't want a nasty surprise waiting for you at the other end.

What you're looking for in the weather briefing isn't just what is being reported at that moment but what the forecast is. And don't be satisfied with conditions that are forecast to do anything but improve quickly and well ahead of your arrival. Even then, be so paranoid that you continually check the weather en route. Be your own weather forecaster, and if you detect a downward trend, start checking your alternates, all of which had better be forecast to be wide open and staying that way.

If the forecast is for the weather to go down after you get there, don't trust it. The only constant in weather forecasting is that it is frequently wrong. Think of the consequences of arriving where the old GPS says your destination should be to find it covered by a solid cloud layer. Always assume that weather is going to bite you in the butt, and plan like a pessimist. Even better, don't fly over any cloud cover that is greater than 50 or 60 percent. Give yourself a lot of margin.

If flying over the top is such an iffy situation, why even consider it? Why not just make it a hard rule not to do it? The answer isn't an easy one, but it is built around a case-by-case situation analysis. Let's say you are leaving home where the weather is deteriorating. Your destination is on the backside of the front and is improving rapidly with everything beyond it already clear. You have a choice of staying home, trying to pick your way between low clouds and the ground, or popping up on top for a relatively short period. Under those circumstances, going high beats going low any day.

Another possible scenario puts you out on the edge of an approaching area of clouds when your destination is somewhere in the middle of the clouds with the front still approaching it. You can get on top easily, but the big question is what's going to happen at the other end. It's going to get worse there before it gets better, and depending on the type of front, it may not get better very quickly. So there's a possibility, actually a likelihood, that the holes at your destination are going to stitch themselves closed, leaving you stuck on top. The odds are against you in this one. Don't gamble. Stay beneath the layer and be prepared to turn around or divert to an alternate if the conditions start to look a little scary. Just remember that there's no place you have to be badly enough to chance making your kids orphans.

One of the more common reasons to get up on top, especially in the western states, is to get up out of the turbulence that always sits right below summertime clouds. In those situations, the clouds stay broken for miles and miles, so it's a good bet you're going to be OK. Besides, you can always drop back down when the holes start to disappear. At the same time, however, clouds that are floating on a layer of turbulence are there because of the vertical atmospheric activity that is causing the turbulence in the first place. If there's one thing that can be counted on in those situations, it's that cloud layers that top out at 4,000 feet at 9 a.m. will be twice as high by noon and out of reach shortly after that. And don't even think about trying to stay on top of a lumpy 10,000-foot solid deck. You won't have the performance or the oxygen to outclimb it if it decides to rise.

In the eastern half of the country, visibility underneath is a primary reason to get on top, but, again, monitor the weather carefully. It's a real bummer to fly down through a hole only to find that the hole goes clear to the ground because the cloud layer went down, not up.

You also have to consider the terrain. In the Midwest, getting back down is usually no big deal as long as the weather meets VFR minimums and you watch out for towers. In the East, bad visibility can sometimes cloak low mountains and hills in such a way that you don't even know they are there until you come out of the hole. In the West, the clouds have an irritating habit of settling into the low places and then developing holes so that you can clearly see the ground below you but you don't realize that ground is in the bottom of a mountain-rimmed valley or wide canyon.

And then there is the question of navigation: If it's a pretty solid deck that prevents you from monitoring ground checkpoints you are, in essence, doing IFR-type navigation. You are totally dependent upon your navigation gear. For that reason, the instant you get established on course above the cloud tops, decide on a good compass heading that will hold your course line - not a DG heading or anything else that relies on a functioning electrical or vacuum system. Prepare for the impossible and have the compass heading as a backup just in case everything else decides to quit. It's also necessary to re-establish a compass heading when you get on top because it is quite common for the winds on top of a deck to be significantly different than those beneath it. That means a compass heading that worked down low may not be right up above the clouds. All of this amounts to just one more reason to make sure you have plenty of fuel, just in case the winds on your nose pick up. Also, take a time hack at your last confirmed location and write it down along with an estimate of what time you should arrive over your destination. This is all basic cross-country planning, but it becomes especially important when you can't see the ground easily.

Again, and I'll harp on this constantly, monitor the condition of the clouds under you, and if it looks as if the holes are disappearing, be conservative and drop back down. Don't chance getting stuck on top. Also, top the clouds by at least 2,000 feet for a number of reasons. First, you want as much altitude as you can so you can see further ahead and see what the holes are doing. Also, it's no fun to have a fast moving jet climb through the clouds under you and ruin your day.

The traffic thing brings up another point: You may be VFR, but in the world of clouds a lot of folks are IFR, and you have to remember they are there and they may not be expecting you. That's part of the reason for the 2,000-foot horizontal separation requirement for VFR operations - and it still isn't really enough. If you're descending through a hole in the clouds and someone flying on the gauges pops into your little hole as you go through his flight level, he's not going to be looking for you because he'll be head down looking at the instruments. So spend as little time as possible in the hole and keep your eyes open. Also, when you drop out of the bottom of the clouds, quickly visually clear the area around you so you don't surprise some poor soul who is waddling along 500 feet under the deck.

The real cure for all of this is simple: Get an instrument ticket and keep it current. The biggest use for an instrument ticket isn't so that you can file when everything is klagged-in. The best use of the rating for the casual IFR pilot is the ability to file and legally fly up through a relatively thin deck to VFR on top and then not have to worry too much about what's happening to the holes at the destination. If you set yourself some healthy minimums - say 1,500 feet of clearance beneath the clouds - you may never have to fly an IFR approach, but you'll use that ticket a lot just going up and down through decks. Of course, you'll still want to make sure you aren't flying into convective weather.

VFR over the top works, and it should be used. But it should be approached with a great deal of planning and an understanding of what can go wrong if you push it to the limit. Always err on the safe side and, when the holes start disappearing, get yourself down under those clouds, pronto.


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