Weather Matters

 

 

I got a request the other day from someone who wanted to use one of my articles in his online aviation course on computer flight planning. His business is called www.PilotWeatherTraining.com,  and I checked it out and it got me thinking about weather.  I haven’t tackled aviation weather since I was writing full time back in the mid 80’s, and with another 10,000 hours of so of experience since then,  I thought it might be time to think about it again. Specifically, what kind of weather matters, and what doesn’t?

First, what do we mean by the word “weather”? Weather is atmospheric conditions. A severe clear day with no wind is still weather.  But in aviation, when we talk about “weather”, we mean the stuff that can adversely affect our flight.  If the skies were never any worse than scattered clouds, visibility greater than 10 miles and winds under 10 miles per hour, we really wouldn’t ever need to worry much about the weather—it’s always a “go”. But that’s not the case, not even in the relatively dry southwestern states (US), so weather is something we have to take into account.

For the VFR only pilot, “weather” is not so much a question of avoiding the stuff that can really hurt you as it is having adequate visibility to navigate and avoid terrain and obstacles.  Of course the VFR pilot wants to avoid freezing rain and thunderstorms and heavy turbulence, but that should largely take care of itself if he or she has adequate visibility in the first place. So what is “adequate”? “It depends” is always a safe answer but doesn’t get us very far.  The normal VFR visibility minimums of 3 miles might be adequate, or it might not be.  The VFR only pilot flying a Champ at 80 mph on a very hazy summer day on a very short trip over terrain he or she is totally familiar with can probably call 3 miles visibility adequate.  Another pilot flying a Piper Arrow or a Cessna 182 on a longer trip over unfamiliar terrain would be asking for trouble in those conditions.  So visibility depends a lot on speed and familiarity with the terrain.

What about clouds? VFR minimums say you must be at least 500 feet under any clouds, 2000 feet away from any clouds, and at least 1000 above any cloud.  It’s okay to fly between them and it’s okay to fly over them as long as you stay that far away from them.  (This is to provide some reaction time in case an aircraft, one presumably operating under Instrument Flight Rules, comes popping out of one of those clouds.) So I guess that means that as long as we are willing to stay under the clouds, we could fly even with overcast skies.  And for short trips that probably is okay.  The problem with overcast skies is that the ceiling almost always gets lower as you approach the system that is causing the overcast.  If you are flying away from that system, toward higher ceilings and eventually broken, then scattered clouds, fine.  Otherwise, you better not be going far because you’re going to find yourself having to go lower and lower to stay under the overcast, and down that road lies trouble.

The real problem with VFR only flying is its intended purpose: If you intend to fly VFR for transportation you are going to run into problems; if you intend to fly VFR for pleasure, you are probably going to have a ball.  (See numerous previous posts on “Oshkosh”—Air Adventure—to get an idea of how much fun flying for fun can be.)  And the reason is quite simple, even if it is still quite hard to accept: flying for transportation, that  is, flying at a given time to a specific place over a given distance and course, requires tools to deal with the realities of weather, and VFR only flying doesn’t have those tools.

The only way to consistently and reliably fly for transportation is under Instrument Flight Rules with an appropriately equipped aircraft and by a suitably qualified and current instrument rated pilot.  That takes care of the visibility limitations of VFR only flying, and it takes the risk out of flying on top of broken clouds or overcast skies, but now the problem of avoiding hazardous weather doesn’t take care of itself.  So what are those hazards, and what can we do to avoid them?

I like to think of hazardous weather as any weather I don’t ever want to encounter in any aircraft.  The L-1011 was a fabulous aircraft, I think the best air transport ever made. (Certainly newer aircraft have better systems and are more efficient, but manufacturers have discovered that aircraft don’t have to be the best that can be made, just good enough.)  As good as it was, I still wouldn’t want to take it into thunderstorms, or  severe turbulence, nor would I want to take it through heavy icing, hail, or freezing rain on takeoff, approach or landing. There are limits to the stresses any aircraft can take, and there are limits to the amount of ice it can carry and damage it can sustain. General aviation aircraft are normally certified to greater G limits than transport category aircraft, but I still wouldn’t want to take any aircraft into a thunderstorm or heavy turbulence.  (That includes an F-16 stressed to plus 10 G’s, not that I’m going to get a chance to try.)

The L-1011 had every kind of anti-icing equipment imaginable, of course, and it also had something else—it could climb rapidly through the lower altitudes where serious icing is normally found up to the flight levels where the temps are so cold that icing is seldom found. Anti icing for turbofan aircraft is mostly  a matter of keeping the engine cowling clear and the pitot/static system heated.  General aviation aircraft are different, not just because they spend a lot of time at altitudes where icing occurs, but because it affects them differently.  It is fairly easy to protect a propeller driven, reciprocating engine from ice: you need “hot “ props and an alternate air source. But keeping the aerodynamic surfaces clean—the wing, the tail, the rudder—that is a different matter.  In some 12000 hours of flying jets, I can count on one hand the number of times I had to use wing deicing.  In some 2000 hours flying general aviation aircraft, I can’t count the number of times I had to use wing deice—“the boots”—and I do remember many times when they didn’t work very well. Approval for flight in known icing is great, but only to get you out of it if you happen to fly into it.  General aviation aircraft should avoid any icing conditions and, if encountered anyway, get out of them as soon as they can. 

The L-1011 also had an incredible radar, with a bunch of power and a great big antenna up in the nose, and I learned from experience to trust it and  to rely on it: If it showed a red area inside a cloud, you could bet your 401(k) that that cloud was a thunderstorm.  If it showed mostly green areas of precip with a few smaller areas of yellow (heavier rain), you could feel safe entering, avoiding the yellow areas. Radar in general aviation aircraft aren't nearly as powerful or as sensitive and can’t be relied on for weather penetration.  They should be used to avoid areas that might contain thunderstorms.  The same goes for ground based weather radar relayed to cockpit displays.  They paint a good picture, better than most aircraft radar pictures, but they are refreshed much less often than aircraft radar, so they aren’t real time.  The two should be used to together, if you have both, to stay completely away from any weather that might contain thunderstorms. Remember, you don’t ever want to fly in a thunderstorm in any aircraft. One time is one too many.

One final note on avoiding thunderstorms from an “old guy” who has been there a lot: the best way to avoid thunderstorms is to flight plan away from them. I don’t care how far out of the way you have to fly, do whatever you have to do to avoid any chance of having to deal with them.  And I don’t care if it means you probably shouldn’t fly at all that day. No airplane can fly anytime under any conditions.  The less weather capability you have, the more often you will come upon those days, and the further out of the way you will have to fly on days you can, but so what? There is no trip so important that taking a chance on hazardous weather justifies it.  And please don’t be tempted to try a “look-see” under VFR.  That leads to nothing but trouble, like when you turn around and the weather has closed in behind you as well.  Just stay away from thunderstorms.

You want to stay completely away from freezing rain and hail in flight, but they are not the same kind of hazard.  Hail comes out of thunderstorms, and you shouldn’t be anywhere near them.  We went over that.  Freezing rain happens when rain falls into colder, freezing temperatures.  At the first hint of freezing rain, climb if you can.  You usually only have to go up a couple of thousand feet to climb into warmer air with rain.  If you can’t do that, turn around. Going lower almost never works, and trying it exposes you that much longer to what can quickly coat the aircraft and add hundreds of pounds of additional weight.  It isn’t worth the gamble.  Go back.

That leaves turbulence not associated with thunderstorms, and it really doesn’t matter what kind of turbulence it is—mountain wave, convective, jet steam, clear air—if the forecast or reported turbulence is severe or extreme, don’t go there.  If it is moderate, you may not want to go there—the ride will be awful and aircraft control will be a tiring, constant battle, but it won’t hurt you.  Unless it gets worse.  Turbulence of any sort is best avoided, but it’s the severe stuff that will hurt you. Again, the best way to avoid turbulence is in the preflight planning, and the only way to find out about it is with a complete weather briefing.

Actually, I tried to summarize all of these elements of safe cross country flying back when I was writing full time, first in my book Fly Like a Pro and later in Improve Your Flying Skills. The result was a mnemonic (like GUMP, for the prelanding check).  My mnemonic for preflight planning was BILAHs, pronounced “bylaws”.  That may have been a long time ago, but the basics never change. Here’s how it works:

• The B is for briefing, meaning weather briefing.  Always get a complete weather briefing for every flight outside the local area.

·         The I is for IFR.  Always file IFR, if you can, and if you can’t, either accept that your flying is going to be mostly local, or start working on it.  The reason to file IFR every time is that that is the only way to stay current and be comfortable with the ATC system.  If you aren’t comfortable filing IFR on a good day, how comfortable are you going to feel on a lousy day when you have to?

 

·         The F is for flight log.  Always make a flight log with legs, times, fuel estimates and keep it current enroute.  It is the only way to see trouble coming.
 

·         The A is for alternate: always have one, required or not, and make it a good one.  A solid gold alternate with the fuel to get there is the best “out” in aviation. (See January 2010 post, “The Other Part of Flight Planning” for more on this.)
 

·         The H is for hazardous weather.  Stay away from it.  That’s what this post is all about.
 

If you follow these simple BILAHs of cross country flying, you will eliminate 90% of the problems general aviation pilots get into. Commercial pilots don’t have any choice, they have to fly this way.  You have a choice, but do it anyway.  It’s a little more work, but in the long run it’s a lot more fun and sure beats scaring yourself to death.