Weather Margins Act as Tool to Manage Uncertainty for Pilots

I am still a student of weather even though I have been a meteorologist for nearly 45 years and a flight instructor for the past 25. Although it’s not something I’ve ever truly mastered, weather is a force of nature that I deeply respect. In fact, when there’s an aviation accident that may have been related to weather, that gets my attention and sparks my curiosity. I consider it an opportunity or invitation to learn, not only for my own benefit but for that of my students and anyone else willing to listen. 

Even before the National Transportation Safety Board (NTSB) makes its preliminary report a week or two after such an accident, I put on my weather forensics hat to see if I can begin to tell the story. Although every accident has its own unique characters and plot, for many the storyline often comes down to something as simple as the PIC not protecting the margins. Let’s dive in and see what it means to protect the margins as it relates to weather.

You may have heard the term “margin of error,” especially as it concerns polls and other statistical data. The term margin of error isn’t used in the aviation industry, especially as it relates to weather. It’s defined in the Oxford dictionary as a “ permissible or tolerable degree of deviation from a correct or exact value or target.” “Your landing was well within the margin of error” is not something that you hear from your flight instructor. We generally don’t think in those terms. 

Nevertheless, margins are indeed woven throughout the fabric of every flight you take. There are fuel reserve margins, climb performance margins, takeoff distance margins, landing distance margins, weight and balance margins, etc. There’s no doubt that we always need to protect those margins. Failure to do so may lead to an accident or, at the very least, a heart-pounding incident. In fact, failing to protect these margins that ultimately lead to an accident, fatal or otherwise, is one that is very preventable.    

The FAA mandates that we stay within those margins. If we decide to test those margins on any given flight, we become the proverbial test pilot. Weather, on the other hand, is just too unpredictable and complex to be discussed as a margin of error. It’s really better described as a margin of uncertainty. Other than some regulations that do not permit flight in certain weather conditions (e.g., flight into known icing conditions, or FIKI), we have no defined margins with respect to weather. It is left solely up to the pilot to define and protect those margins whatever they may be. To accomplish this means learning how to quantify risk.  

Since I earned my flight instructor’s certificate, I have examined dozens if not hundreds of aviation accidents. Sifting through all of the weather guidance that was available to the pilot often creates more questions than answers, even after the NTSB final report is released. Did the pilot get a weather briefing shortly before departing? If so, what weather guidance did they rely on? Did they understand the briefing? Did they miss something critical? Was the forecast accurate? Introspectively, would I have seen this coming from the weather guidance that was present? It is the answer to this last question that always keeps me scratching my head.   

“Airmanship begins before you leave the ground” is a quote from the Student Pilot Handbook written by Jack Hunt and Ray Fahringer. Published in 1943, the words still hold true today. It’s a succinct statement that carries a ton of weight. If you peel the onion, however, airmanship is less about how you manage aircraft systems as you might have been taught and more about quantifying and managing any uncertainty that exists. 

Margins give us the tool to manage any uncertainty even before we taxi to depart. They should never become background noise and should always be front and center. We can’t just shrug it off and rely on hope as our plan. Every decision we make before or during flight needs to have those margins in mind. Of course, that requires that we have a game plan or strategy in place, which takes time and commitment. 

When we’re doing our job as PIC, we usually are thinking one or two steps ahead. We continuously weigh the risks and manage the uncertainty ahead of time. This is a skill that is typically acquired as we gain flight experience and isn’t usually something we are taught during primary training. In fact, for most of us, we are actually doing all of this and just don’t know it. The key factor is that we don’t want to be reactionary and must be working from a plan.  

For example, if we know we’re facing a landing with gusty winds, we should have a strategy in place long before we enter into the airport’s terminal area. As we approach the airport, our plan is to gather information by listening to the weather report from the ground-to-air frequency or fly over the airport and examine the wind sock. We can quantify the risk at this point and have a plan to mitigate that risk long before we are on short final. One approach we are taught is to keep our speed up when faced with gusty winds. Perhaps you’ve heard a rule of thumb to add half the gust factor to your final approach speed as part of a strategy for dealing with gusty surface winds. 

As we enter the pattern, we extend our flaps accordingly, manage our speed, and monitor the approach—always being ready to go around when we are no longer within our margins. That may lead us to find a different airport that may eat into our fuel reserves. Of course, we planned for that potential before we departed, right? This is just one example of how we faithfully protect the margins.  In this gusty wind scenario, would our risk be the same if the runway was 40 feet wide versus 150 feet? The margins are quite a bit different with a narrow-versus-wide runway. The narrow runway creates more uncertainty, and that may mean adjusting your margins to be way more conservative. Of course, it could be that your home airport has that narrow runway, and your experience landing in gusty winds at this airport may also decrease the uncertainty.

As it relates to weather, we are quantifying probabilistic risk. This is much different than specific risks that are regulatory, such as determining the weight and balance before takeoff. Consequently, there are no tables in our POH that we can use to define these margins. So, the FAA does not go out of its way to define this for us. Therefore, it may seem as if this is completely optional. While the regulations do state if you are making a cross-country flight that you need to examine the weather reports and forecasts prior to flight. In the end, it is our responsibility to list any element of weather that adds risk to the flight and quantify it before departure and during the flight.

Personal weather minimums are the tool we use to quantify and manage this probabilistic risk. This begins with identifying the key weather elements that add risk to the flight. This includes turbulence, airframe icing, ceilings and visibility, convective potential, and surface winds, just to name a few. When determining weight and balance, the calculation is quite easy. You are either within the envelope or you are not. Basically, it’s black and white. That’s not the case for weather. Due to the probabilistic nature of weather, it’s never about being black and white and more about shades of gray. Therefore, the overarching goal is to minimize your exposure to adverse weather and personal minimums are the key to perfecting a strategic plan. 

One approach is to draw a hard line in the sand for each weather element. For example, you could define the maximum crosswind component personal minimum as, say, 18 knots. That is, if the crosswind is forecast to be stronger than 18 knots at the time of arrival at your destination, this equates to a flight with high risk. But to deal with the uncertainty in such a forecast, it would be better to create a conservative personal minimum that is your no-brainer crosswind number, meaning that any crosswind that is expected to be, say, 12 knots or less will give you plenty of margin to deal with that uncertainty and therefore becomes a flight with low risk. 

Therefore, any expected crosswind between 12 and 18 knots at your destination creates a moderate risk. When operating in the moderate risk area, you should always have a secondary plan or strategy to deal with that situation if it turns out the actual crosswind is greater than 18 knots upon arrival. Your plan is to find an alternate airport where crosswinds are expected within your conservative personal minimum, or 12 knots in this example. You have a solid strategy at this point, and you are actively protecting the margins.  

So, essentially, you are always defining two personal minimums for each weather element that adds risk to the flight. There’s one that represents your actual personal minimum and another that is your conservative personal minimum. You should strive to always be planning flights on the conservative side to account for the uncertainty or those shades of gray. 

In fact, in my EZWxBrief progressive web app, I like to color code these using a traffic light concept. That is, red is high risk, green low risk, and yellow  moderate risk. Pilots love to see green, so it’s a bit of a psychological element to allow you to stack the deck in your favor, namely, lean toward green. This is not to say you can’t plan a safe flight when this evaluation is yellow or even red, but you really are at the edge of the margins when doing so.    

Ceiling and visibility also add risk to the flight. These need to be quantified along your proposed route as well as at your departure and destination airport using the available weather reports and forecasts. Of course, this will largely depend on whether you are making the flight VFR or IFR. If you are flying IFR, ceiling and visibility are actually one of the few weather elements that are baked into the IFR planning system. That is, you must use the 1-2-3 rule that states one hour before to one hour after your ETA (at the listed destination) the ceiling will be at least 2,000 feet, and the visibility will be at least 3 sm. If not, you will need to file an alternate airport. This somewhat smells a lot like that conservative personal minimum for both ceiling and visibility. Of course, your own personal minimums will likely be different.  

Making a flight under IFR may allow you to have lower personal minimums, but you still need to plan for this uncertainty. Your personal minimum for ceiling at your departure airport may be 700 feet. Your conservative personal minimum may be 1,500 feet. If the ceiling forecast or weather report at your departure time is 2,000 feet, you are golden and have plenty of margin. However, if the ceiling is 1,000 feet, you are operating in the moderate risk area and may need to adjust your time of departure that gives you the green light and widens the margin. Again, this doesn’t mean you can’t depart, but you better have a plan to deal with rapidly changing and worsening conditions not anticipated. 

The plan or strategy needs to be fluid. At some point in your survey of all available weather guidance, you will stop your analysis and depart. By any stretch of the imagination, you are never done with respect to weather. It’s not about checking the box like you might with your weight and balance calculation. In fact, there’s always more to examine even after you depart. Last but not least, you will always have the student mindset—there’s always more to learn about the complex topic of weather.

This feature first appeared in the January Issue 954 of the FLYING print edition.