Tailwind Takeoffs and Landings
1. Take off and land into the wind
Common sense says to always perform takeoffs and landings into the wind. Doing so, the plane will require a shorter ground run before becoming airborne, and it will land with a lower ground speed and a shorter distance traveled before coming to a stop. It will climb out at a steeper angle, and during the approach to landing, it will descend at a steeper angle as well.
However, it is not always possible to follow this simple advice. UL (ultralight) pilots often fly out of strips with obstructions such as trees or powerlines at one end that make a takeoff possible in only one direction. That is, the strip is “one way out, and one way back in.” If the wind is blowing the wrong way, it is take off downwind or do not fly. The presumption is that the runway is not unduly long.
It is likely that UL pilots encounter this situation far more frequently than GA (general aviation) pilots who almost always fly in and out of “real airports” with paved runways and a gas truck. The traditional wisdom for GA pilots is “Never take off downwind. Just don't do it.” This may explain why there's so little information available on “tailwind takeoffs” and what you can expect when you attempt one.
The following sections describe some of the things you should take into account when considering a takoff or landing when the wind is not favorable. Many variables come into play and in varying degrees.
2. Airspeed, wind speed, and ground speed
Airspeed is simply the speed of the air moving past the plane, or from a different point of view, it is the speed with which the plane moves through the air. In the cockpit, the pilot reads the airspeed from the airspeed indicator.
Ground speed is the speed of the plane relative to the ground. When there is no wind, the ground speed will be the same as the airspeed. But when the wind is blowing, airspeed and ground speed will not be the same.
Suppose a plane is flying at 60 mph just above the runway, with no wind. In no-wind conditions, the airspeed and ground speed will be the same, 60 mph in this case.
Now assume the wind is blowing straight down the runway at 10 mph. With the plane still flying at an airspeed of 60 mph and into the wind, its ground speed will be only 50 mph. But going in the other direction, flying with the wind, the ground speed will be 70 mph. Ground speed is less than airspeed when flying into the wind.
To illustrate the effect of this, suppose the runway is exactly one mile long. How long will it take the plane to go from one end to the other while maintaining an airspeed of 60 mph at all times?
If there is no wind, the plane will take 60 seconds to fly the length of the runway. Flying in the direction that produces a headwind, 72 seconds will be required. In the other direction, with a headwind, 51.4 seconds. Note that the difference between the headwind and tailwind situations is more than 20 seconds!
Here's a tidbit that illustrates the relationship between airspeed, wind speed, and ground speed. A Canadian pilot frequently flies his Challenger when the winds aloft are upwards of 40 mph. Now, by setting the throttle just right, a Challenger will easily fly straight and level at 40 mph. So this pilot delights in pointing his plane into the wind and “hovering” over the field, to the amazement of the spectators below.
What's the airspeed of the hovering Challenger? 40 mph. What's the wind speed? 40 mph. What's the ground speed? Zero. The plane just hangs up there!
3. A Plane is a Dandelion Seed
An obvious point is that there is no frictional contact between a plane and the ground once the plane is in the air. The plane will move freely when the slightest force is exerted on it. Only air resistance retards the motion.
So, it doesn't take long after takeoff for the wind to blow against the plane and start it moving in the direction the wind is blowing. After a short time, the plane will be floating with the wind just as if it were a dandelion seed, a bit of fluff drifting with the wind.
The forward speed of the plane will be much more evident than the motion of the plane due to the wind. But the motion of the plane with the wind is still there and it forms a component of the planes motion relative to the ground.
You can see this drifting with the wind during the approach to the runway in a crosswind. If you point the nose of the plane straight toward the end of the runway, the plane will be observed to drift to the side. To go straight toward the runway, you must turn the plane a few degrees into the wind (crab) to compensate for the sideways drift.
Even better, fly the plane straight down the center of the runway while there is a good crosswind blowing. You will note that the plane actually travels down the runway sort of sideways. If you point the nose of the plane straight down the runway, the wind drift will carry you off to the side.
4. Aircraft Performance and Wind Speed
Because an airplane drifts with the wind, it doesn't feel the wind. Only a brief time is required for its drift velocity to come up to match the speed of the wind . This is true for planes of all sizes, UL's and airliners alike.
The previous statement assumes a smooth, steady wind. If the wind is gusty, the plane will indeed feel impacts from the gusts because the duration of a gust is too brief for the plane to develop the drift to match.
All the performance parameters of the plane will be the same while flying in wind as when flying in perfect calm. The rate of climb will be the same and the stall will occur at the same airspeed. The airspeed for best rate of climb will be the same, and the airspeed for the best glide will be the same.
So if the plane doesn't even feel the wind, why is the wind so important to takeoffs and landings? Answer: Ground speed. The wind has a direct effect upon ground speed, and it is the ground speed that causes the runway to get behind you quickly.
5. Surface Winds vs. Winds Aloft
When an air mass moves across the ground, the bottom part of it tends to be slowed by objects on the ground. For this reason, surface winds are typically not as strong as the winds aloft.
This has two implications for the pilot. First, expect the wind speed to be greater a short distance above the ground than what you observe on the ground. This effect is likely to be more pronounced if the runway is immediately adjacent to a wooded area.
Second, there will be a shear layer between the layers of slow-moving and fast-moving air. Some turbulence may be encountered while flying in this layer, but it usually is not strong enough to cause any real problems. The greater hazard is to let the sudden bumpiness distract you so that you do not pay proper attention to other matters, like airspeed, for example.
6. Taking Off with a Tailwind vs. a Headwind
The bottom line is that more runway will be required along with a greater distance to climb over an obstruction at the end of the runway.
Suppose a plane requires a ground run of 200 feet to lift off at 40 mph. It climbs out at 500 ft/min at an airspeed of 45 mph. It's operating off a runway that is 1,000 ft long.
After making a few assumptions, we can use some basic physics to get at least an idea of the effect of the wind. The big assumption is that the acceleration of the plane is constant during its takeoff run. This is almost certainly not the case, but hopefully the resulting error is not great.
So, realizing the possibility for inaccuracy, here are the results:
Note that a 10 mph tailwind almost doubles the takeoff roll, 384 ft as opposed to 200 ft. The sensation felt by the pilot in such a case is that the plane doesn't want to come off the ground! And after it does, it doesn't want to climb like it normally does.
Clearing obstructions at end of runway
Observe in the tabulation above that the altitude gained by the time the plane crosses the end of the runway decreases significantly with a tailwind. With a 15 mph tailwind, it is about half the no-wind value.
There is another factor to consider. Recall the earlier discussion about how the wind a short distance above the surface is likely to be stronger than the wind at the surface. As the plane climbs upward from the runway, it will likely be entering the region where the tailwind is stronger. This has two effects.
(1) As the plane penetrates the layer where the tailwind speed is greater, the airspeed will drop, momentarily, until the “drift with the wind” phenomenon has time to develop. And because lift is dependent upon airspeed, the rate of climb of the plane will decrease. (2) At the same time, a bit of bumpiness or turbulence may be felt as the plane passes through the shear layer between the slower and faster layers of air.
Here's the picture seen by the pilot: After a much longer than usual ground run, the plane seems to gain altitude at a much shallower angle. It's moving fast down the runway, but it doesn't want to climb. Then there is a bit of turbulence, and the plane begins to feel mushy with a tendency to wallow around. A glance at the airspeed indicator shows it to be lower than what it was just a second ago! And the trees are getting closer all the while.
Now let's assume the pilot clears the trees and continues the climb. In just 10 seconds or so, the plane will have begun to move with the wind. From that point on, the rate of climb of the plane will be its normal value, but the angle of climb will be less because of the increased ground speed. It's only at this point that the pilot can begin to relax a bit.
If the runway has a significant slope or grade, the preference is to take off going down hill but land going up hill. The plane will accelerate more rapidly going down hill, and it will slow down quicker going uphill. There is no mystery in this.
When the wind blows, even this has to be reconsidered. Sometimes it is better to take off uphill into a strong headwind than it is to go downhill with an equally strong tailwind. The worst case is to attempt a takeoff uphill with a tailwind. In that situation, everything is working against you.
The direction to choose for the takeoff attempt (assuming you have a choice) depends upon the degree of the slope and the strength of the wind. It's a judgement call to be made by the pilot.
7. Tailwind Landings
The bottom line is that you will arrive at the touchdown point going much faster than usual. The hazard lies in over-running the runway and colliding with objects or hostile terrain off the end.
When flying with a tailwind, the ground speed will be the sum of the airspeed and wind speed.. The speed of the plane at touchdown will be higher than the calm-air touchdown speed an amount equal to the speed of the wind. Consequently, more distance will be required to come to a stop.
Also, assuming that the plane descends at its normal rate in feet/minute, the angle of descent will be shallower because of its increased ground speed.
If the approach to the runway is free of obstructions, the pilot may make a lower than usual approach so that the plane has minimal energy associated with height. This leaves only the energy of the increased speed to be dissipated. The flat approach will also give more time for the plane to react to changes in wind speed as it descends through any shear layer that may be present.
Here is the Big Hazard: The pilot must keep a sharp eye on the airspeed indicator and be ready to add power if it even gives a hint that it's going to decrease. And especially, the pilot must not judge his speed by looking out the window at objects on the ground. In this situation, it is airspeed, airspeed, airspeed!
The reason for this is that objects on the ground will appear to be zipping by at a speed much higher than in a normal, non-tailwind landing. If the pilot reacts to the high ground speed and slows the plane down until “it looks right,” the airspeed will then be too low by an amount equal to the wind speed. This can easily lead to an unexpected stall or at least a high sink rate that will come on quite suddenly.
Tailwind landing over an obstacle
If a landing over an obstacle must be made in tailwind conditions, it is desirable to cross the obstacle at the lowest altitude and lowest airspeed possible, consistent with safe operation of the plane. The intent of this is to arrive at the touchdown point with a minimum of excess speed. That is, cross the obstacle as low and as slow as you can, but not too low, and not too slow, for the sake of safety.
Suppose the approach to the runway is over a wooded area so that you normally clear the trees and then descend rather steeply to the level of the runway. With a tailwind, at least two additional factors must be considered.
Windy conditions will usually produce turbulence a short distance above the trees. Turbulence gives a bumpy ride with bumps upward and bumps downward. It's the downward bumps that you must watch out for and guard against. Therefore, in windy, turbulent conditions, an extra margin of distance between the trees and the path of the plane is appropriate. It's tempting to say that you should also carry a little extra airspeed, but this adds to the high ground speed problem of the tailwind landing. It's a Catch 22
Secondly, once we make it over the trees and initiate the decent to the runway, we can expect the tailwinds to suddenly diminish significantly as the plane approaches the runway. This will cause our airspeed to shoot upward. Why?
While flying above the trees in the tailwind, the ground speed will be higher than the airspeed by an amount equal to the speed of the wind. Now, when the tailwind suddenly disappears, the airspeed becomes equal to the ground speed. That is, it will increase.
The end result is that we arrive at the runway with excess airspeed. The plane will float farther in the flair before touching down, just as it does on a landing in calm air when our approach is a bit fast.
All the effects described above are subject to local conditions and may be rather pronounced, just discernable, or they may not occur at all. Such is the nature of flying. However, the pilot should be aware of the possibilities and be prepared to take them in stride when they do occur.
8. Landing into a Headwind over an Obstacle
Headwinds are much preferred over tailwinds, but here's a way to get into trouble while landing into a headwind. As in the previous section, suppose the approach is to a runway that is surrounded by trees and woods.
We make the approach rather routinely, but note that the angle of decent is much steeper than what we usually observe in calm conditions. No problem. We just tweak in a bit more power so that we descend at a shallower angle. We clear the trees and start the descent to the runway. Here's where the surprise comes in!
Because the runway is surrounded by woods and trees, it is largely sheltered from the winds blowing above. While above the trees, we have a headwind and the lower ground speed that comes with a headwind. But when we drop below the level of the trees, the headwind suddenly disappears!
What are we left with? Only the ground speed we had up high in the wind, and this will be less than the airspeed we had above the trees. That is, the airspeed will drop as we descend toward the runway into the calm air.
The result can range from inconsequential to rather exciting. If we were carrying a bit of extra airspeed on the approach, the sudden loss of airspeed will likely have no undesirable effect. But, if we were near the bottom limit, the sudden decrease could possibly put us into a situation where a high sink rate develops. Unless corrected by the addition of power, and quickly, a hard and potentially damaging landing may follow.
9. Complicating Factors relating to Tailwind Takeoffs
As often as not, when we are faced with a takeoff with a tailwind, other factors come into play that complicate the situation. Typically, when a pilot gets into trouble, it is a combination of several things rather than one single item that proves to be the cause of the difficulty. Here are some things to consider:
A takeoff going downhill is preferred. An uphill grade will lengthen the takeoff run.
If the strip is soft and spongy from recent rains or melting snow, you can expect the takeoff roll to be lengthened considerably. Tall grass on the field will have a similar effect. A soft field with tall grass is even worse.
For many aircraft it is recommended that a takeoff run from a soft field be done with a considerable nose-high attitude compared to a normal takeoff. This is to get the weight off the wheels and onto the wings as soon as possible. However, once the plane becomes airborne, you must lower the nose immediately in order to “get back to normal” as soon as possible.
The trick is to lower the nose and gain speed without letting the plane sink back onto the runway. And, you don't want to lug it into the air only to have it stall immediately. However, the plane will usually accelerate quickly once the wheels come off the ground.
You can simulate a soft-field takeoff for practice in normal conditions by reducing engine power appropriately. This is best done under the watchful eye of an instructor or a more-experienced pilot. Add power once the wheels leave the ground to simulate the “breakaway.”
For some reason, grass that is wet, whether from rain or dew, proves to be much “stickier” than dry grass. Expect a longer takeoff run if the grass is wet. Lifting the nose wheel early will be beneficial but it is unlikely that the extreme nose-high attitude of the soft field takeoff will help very much (unless the field is soft as well).
Wet grass also has a negative effect on a high-speed landing, It will slow you quickly at touchdown, but then when you hit the brakes, the braking action is much reduced because the wheels tend to slip and skid over the slick grass.
If the wind is gusty, or if its direction is not constant, expect the takeoff to be a lot more exciting than if the wind is strong but smooth and steady.
On a hard surface (pavement or hard dirt), low tire pressure will add considerable distance to the takeoff run because of the flexing of the tires.
On a soft surface, the effect of low tire pressure will be less noticable. But remember, the takeoff run is going to be considerably longer than if you were on pavement even with the tires properly inflated. There is a tradeoff involved here. High tire pressure produces a smaller footprint which may cause the tire to “sink in” more than a tire with lower pressure and a larger footprint.
Tailwind with crosswind component
If the wind is blowing from a direction other than from straight behind the plane, the plane will have a tendency to drift sideways once it has lifted off. You will have to set up a crab quickly to compensate for this drift and do it while contending with the shallow angle of climb and high ground speed produced by the tailwind. This can make for a busy ride.
The Bottom Line: Be alert to all the factors that can affect a takeoff. Don't become so focused on the tailwind and the trees at the end of the runway that you fail to notice the tall, wet grass and the underinflated tires. Things can add up to ruin your day.
10. The Go-No-Go Decision
You, the pilot, must make the decision whether to attempt a takeoff in adverse conditions. No one can make it for you. Here are some points to consider:
You should be familiar with the performance capabilities of your plane. What is the typical takeoff run? How steeply can it climb? What's the shortest stopping distance from takeoff speed? And so forth.
How heavily will the plane be loaded for this flight? A heavy plane will require a longer takeoff run and will climb more slowly.
Do you know exactly how fast the wind is blowing? How accurately can you judge wind speed? There is a lot of difference between taking off in a 10 mph wind vs. taking off in a 15 mph wind.
Are your piloting skills up to the task? Let's face it. Some airplane drivers are better than others, and some can handle adverse conditions better than others. Have you flown recently? Have you flown in comparable conditions before?
Are you being pressured into an uncomfortable situation by other pilots, an eager passenger, or spectators? If you feel obligated to make the attempt, that's not a good sign.
Have you considered all the variables? Wind? Weight? Soft field? Wet grass? Tires properly inflated?
Once you've made the decision to go, you may still feel a bit of apprehension. That's OK. A bit of apprehension seems to sharpen the mind. But if you're honestly nervous or just plain scared to the point that you can't concentrate, or you become fumble-fingered and start forgetting to do or check familiar items ... Stop and get out. You don't really have to do it. Discretion is the better part of valor.
Remember, once you're up there, you must come down again. While you're evaluating the possibilities for a takeoff, also be thinking about the possibilities for a landing. It's embarrassing to have to have someone come up and get you, or reel up a rope ladder so you can climb down.
Finally, “When in doubt, get out.” Get out of the plane, that is. Maybe tomorrow will be a better day, and by getting out, you may just be saving the plane so it will be available to fly tomorrow!
11. Working Your Way Out of a Tight Spot
Sometimes things don't go as planned or we fail to plan for the way things go. We find ourselves in a tight spot, in a bit of a situation, if you please. Here are a few examples with some suggestions that may save the day.
When to abort a takeoff
With experience in a particular plane, a pilot develops a feel for the plane, becomes aware of its response to the controls, and most importantly, develops a sense of how quickly it accelerates and gains speed in a normal takeoff. Having this knowledge of the sound and feel of the plane, the pilot should then be always on the alert for anything unusual. A different sound, a vibration not noticed before, or a sluggish acceleration could prove to be a vital clue that all is not well.
As to when to abort a takeoff, the sooner the better, before a lot of speed has developed and while a considerable fraction of the runway is still in front of you. It's not a big deal to reduce power, slow down, turn around, and taxi back to the starting point, taking stock of the situation as you do.
Watch how fast your speed increases during the takeoff run. If the speed comes up to just below takeoff speed and then seems to hang there, it is likely you will have to abort. The speed should increase steadily, but it is likely that the rate of increase will be less as your speed increases. And keep in mind that you will travel a lot farther while the speed increases from 35 to 40 than you did while the speed increased from 30 to 35, for example.
Glance down the runway and visualize what should be happening at various points. Where is the point farthest down the runway that you can reduce power and stop uneventfully? Is there a point where, when you pass it, you are committed to the takeoff with no possibility for an uneventful abort? Runway situations are different; you must evaluate the possibilities at your own strip.
If you do not abort, what are the implications of a failed takeoff attempt? This can range from merely running off the end of the runway and bouncing along across a hayfield, to going through a fence or plunging into a ditch, or to crashing into trees. That is, the consequences range from negligible to catastrophic. Take this into account as you make your go-no-go decision.
When to abort a landing attempt and go around
Just as for the takeoff, the sooner the better. A good landing begins with a good approach. If the approach is bad, it is not likely the landing will be much better. You will either be high or low, fast or slow, or not aligned with the runway. And if you decide to go around early, you don't really have to admit to starting the approach in the first place. You just decided to fly around a little more.
If the runway is free from obstructions at both ends, it may be possible to abort a landing attempt at any point, right down to or even after touchdown. In fact, one way to recover from a bad bounce is to throw the power to it and go around for another try. But, in many cases, the presence of obstructions make a go around from touchdown or short final impossible.
Once you decide to go around, be decisive about it. Don't apply a burst of power and then second guess the decision. You can wind up too high and too fast by doing this. Better to do an unnecessary go-around than to commit to a landing and then wish you had gone around for another try.
Locate the point where, after you pass it, you are committed to land. Obviously, the decision to abort the landing attempt must be made before you reach this point. As you pass it, say “Committed!” Then concentrate fully on landing. At this stage, nothing else matters much anyway.
The assumption here is that the landing is being complicated by unfavorable winds, tailwinds, crosswinds, or both. Consider this: there is no law that says you must land at the same strip you took off from. Perhaps there is another strip in the area that may be longer or oriented more favorably, and we could even hope for one free of obstructions at the ends.
Especially consider going to an alternative strip if after repeated missed approaches and go-arounds you are still up there. By this time you will be a nervous wreck, so the time it takes for you to fly a few miles to another strip will give you a chance to calm down. The pressure builds after repeated, unsuccessful landing attempts, so going somewhere else is good because you get to start over!
In this case, don't forget any real airport that may be nearby. You know, the ones with the long, paved runways and a gas truck. Why not go there? It's a simple matter to use your cell phone (You DO always carry a cell phone!) to call someone to come pick you up after you tie your plane securely to the ground. And, yes, you do have enough fuel on board to get there. No UL pilot flies around low on fuel. And also, those big airports usually have restroom facilities that you will probably appreciate.
Committed to landing, running out of runway
If you're still in the air, high and fast, with more than a few feet of altitude left, a quick slip can sometimes save the day. But consider this only if your piloting skills are up to it. Expert pilots can slip a plane safely almost right to the point of touchdown. A less agile pilot can wreck in short order by trying a slip close to the ground.
Ultralights are low-inertia aircraft that tend to slow down quickly once the wheels touch the ground. Therefore, the thing to do is to fly it onto the ground and hit the brakes. However, don't slam it onto the ground so hard that it bounces back into the air! A bounce will only carry you farther down the runway. If you bounce in this situation, the chances are pretty good that you're going to wreck.
If you are firmly on the ground, braking hard, but obviously are not going to be able to stop before going off the end of the runway ... keep on driving! Stay with it! What are you going to hit? If you keep the plane under directional control, you can then choose whether to hit the big tree on the left or the small one on the right. Or even better, go between them. Or if you're going to hit the fence, at least don't hit a post!
This is where familiarity with the terrain off the end of the runway pays off. Look it over ahead of time, perhaps while taking an evening stroll with someone special, and think about the best course of action in the event of over-running the runway.
Committed to a departure, trees getting tall quickly
This is one of the least desirable situations a pilot can imagine being in. The pucker factor goes off the scale. Stay with it; fly the plane.
If you're in a tailwind situation, keep the nose of the plane down so you build airspeed as rapidly as possible. By doing this, you will get to the trees sooner, which is to say the wind will have less time to blow you toward the trees. Then, as you near the trees, pull up rather sharply and hopefully zoom up over the trees.
Once you clear the trees, it's not over yet. What about the airspeed? You will lose airspeed during the zoom. Get the nose down immediately after clearing the trees. Plan to do this. Don't let it be something you have to think about in the heat of the battle. Just don't clear the trees and then dive back into them because the “book” said to lower the nose.
You will know well in advance whether the zooming maneuver is likely to work. If the situation looks really bad, abort! Cut the power, get the plane back on the ground, and hit the brakes. Then while riding the brakes and driving for all you're worth, amuse yourself by selecting the site where the crash is to occur. It's better to hit the trees traveling horizontally on the ground than to stall above the trees and drop in nose first.
This assumes fairly hospitable terrain between the end of the runway and the trees. If it is totally unfriendly, like big rocks, stumps, and the like, hold the plane in the air as long as possible so you land at the slowest possible speed. Just don't stall and drop it in, nose first. As long as you have control, you have some choice in the eventual outcome. Your choice may be between hitting a big rock or a small one, but if you stall, you relinquish even this.
Articles such as this invariably come across with a negative flavor. Flying is supposed to be fun, magic, and wonderful. And it is. But we realize that there are risks involved and we accept those risks when we get into the cockpit and fire up the engine.
My feeling is this. It is not wise to pretend the risks aren't there to the point where a person remains ignorant of what can go wrong and where the pitfalls may be. Likewise, it serves no useful purpose to focus unduly on what all can go wrong.
Some pilots seem so worried about safety and every possible thing that could mess up that I wonder why they ever fly at all. If it's such a burden, why do it? Somewhere in the middle there is the proper balance, which may not be at exactly the same place for each pilot.
As a matter of pride, I believe a person should hone their piloting skills to the maximum degree. Fly as often as possible and learn all you can. Give your plane only the best care and attention, be systematic and thorough in your preflight, and try to cultivate good flying habits. Fly with more experienced, respected, and competent pilots as often as possible and see how they do it. Learn from them, and enjoy the ride. Admit your limitations and try not to exceed them. Try not to be stupid.
Finally, “Tailwinds to all!” But only the smooth kind, at altitude, on long cross-country flights.
Author: Doc Green