Landing Flaps: Full, Partial or None?
Want to start an argument on an online aviation forum or while having a $200 hamburger with your buds? Express an opinion on flap use on landing in a light single. The responses you’ll get are aviation’s form of red states versus blue states.
The no-flap or partial-flap crowd points to a number of Owner's Manuals and Operating Handbooks that repeat a phrase which says something along the line of using the minimum flap setting for the runway length on landing. They correctly point out that the pitch change from the final approach glide in the flare is smaller without flaps and so it is easier for less-experienced pilots to make a landing. It is easier to get the airplane lined up on the runway in a crosswind because of the extra airflow over the control surfaces. It is also easier to make a go-around from a partial- or no-flap approach. They say it is hard to judge the flare when descending so fast, power off, with full flaps. Besides, the partial-flap crowd points out, on many airplanes there is only one knot difference in the stall speed between half and full flaps.
The other side of the argument tends to be that using full flaps results in a slower touchdown and less bouncing around in gusts because the added drag helps stabilize the airplane. Proponents add that the flaps are on the airplane for a purpose, not decoration, and it doesn't matter that you come down final with lots of airflow over the control surfaces, sooner or later you have to slow down and lose that airflow. They also point to the POHs for the Diamond-series singles, which call for full flaps on landing—and note that the landing accident rate for Diamonds is so low as to be nearly nonexistent.
So, What do we have?
It's true, for pre-solo pilots sorting out the problem of trying to keep all those monkeys under the bushel basket, the touchdown part of a reduced- or no-flap landing is easier to learn. A good instructor will have the student configure the airplane for landing in a way that minimizes distractions and lets the student concentrate on hitting that there runway. Only after the initial skill is gained does a good instructor start teaching the more complicated landings, such as short field, soft field, wheel (for tailwheel airplanes) and crosswinds.
Which Is Better, Full Or Reduced Flap Settings On Landing?
I'll give you the lawyer answer: It depends. However, the accident data indicates that, in most circumstances, you are better off with full flaps.
My opinion on the subject began to form during some days of research when I was flight instructing in college. I got interested in landing accidents, read a boatload of accident reports and found that where flap deflection on landing was recorded, the landing accident rate seemed to be inversely proportional to the percentage of available flap being used. That is, the more flap deflection used, the fewer the number of accidents.
I also noticed that most landing accidents were really rollout accidents. The pilots almost always managed to get the airplane onto the runway, then lost it during rollout.
After years of wrestling with just trying to hit the runway, the fact that the loss of control occurred later on was an eye-opener. The real problem with a "landing accident" was not control of the airplane in flight. It was loss of control after touchdown, both on tailwheel and nosewheel airplanes.
Because of those days of looking at accident reports, I've tried to pay attention to the flap-selection-on-landing issue over the years. I've listened to a lot of arguments, read articles, watched one crash involving loss of control after landing and looked at a few airplanes that had run off runways. As a result, I've formed some opinions on the use of flaps on landing. They may be imperfect, but they were not arrived at hastily.
1. The cause of most landing accidents, no matter the wind condition, is not control of the airplane on final. While the cliché about a good landing following a good approach is pretty true, as an instructor I see a lot of pilots, usually not student pilots, who are uncomfortable slowing the airplane down on final. They tack on extra knots for the spouse, the kids, the relatives and their favorite Netflix series. Excess speed, combined with the low wing loading of light singles, causes them to float and start having problems with drift as the speed finally bleeds off and the flight controls begin to need more and more deflection. Or, they notice that they are running out of runway. The next step seems to be for the pilot to stick the airplane on the ground quite a bit above its stall speed. Sometimes the first part of the aeronautical anatomy to make contact with the runway is the nosewheel.
2. The resultant landing accident is caused because there is less rolling control than the pilot anticipates. There is pretty good aerodynamic control, but the pilot simply does not use it. The mind-set seems to be that once on the ground the aerodynamic controls are no longer relevant. In addition, just after touchdown there is a huge tendency for nosewheel aircraft pilots to sit back with the "I made it" sigh. Much to their dismay, they discover the airplane doesn't have squat for rolling control when it is zorching along at or above stall speed. It is flying more than it is rolling.
During the early portion of the rollout, flight controls are effective. We've all done slow flight at altitude and noticed that the airplane was controllable. It just took some relatively big control inputs to get the airplane to go where we wanted it. So, after touchdown, it is the flight controls which keep the airplane going in the desired direction, not the wheels. Time and time again, the pilot applies a little aileron, but not enough. The result is a sideways, hopping skid off of the runway into bent metal. Or, the pilot pushes the nose down in an effort to get rolling control, which simply isn't there yet, and makes the main gear even lighter on the runway, slides the tires and goes off the end.
3. There is a window of exposure between the moment that aerodynamic controls lose effectiveness and the wheels develop it. At touchdown you still have pretty good flight control effectiveness if you are willing to use it. It will diminish in effectiveness as we decelerate. When you are rolling slowly you have good control because the weight is on the wheels. That control gets progressively better during deceleration. The idea is to minimize the period where you have neither good flying nor rolling control. How do you do it? Land as slowly as possible, decelerate quickly and put the weight on the main wheels early. Landing slowly means you kept the airplane going in the correct direction in the air through the judicious use of the flight controls. As a result, the flight controls are positioned to help you out on the ground...think of the touchdown as another part of the landing process, not the end of it (fly the airplane until it stops moving, ever heard that before?).
From a behavioral perspective, pilots who fly at the recommended speed down the last portion of final, with full flaps, tend to be in the habit of putting the flight controls where needed and to continue to do so after touchdown. It seems to be a cause and effect situation. Those who fly overly fast down final and need little control deflection seem less likely to use aerodynamic control during rollout and be more prone to wreck airplanes.
Touching down with full flaps gives you the lowest stalling speed. It also gives you an additional benefit: maximum drag so you will decelerate as rapidly as possible with the power off, getting you down through that red zone of poor control, rapidly.
While the FAA may frown on it as a negative transfer of learning and cause you to run the risk of someday retracting the gear during rollout—raising the flaps about one-third of the way into the rollout helps put weight on to the main gear about the time the flap's value for aerodynamic deceleration is running out. (Yes, you have been warned, if you grab the gear handle, you did it knowing the risk, don't jump on me.) You get a triple benefit from using flaps: low touchdown speed, rapid initial deceleration and a lift-dump device for putting weight onto the wheels to enhance rolling control.
But, What About Go Arounds?
Someone always jumps in the discussion and claims that a ________ (just fill in the blank) won't climb with full flaps. That simply is not true for any general aviation trainer made in the last 60 years unless it is a hot day in Denver. If the airplane will not climb with full flaps something is wrong with the airplane or pilot technique.
And, What About Airplanes With No Flaps?
The light wing-loading airplanes with no flaps—other than the Ercoupe—have a fairly high landing accident rate. The no-flap airplanes also tend to be tailwheel machines, which adds another variable to the issue of landing accidents. They are more challenging to control on rollout.
A Down Side To Full Flap Landings?
So what is the down side? The fact it takes more work to line up with the runway and make the touchdown. It requires more skill to land the airplane with full flaps. Looking beyond the seemingly obvious, the fact that it takes more skill to get the airplane to the desired spot on the runway with full flaps is actually a benefit. It tells the pilot when he or she should not try to land on that runway. How so?
Setting up the airplane on final at the recommended approach speed with full flaps and adding no more speed than one-half the gust factor puts the pilot in a very good position to evaluate wind and runway conditions. (Gust factor is the amount over the steady state wind the gusts are blowing. If the wind is reported at twelve with gusts to twenty, the gust factor is twenty minus twelve, or eight. Add half of this value, four knots, to your approach speed, and no more.) Hold the recommended approach speed plus gust adjustment and see if you can line the airplane up with the runway.
If you can’t, that is, you get either the aileron or rudder to the stop and still cannot control the drift—you are getting a message loud and clear. There is good reason to believe you will have significant difficulty controlling the airplane on the rollout. Why buy trouble? That runway may not be a good one for landing under those weather conditions.
If you can keep the airplane aligned with the runway you will have the necessary aileron correction cranked in on touchdown. You can land on one main gear, then go the rest of the way to full aileron deflection as you try to hold the other main off the ground. The deflected ailerons will help you keep the airplane going straight. (Adverse aileron yaw, remember?) The deflected ailerons will keep the upwind wing down and avoid the wind getting under it to flip you over. It also helps put a lot of weight onto the wheel on that side, enhancing rolling friction and control. The flaps will slow you rapidly. As the nose comes down, the flaps can go up and, Yeah, Baby, you have good rolling control and the ailerons are to the stop where they should be. By the way, you have saved wear and tear on tires and brakes.
Keep in mind that in this situation there is no magic to the centerline of the runway. If there is a lot of crosswind and lining up with the centerline is proving difficult, consider touching down on the downwind side of the runway and angling across it slightly, toward the wind, to effectively reduce the crosswind angle. It’s only a small improvement in the angle, but you might as well take advantage of anything that may improve the odds available to you.
I Can’t Line Up With the Runway
Ok, you did it right, but still can't line up with the runway with full flaps. The wind is too strong. What do you do? First, remember you are the pilot in command. You select a runway which is more into the wind. It may be grass. That may be why they built a short grass runway at that airport, for those strong crosswind days. Haven't landed on grass? Why not? Go do it.
The next option is to go to another airport with a runway aligned more into the wind. So you have to arrange ground transportation? It is far less embarrassing than arranging to repair a bent airplane. I've checked.
If you do not have the fuel to get to another, more suitable airport consider two other options:
1. Is there a taxiway oriented into the wind? Is it long enough to land on? With a strong wind it may not take much distance—you’ve landed in strong headwinds before. You are in a situation where control of the airplane is in doubt because of the strength of the wind. Questionable control defines an emergency situation. For crying out loud, use your judgment; landing on a correctly aligned taxiway of suitable length may be the safest thing to do. There’s no FAR that prohibits it. Even if there were, in an emergency you may deviate from the regulations to the extent necessary to deal with the emergency.
2. As an alternative, if you have practiced it recently—and I mean practiced—you might try a portion of the Bob Hoover Tennessee Waltz landing. Come down final with the flaps up and enough speed to keep the airplane aligned with the desired track on the runway in a side, not a forward, slip. Flare just enough to keep the nosewheel from touching down, then touch down on the upwind main landing gear. This is the nosewheel version of a wheel landing in a conventional gear airplane. Keep the airplane on that wheel, power off, as long as you possibly can. That means you will progressively move the control stick or wheel all the way to the side and aft. Only after you have full aileron and elevator deflection will the downwind gear and nosewheel touch. At that point you can relax the elevator pressure a bit, but not the aileron. You've done all you can with the flight controls, keep them there and hope you can keep it straight until the wheels quit sliding sideways and the tires get some bite.
Am I being inconsistent by suggesting a landing with no flaps after a long discussion of the benefits of full-flap landings? Perhaps. The flaps-up landing increases the loss of control exposure on roll out. The idea is to get the pilot's full attention focused on what’s important—the crosswind and the need for full aileron deflection after touchdown before making the conscious decision to land the airplane flaps-up. Then, and only then, is the pilot ready to do what is necessary to put the airplane where desired and not be a passenger.
Rick Durden holds an ATP and is a CFII and is the author of The Thinking Pilot’s Flight Manual or, How to Survive Flying Little Airplanes and Have a Ball Doing It, Vol. I.