Airspeed and flaps relation on approach and landing

3 Answers

1. 
   

   
   

   CarsonAviation on Oct 12, 2019

   As a new pilot, you don’t yet have the skills developed to know where to look, when to look, or what you’re looking at. These skills and habits will come with practice and good instruction from a good CFI and from casual flying with other good pilots who have different habits from yours and your instructors.

   If you haven’t been able to get in a good stabilized approach, the first thing that you can do is give yourself more time. You can do this by flying a wider and longer pattern. More distance = more time to figure out what to do next and to keep up with the plane. As your flying skills get better, you’ll tighten up your pattern and fly closer to the field. When you fly a tight pattern, everything happens faster, and if you haven’t yet mastered the basic physics of a stable approach and landing, the extra time that flying a wider pattern gives you will help you fix your mistakes as they’re happening.

   The FAA’s Safety Team has a decent couple pages showing what a stabilized approach is. (https://www.faasafety.gov/files/events/EA/EA03/2019/EA0392336/Stabilized_Approach_Concept.pdf)

   Chapter 8 of the FAA Airplane Flying Handbook (https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/airplane_handbook/media/10_afh_ch8.pdf) is a good reference and a good place to start to figure out part of the “when” and the “what” that I mentioned above. If your program doesn’t include the FAA Airplane Flying Handbook as part of your curriculum, I would strongly suggest you find a new instructor or school that does.

   You didn’t mention which type of aircraft you’re flying. This can make a difference in your round-out and flare, but the basics of a stable approach are the same for both low-wing and high-wing aircraft. Here is how we do it with a low-wing aircraft at a high altitude airport when the wind is behaving nicely (+/- 20 degree crosswinds with 0-8 kts velocity):

   [1] When you’re abeam your landing point (which should always under normal conditions be the landing zone or “Captain’s Bars” painted on the pavement, and never the numbers unless you’re practicing short field landings), make your first power reduction and RAISE the nose slightly to maintain altitude. Do not start descending the airplane yet. You first need to slow the plane down enough to safely apply your first notch of flaps and stabilize your airspeed at a constant speed. The earlier you stabilize your approach speed, the easier it will be to do all the other things that you’ll need to do with one less thing to worry about as much on the way down. Memorize the RPM setting on the tachometer that gets you the airspeed that you want and always use that RPM setting in the future with that airplane.

   [2] After the plane reaches your intended approach speed, pitch the nose down and quickly trim it to maintain that airspeed. You should be able to find the trim by touch and you should be looking outside while you’re trimming. At this point, you will be descending. Your target descent rate should be right around 500-600 fpm. Look quickly at your Vertical Speed Indicator and verify that you are descending at your intended rate, and that the rate is a constant rate of descent and not changing up and down dramatically.

   [3] Next, check your airspeed again to make sure it’s still on target (+/- 3 or 4 kts). Then, eyes back outside the plane. At this stage, the plane should be gently flying itself forward and downward with no strong control inputs from you. Let the plane fly on its own. It was built to be a flying machine and it knows how to fly better than you do. You should be gently guiding it along, not forcing it to do anything. If you’re having to grip the yoke firmly and provide lots of control inputs, then it’s not trimmed properly. Fix the trim and let the plane fly on its own with your gentle guidance to nudge it along.

   [4] One of the hardest skills to acquire is knowing when to turn to the next leg of the pattern. Many instructors will just give you a landmark on the ground and say, “turn when you’re over this building,” or, “turn just past that road,” or something similar. Often, instructors won’t say anything at all and the student starts picking up landmarks on their own and then makes the false assumption that the pattern should always be flown by turning at the same point every time. This is not a good way to learn pattern flying as it fails to teach you the relationship between your sink rate and the distance required to intersect the glide slope at different rates of descent. Also, later in your flying when your personal minimums start to go up with your experience and you start taking on faster winds and higher crosswind angles, your mastery of your aircraft will depend on knowing how much distance you need to fly for different rates of descent. So, how do you improve this skill of knowing when to turn? You have to practice it over and over and teach yourself how your plane behaves when you try different speeds. A good instructor wants to see you consistently handle the aircraft and they may be hesitant to have you vary your rate of descent early in your training, so almost all your approaches as a student will be flown at the same speed and distance from the runway until you can do them without a large mental effort. A good rule of thumb for when to turn from downwind to base, is when you look out the left side of the plane (assuming you’re flying a left-hand pattern), when the plane is at a position 45 degrees away from the landing point (to your left and behind you), it’s time to turn.

   [5] After you’ve turned the plane onto the base leg, add your next notch of flaps. Do not add flaps while you’re in the turn. Most training aircraft these days have electric flap motors, and if one motor fails, or if one of them runs away and won’t stop, you want to be flying straight and not in a turn. An asymmetrical flap deployment in a turn can lead to an immediate cross-controlled stall, and as a student pilot, you’re not going to have the flying skill to get out of that stall so close to the ground and also to get the flaps sorted out, so just don’t try it. Make it a habit to only add or remove flaps when flying in a straight line– never in a turn. Adding more flaps will add more lift, so you will immediately have to re-pitch the nose to match the new flap setting, and to hold the plane at that new pitch setting, you must re-trim it as well. Why do you have to re-pitch the nose? If you don’t, then the rate of descent that you just had won’t be the same rate anymore. Extra lift from the flaps means the rate of descent will slow down, and you do want a stable approach, so you will have to re-pitch the nose to keep the rate of descent at that constant 500-600 fpm rate. Occasionally, you’ll also have to adjust the power, but most training airplanes in standard atmospheric conditions won’t need many power adjustments if your airspeed is already steady and your rate of descent is also a constant. Do a quick check of airspeed and sink rate and then eyes back outside.

   [6] Knowing when to turn from base to final is much easier than judging when to turn from downwind to base. If you’re far enough out and you overshoot the runway, you should have enough distance to get back on the centerline without having to do a go-around. Once you’ve established yourself on final, you should be looking down the runway to make sure it’s clear, and then focus on keeping the plane on the centerline. Your sink rate and airspeed should already be established, so just guide it down. As you get closer to the runway, if you feel you need to use the last notch of flaps, then add them, but only after you’re sure that you can glide down to the runway if you lose your engine, and never use the full flap setting in strong gusty winds.

   [7] As you cross over the threshold of the runway, you should be backing your throttle down to full idle, and then controlling your pitch to maintain your airspeed slightly above stall speed. If you hear the stall horn go off and you’re more than a foot or two above the runway, pitch down gently to pick up a little airspeed, but do not add any throttle back or you’ll end up floating past your landing spot and using up too much runway. In the last 20 feet or less of altitude, don’t worry about keeping the ball centered and flying coordinated. Focus on using your hands (ailerons) to level your wings from side to side (this is super important in a low-wing aircraft that you don’t let either wing tilt to far side to side and strike the ground). Use your feet (rudder) to steer the aircraft and keep it on the centerline. Most importantly of all, you want both main landing gear parallel with the centerline when they touch down just at stall speed. Never land at an angle across the centerline. This will put too much side pressure on the tires and it won’t end nicely. Although your stable approach has been descending at a constant rate of 500-600 fpm, in the last 50-100 feet of altitude, you want to start reducing that sink rate so that the moment you touch down on the runway, your rate of descent should be almost zero. You want to slide onto the runway and roll out, not impact the runway at a 3 degree angle at 600 fpm downward. The way that you reduce this rate of descent is a combination between the flaps slowing you and giving some floaty lift, reducing the power (throttle) to give you less airspeed, and properly beginning the round-out and flare.

   [8] In both low-wing and high-wing aircraft, the standard technique is to gradually increase the back pressure on the yoke to raise the nose after the main gear have touched down. If you do this too soon or too much, the plane will “balloon” up and come crashing back down hard. This is called pilot-induced oscillation, and it’s really bad for the plane and you can run out of runway if you keep doing it. If you do accidentally over-flare the plane, don’t mess around. Power up and go around and get out of there. It’s way too easy to get fixated on the oscillation problem and not notice the end of the runway and the fence ahead coming at you. Oscillation usually occurs from flaring too early when the plane still has too much speed. I’ve also seen it happen when there’s an intersecting runway with residual vortices still floating around from previous take-offs from other planes as you fly through it. Think about the forces that you’re putting on the plane. Most training aircraft weigh almost around a ton, and if you dropped a ton of weight off a crane at just five feet high, you should expect bad things to happen. Planes are no different.

   [9] If you did get a good landing, most training aircraft are forgiving enough that you can continue to taxi down the runway and exit onto a taxiway with full flaps deployed. In our situation in the mountains with low-wing aircraft that have manual flap controls, we encourage our students to retract the flaps as they roll out on the runway. In our environment, we get constant crosswinds all the time, and maintaining lateral control with full flaps deployed is really difficult and you can get pulled off the side of the runway if you’re not careful. Also the Piper POH recommends that we remove the flaps as soon as we can when landing so that we can stick to the ground better, as taking the flaps away takes away lift exactly when we don’t want any more lift. Many instructors, especially in Cessnas, teach you to wait until you clear the runway before removing the flaps. This usually doesn’t make a difference to us where we are since the Cessna flaps don’t really do much when you’re on the ground, but the Piper flaps are very affected by crosswind since they’re so close to the ground in the low-wing designs that Piper uses.

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2. 
   

   
   

   Warren Webb Jr on Oct 14, 2019

   CarsonAviation is referring to the best training guide in the world (FAA Airplane Flying Handbook) but inexplicably not following its recommendations or concepts.

   The RPM setting is different for each pattern and approach – not the same. In the traffic pattern, the airplane should be at an appropriate airspeed for each leg. Conditions (density altitude, winds, aircraft weight) can vary a huge amount from day to day. Therefore the power needed to maintain the desired airspeed on downwind, base, and final will always vary. Think about what you do in your car – do you apply the power for a value of the rpm or the speedometer? In the airplane, adjust power as needed for the desired airspeed. RPM is not mentioned in the sections in chapter 8 on the landing descent so it is an improper reference.

   Do not look at the Vertical Speed Indicator. The correct vertical speed on one approach means nothing for the next approach. If the winds increase and reduce ground speed, the next approach must be flown at a lower rate of descent and vice versa. The correct rate of descent can only be determined by looking at the aiming point to assure the airplane is not over or under-shooting.

   The preceding two paragraphs above are the primary basics of the landing descent – monitor the aiming point and keep the airplane descending to that point with the elevator – simultaneously use the power to keep the desired airspeed. Don’t get into the trap of any rote pitch and power settings – learn the above techniques in the Handbook from the beginning – they will automatically allow for all variable conditions including flying different airplane makes and models, including jets. The main objective as stated in Chapter 1 of the Handbook is to learn universal skills.

   Turns to the next leg are one of the easier skills. Training in ground reference maneuvers (Chapter 6) should precede landing approaches and will prepare you for flying the entire pattern.

   Flaps – complete the final flap setting after turning final as recommended. A change in flaps close to the runway will de-stabilize the approach. This has been emphasized to me personally by FAA inspectors.

   Coming over the threshold, the roundout is performed with the elevator controlling altitude and rate of descent (by visual reference to the runway) – not the airspeed. “Lift is controlled so the airplane settles gently onto the landing surface”. “In some cases, it may be necessary to advance the throttle slightly to prevent an excessive rate of sink or a stall, either of which results in a hard, drop-in type landing”.

   In normal landings, don’t retract the flaps until “the airplane has slowed sufficiently and has turned on to the taxiway and stopped”. Raising the flaps on the roll-out is a big distraction.

   In item 7 regarding the last 20 feet – the feet do not keep the airplane on the centerline – the ailerons do. If the airplane moves to the left or right with respect to the centerline, the bank needs to be adjusted (rudder is used for wheel alignment only).

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3. 
   

   
   

   Mark Kolber on Oct 20, 2019

   Flaps allow for a steeper descent at a slower airspeed. Other than that, they are *not* speed brakes, should not replace good airspeed control using pitch and power, and have little to no relationship to the smoothness of your landings.

   Smoothness comes with two things, both related to experience. One is simply practice in selecting an airspeed and controlling it and your descent rate.

   The other is anticipation – what we call staying ahead of the airplane. Once stabilized at selected airspeed and altitude on downwind, for example, your thoughts move to the steps you will need to take when you reach the abeam touchdown point. “When I get there,” you might even say out loud, “I will reduce power to X, slow to Y, put in first flaps and begun a descent at Z feet per minute.” Then, instead of trying to figure all that out in the second when you get there, you have prepared yourself to simply do it. Do that for every leg from pattern entry to touchdown.

   That’s not easy. It’s probably the single most difficult thing a new pilot learns. But it pays huge dividends. And not just for landings

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