When should the throttle be closed on a C172 while landing?

Question

during landing training in a cessna 172, would you rather cut the power to idle at beginning of runway threshold, or idle when you're close to ground? I keep having problems where I flare too high or the plane bounce when it touch the ground, flaring is quite difficult.

Answer 1

Sounds like an improper flaring technique, height perception at the roundout and/or improper final approach speed.

You should always be flying a stabilized approach ie power set to maintain Vref, aircraft configured to land and trimmed correctly to neutralize control pressures on final. Vref should be at the value recommended by the manufacturer, or not greater than 1.3 times the stalling speed in the landing configuration. Configured to land, this value is approx. 61 KIAS in a Cessna 172 as indicated in the POH. You should fly this stabilized condition, on glide path and on centerline all the way down final to the start of the roundout.

You will start the roundout at approx 10 ft above the runway, smoothly pulling power to idle while simultaneously applying back pressure to both arrest your descent and compensate for the loss of lift and elevator authority due to decreased propwash over the wings and tailplane. Judgment of how high off the ground you are is based solely on perspective. You need to use you perspective from your entire field of view, not just how the runway appears, to judge height above the surface. We can practice this in a exercise I will describe below.

The key to our control inputs here is that we want to command the airplane in such a way that it 1) arrests your rate of descent so you arrive at 1-2 feet above the runway with 2) the airplane in the correct attitude to gently make contact with the runway surface on its landing gear. This takes a bit of practice to develop the hand-eye coordination based on the kinesthetic feel of the airplane and control feedback to get this right.

The best exercise to practice this with is the low approach followed by a go-around. NOTE WELL: this is a dual instruction only exercise and should never be performed by a student pilot on solo flights. In this exercise, you will fly a final approach to roundout as you normally would for a landing but not pull the power during the roundout. This will cause you to enter a low approach, flying in ground effect, down the runway centerline at approx 1-2 feet above the surface. With power still set for that used on final, the airplane should ‘float’ in ground effect down the runway. You will continue to fly in this low approach for about 70% the total length of the runway before executing a go-around. Be sure to note the total length of the practice runway during your preflight and establish with your instructor where you will being the go-around to ensure safe obstacle clearance during the departure back into the traffic pattern.

It’s a good idea to select an untowered airport with low traffic and a long runway available to give you plenty of uninterrupted practice and time in the low approach to get practice in this environment. Your instructor can recommend some airports nearby that can offer a good training environment to do this at.

This exercise gives a student pilot a good opportunity to safely practice, when conducted on a dual flight with a CFI on board, the following skills

• Judging height above the ground by perspective alone. During this exercise you can call out the with you are at both the proper height for the start of the roundout as well as established 1-2 feet above the runway, and the instructor can offer feedback, whether he/she concurs with your judgment and make corrections, providing you with the correct sight picture in during roundout.(NOTE: prior to beginning a training session using these techniques, a student should carefully study the perspective from the cockpit while lined up on the runway prior to takeoff and mentally photograph this perspective as his/her reference of the correct roundout height. This is also an excellent technique for tailwheel airplane pilots practicing three point landings because it not only gives the correct height perspective but what the correct 3-point pitch attitude should be at touchdown).
• Maintaining height above runway during slow flight and judging whether the aircraft is maintains altitude or whether you are descending towards the runway or ‘ballooning’ back into the air due to incorrect, insufficient or excessive elevator input.
• Controlling the aircraft in ground effect during slow flight. While students are taught slow flight techniques at altitude, the standard exercise does not provide the feel of the airplane in ground effect.
• Maintaining directional control, runway centerline alignment and proper attitude in a crosswind during the roundout.
• Executing a proper go-around during the roundout and how to mitigate slow speed and/or high AoA hazards in this regime.

Once a student has mastered these techniques, they can attempt to do another low approach to go-around, but once established in the roundout, correctly controlling the airplane, the instructor can smoothly pull the throttle to idle while the student maintains the correct roundout attitude. The student should be warned prior to this to be ready to add additional back pressure once he/she senses the throttle being reduced to idle power to compensate for a loss of lift from reduction of propwash and prevent the airplane from quickly sinking to a firm landing or wheelbarrowing. If this is done correctly, and the student maintains the correct roundout attitude and altitude, the airplane should quickly be exhausted of airspeed and gently settle onto the runway on its main landing gear. We then transition into a high speed ground roll. With addition practice, the student can learn to coordinate throttle reduction and elevator inputs so they can reduce power to idle at the same time they start the roundout.

One final note, unless you have an emergency, never attempt to force an airplane to land if it does not want to do so. If, for any reason the airplane won’t settle down onto the runway, the flare balloons excessively or other excessive floating happens just execute an immediate go-around. If you have fuel on board and all systems are functioning correctly, you have time for another attempt. Sometimes landings, for whatever reason or other just don’t work out and it’s just best to go around and try again.

Hope that helps as it come from someone who struggled with landings and realized no instructors were teaching these skills worth a damn.

Answer 2

The amount of power during landing a 172 only has to do with your angle of approach to the runway.

on final approach/flare/landing airspeed control is critical

Pitch (trim) controls airspeed, power controls your aiming point

So, if you are doing a 3 degree power on approach at 65 knots try cutting power smoothly as soon as you round to level with the runway at around 10-15 feet. Then allow speed to decay as you pull the nose up. After that the plane should almost land itself.

When learning to land "walk before you run"

If you get a good roundout, flaring should be not problem. When coming in to land, arresting your descent at the proper height over the runway is the number one priority$^1$. When learning, it makes no sense to overcomplicate this crucial step. Only chop throttle when you reach 10-15 feet off the runway. Then flare and land.

Be patient and keep flying it until the nose comes up. Practicing on a longer runway is very helpful. You have to know when your plane wants to land. Forcing it at too high an airspeed can cause bouncing or skipping.

Be ready to go around. Practicing rounding out and flaring at the proper height will make perfect. This is why carrying 65 knots gives one a few more precious seconds to get "in the landing groove" before flaring and touchdown. For now, leave that throttle alone until you are properly rounded and on the centerline. Land (safely) a few hundred feet further down the runway. When you get to short field landings, proper rounding becomes more critical. Work on it with your instructor.

$^1$ at this point most of the altitude energy is gone and airspeed is decreasing. Ground effect helps some here, but (if you don't go around) one way or the other the plane is going to land.

Answer 3

My instructor sent me a Rod Machado video on when to flare using visual cues from runway (The Runway Expansion Effect on YouTube). Rod also explains when to reduce throttle.

It first helps to understand perspective which, according to Oxford, is defined as “The art of drawing solid objects on a two dimensional surface so as to give the right impression of their height, width, depth, and position in relation to each other when viewed from a particular point.“ In our case, it is a matter of paying close attention to the relative size of the closest portion of the runway to the furthest point. Thinking of your windscreen as a canvas.

Here are the main visual cues:

• Maintain the landing point in a fixed position in the windscreen.

• Notice how the beginning of the runway flattens out and widens faster as you approach.

• The expansion grows geometrically (increases at an increasing rate) even though your rate of descent is constant.

• Once runway is assured, reduce throttle smoothly to idle.

• Round out should occur followed by flare when runway perspective rate increase is 10x/sec.

Things to note:

• Must have a stabilized approach no faster than 1.3x Vs (velocity of stall)

• Review above mentioned video

• Watch other landings to understand perspective rate of change

• Use a simulator to experiment safely if available

• Discuss with instructor and/or other pilots

Hope this helps

Answer 4

When I teach in the old taildraggers,(65,75,85 hp) I suggest cutting power on down wind just before turning base. About every 30 seconds, I move the throttle forward to keep the engine clear and to ensure that I still have power if a go-round is necessary. It is good practice to do this from time to time in newer aircraft. If you are flying a Piper single and not using carb heat in the pattern, be prepared for carb ice.
With steady winds, chop the power when you know the runway is ‘made’. Then just “hold it off—hold it off” till the mains touch down. The nose should be somewhat high. Ease the yoke back so that it is full back before the nose touches down.(adjust for gusty winds)

Answer 5

"Cutting power" sounds harsh, but then again you definitely should be at idle way before rounding out is done.

What I did, Step by step

1. Establish stable approach
2. At threshold & about 50ft, start retarding the throttle
3. Start gently pulling the nose up, keep eyes at the far end of the runway
4. Throttle closed, keep attitude such that the plane is sinking towards the rwy. Only smooth steering now
5. As you are a couple of feet from the ground gently add pull to let the plane ease into the ground.

So no sudden cut of engine power at any stage, but a steady pull on the throttle like 1...2...3

I mentioned stable approach, because you are setting yourself up for a mess if you need to constantly adjust power during the final stages of approach. In that case your speed (energy) and approach angle are in a constant state of change, and that state will continue all the way to the touchdown. Or bounce as it often turns out.

Answer 6

• Have a stabilized approach and keep the approach picture throughout a large portion of your final approach. This is where a good landing begins. If your plane’s attitude is too different from what it should be over the aiming point, you’re going to have more troubles managing all the energy and settling the plane down gently.

• Maintain the right airspeed. The POH recommends 55-65 kts. A lot of people aim to be at 60 KTs because it’s halfway and seems ideal: I personally prefer to aim for 62.5 kts. Above 65 is too fast. But over 60, even being at 65 is just fine. The slower you are, the sooner the airspeed is gonna fall when you cut the power but you have to still go through the round out and flare stages- and that’s when the plane hits the ground harder.

• Know your aiming point. I was taught to “cut” the power as I’m “crushing” the aiming point. Please be gentle while closing the throttle: the abruptness of pulling the throttle back is directly proportional to the abruptness of the right yaw you’ll get after that.

• When you flare, be gentle and look at the end of the runway: you should be able to see the runway going down as you pull back. Spend time on dual flights to better your judgement of the right amount of asphalt you should see in your viewpoint as you flare. Or find any other reference that works for you. You can even talk about this on the ground with your instructor.

• It’s paramount that you round out in to CRUISE attitude. Any lower and closer to the ground and you risk porpoising. Any higher of a pitch and you risk a tail strike as you keep pulling afterwards. I’ve had both of these. So speaking from experience.

Personal note: For a large portion of my PPL training I was too scared to wait before reaching a good height above the ground to flare at. So naturally my instructor was a bit frustrated with me not being able to let go of the habit of flaring too high (he hid it well though). And the onset occurred after I soloed and started using full flaps instead of 20 degrees. Try your best to get out of fears like this: that helps. And confront these fears. Acknowledge these and actively work on getting rid of these.

Good luck!