Throttle technique during landing

[Desert Strip Basher]

An instructor informed me that they consider throttle should be reduced to zero by the threshold (soft field technique accepted), ie before the flair. Is this normal? Most people I know have always left a little bit of juice on until just prior to touchdown.

[mad_jock]

Yes it is completely normal to do this as all your preformance is calculated with this in mind.

Those that haven't been taught properly or are talent limited prefer to keep a bit of power for various reasons but mainly because it makes it easier to do a greaser. Most of the time though the landing maybe softer but you will use stupid amounts of runway in the process.

A good landing is one that is the right place at the right speed and is within landing limits of rate of decent. One that is a greaser and has touched past where you were intending to touch down is by definition a ****e one.

You can get greasers by doing everything properly it just takes a bit more skill.

[Tinstaafl]

To add a little bit to what MJ wrote, most light aircraft's landing performance charts will specify the conditions & technique used to achieve the distances. Typically it involves power off by 50', as well as configured, stable & at the correct speed.

It's certainly possible to land in less than the book figures using other techniques however you risk losing some safety margins and possibly insurance coverage.

[hugh flung_dung]

Several points:

• the optimum short field technique requires power to be on until the aircraft is in the landing attitude and near the ground - when it's removed the aircraft promptly lands.
• when power is reduced in a propellor driven aircraft the slipstream over the elevator decreases. If you do this at the start of the flare the nose tries to go down just when you want to raise it, that's why it's widely taught to smoothly reduce power whilst raising the nose to the landing attitude. Those who are familiar with landing Seneca 1s and similar aircraft with a forward CG will understand this.
• what has insurance got to do with anything in this context?

HFD

[mad_jock]

Not all aircraft have a low elevator!!!

The mighty Tommy and Seminole are examples.

[FlyingForFun]

Surely it's type-specific, as recent posts suggest?

In the Beech Sierra, as soon as you go to idle power, it drops like a stone. (It does that whether you're at 5000', 50' or 5'.) To get a landing that doesn't break your back, never mind the undercarriage, you have to leave the power on until you're in the flare.

In most other types I've flown, reducing the power smoothly as you start the flare achieves a prompt, smooth touchdown in the desired place - so long as you have the right speed.

It would be nice if the POH described the appropriate landing technique, but most POH's I've read have something fairly vague like "SPEED - SET. THROTTLE - RETARD", with no clue as to where to carry out each action. This is one reason why checkouts on type are a good idea!

FFF
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[Cows getting bigger]

Throttle is an aircraft control, not an on/off switch that should always be activated at the same stage of landing. It should be used in unison with, and balanced against, other controls in order to effect a safe landing.

[Tmbstory]

Throttle on Landing

Cows getting Bigger:

Your comments on the subject are correct. I agree 100%

Tmb

[mad_jock]

I think we maybe need Gengis to confirm the certification standards.

But all GA types should be able to do it.

The orignial OP's instructor isnt wrong in what they say. And personally as long as the person is back at flight idle or idle power before lifting the noise through the horizon to flare I won't say anything. It does require more skill than keeping the power on and if the student is being forced to carry out 3 deg approaches it may make it nearly impossible. Which is another point instructors forcing students to fly C150's in the same style as a Jet with no doudt adding 5knts on to the approach speed due to instructor incompetence, 10 on for gusts and another 5 knts on for mother. Stick some power on in the flare and you have a whole heap of energy to get rid of that the performance never catered for.

[Cows getting bigger]

A couple of extra thoughts:

Energy (speed) control is the most important bit of landing.

The CAA (and I guess other NSAs) recommend a 1.43 fudge factor for landings. I would offer this caters for the vast majority of people who aren't able to nail certification requirements.

[mad_jock]

Where do you find that?

And whats the 1.43 referenced to?

If the UK CAA has any issues with approach speeds they used to issue a change to the POH gawd knows what happens these days though.

If the power is even slightly cracked open it has a huge effect in ground effect of eating up the runway.

[mrmum]

MJ

I suspect CGB is referring to the aircraft performance safety factors from CAA Safety Sense leaflets (and other places). This recommends a 1.43 multiplier as a final safety factor (if aircraft flight manual data is unfactored) for landing distance.
Although it may not be entirely to compensate for pilots who can't maintain the correct approach speed/technique. It could also allow some margin for changes in temperature, wind, surface wetness from those used for the pre departure calculations.

[mrmum]

Approach speeds

The orignial OP's instructor isnt wrong in what they say. And personally as long as the person is back at flight idle or idle power before lifting the noise through the horizon to flare I won't say anything. It does require more skill than keeping the power on and if the student is being forced to carry out 3 deg approaches it may make it nearly impossible. Which is another point instructors forcing students to fly C150's in the same style as a Jet with no doudt adding 5knts on to the approach speed due to instructor incompetence, 10 on for gusts and another 5 knts on for mother. Stick some power on in the flare and you have a whole heap of energy to get rid of that the performance never catered for.

MJ
While I agree with the general sentiment of your comments and I do come across people who fly their approaches way too fast, as you say having decided to add 5kts for this, that and the other over the years. It's not always wrong to add a sensible factor on occasions.

From the PA28 POH

In high wind conditions...it may be desirable to approach...at higher than normal speeds...

A common rule of thumb would perhaps be to add half the gust factor. The problem often is that once a PPL holder has done this, they "forget" to not do it for more normal conditions, but then add a further increment in the future and the effect becomes cumulative, then as you say they waste hundreds of metres of runway having to get rid of all that extra energy.

[Contacttower]

I'm not an instructor but HFD's description seems to be closet to what my understanding of the correct technique is.

Certainly in the C182 if you want to nail the land distance as short as possible that means coming in right on the POH figure, if one were to cut the power completely at 50ft when doing c.60kts then the aircraft would drop rather quickly. Depends on the height one comes over the threshold though, if I wanted to land short I wouldn't come over at 50ft - in a light aircraft that just seems unnecessary - I think what most accurately describes it is the power being reduced as one comes over the threshold but passing to idle pretty much simultaneously with the landing attitude being selected.

Also when in a heavy headwind I find cutting the power significantly before the flare means a much steeper glidepath towards the runway which in turn I find screws my visual perception of the flare a bit!

[Teddy Robinson]

no right... no wrong ...

Good points raised here, my personal take is this.

Object of the exercise is to arrive over the nominal 50 foot barrier at the book speed for type +/- gust factor power on or off.
What we want to do is to achieve is a safe landing: the definition of that varies with type, but the aircraft SHOULD be allowed to enter the zone of nose high pre-stall sink in the correct attitude prior to touchdown on the appropriate bits of rubber.
This ensures the impact is at least nose high, and positive avoiding the embarrassment of bent nose wheels, propellers or whatever and applies equally to a shiny jet as to a microlight.

TR

[Pilot DAR]

Though I do generally agree with MJ, and support the idea that approaches are often flown with power, too fast. Pilots use power as a crutch in place of good technique power off. I do. I cannot completely agree with:

Stick some power on in the flare and you have a whole heap of energy to get rid of that the performance never catered for.

Yes, these words can be correct sometimes, but if you've got yourself behind the power curve, and you're dragging it in, your energy is already at a minimum, and you don't have much to loose. Some recent circuits I was flying in a Twin Otter with full flaps, reminded me of this. Certain planes just "feel better" carrying some power. I'm not saying that is right, but I agree that's the way it might feel.

If the student is using power in the flare to hone his technique, toward becoming skilled with power off flares, that's okay, as long as the end objective of good power off landings is not lost in laziness. I think that is better as a confidence building, learning aid, then a power off approach, during which a whole bunch of power is fed in at the last minute, in an attempt to fix a mess, and then you have a sudden configuration change on top of a poor flare, and still a mess. I was right seat to this in a 172 a few weeks back. Once the power was off, he should not have touched it, he just distracted himself, and forgot to fly the plane for a moment.

I had to familiarize myself in a Piper Navajo recently, after a two circuit checkout. Carrying power through the flare "felt better", but yes, at the expense of proper technique, and landing distances as described in the flight manual. (I had oodles of runway) I got myself to the point of confidence where power off was fine, but things in the flare happen faster.

Another thing I reminded myself during this type familiarizing exercise was that by carrying power, I was defeating an important human factors safety feature. For any retractable landplane, you'll probably have a gear warning horn, operated by reducing power to near idle with the gear up. If you don't reduce to idle, and the wheels were up, you wouldn't get the horn. If you'd forgotten the gear, the first and final reminder would be not good.

For those who do water landings, you will find that carrying power will give you better and safer landings. For floatplanes, a bounced landing can be much more serious much more quickly. Carrying power aids in precision, and not changing phases of flight too quickly, so you have time to optimize your technique. A safe power off glassy water landing would simply not be possible.

The applicable certification requirement is:

(1) Immediately prior to reaching the 50-foot altitude, a steady gliding approach shall have been maintained, with a true indicated air speed of at least 1.3 Vso.

(2) The landing shall be made in such a manner that there is no excessive vertical acceleration, no tendency to bounce, nose over, ground loop, porpoise, or water loop, and in such a manner that its reproduction shall not require any exceptional degree of skill on the part of the pilot or exceptionally favorable conditions.

Note "gliding" approach from 50 feet.

Perhaps like parallel parking, we know we have to be able to do it, but we would rather avoid, so we can easily impress ourselves with a nice job. If you can land adequately with power off, you're safe, keep that skill current, and then sneak in a little power when you want to impress your non pilot passengers with a good landing.

For the OP, following your instructor's advice, and concentrating on a properly flown approach would be your best bet. You can learn to be lazy later!

[mad_jock]

Pilot Dar I do agree with your points about using power to polish and keep safe until you have your eye in with a particualr type. And the human factor point is very well made I hadn't thought of that. And I also fly a type that if your even slightly off profile pulling the power off will result in a quite spectacular arrival.

I don't know much about floats but I seem to remember Chuck had some strong views on power settings on landing a float.

The half the gust thing is utterly wrong for GA types it is a high momentum aircraft type rule of thumb which is defined in the relavent POM (Which is Pilot operating Manual in big types) It takes into account the momentum of the aircraft and also the time it takes to spool the engines up. ie you are flying a puddle jumper like a Jet if you use it.

I think people forget that energy is a squared factor of speed even small increases can cause a dramitic increase in the aircrafts energy state. Try working out adding 15 knts to the approach speed of a Vs 55knt Vapp 70knts and see what I mean with how much extra energy you have.

Then work out how many seconds it takes you to decrease to Vs from the 2 approach speeds.

Then stick that back into s=Vs*t +0.5*A*t^2 you can use what ever you like for A just make sure its A is constant for both times you run it. It doesn't take much increase in t (time in the flare) for you to double your distance used. And S is meant to be distance if you haven't seen newtons laws of motion before and use SI units ie meters, meters per second and meters per second per second.

And BTW I am not such a pratt to not admiting that I do fly the occassional approach at Vne and go to flight idle and flare all the energy off configuring as I go. But its always because I have something up my chuff and I know I will be exiting at the far end of a huge runway. And I might add I will use more runway than a 737 doing it as well. But I am fully aware of what I am doing and I can do it properly when things are "normal".

There is nothing wrong with doing things outside normal techniques as long as you understand the implications of doing so. In fact some would say its good airmanship to get to a skill level where you can. But it shouldn't be "normal" to not do the proper technique.

And to add whats all this pish about 50ft barriers!!! your not flying an IFR approach 3 deg glide you are flying a light aircraft not a pref A machine. The instructors teaching instrument approaches have an excuse for doing it. I can't think of one for anyone else.

[FlyingStone]

Originally Posted by mad_jock

And to add whats all this pish about 50ft barriers!!! your not flying an IFR approach 3 deg glide you are flying a light aircraft not a pref A machine. The instructors teaching instrument approaches have an excuse for doing it. I can't think of one for anyone else.

I agree. I never understood why some people claimed you can't commence flare before the runway threshold (provided you have adequate obstacle clearance: e.g. no trees etc.) and touch down just at the runway treshold. It's safe to do, if it's done right and you can reduce amount of runway required - I'm deliberately not using terms landing roll and landing distance, since in this case landing distance extends outside of published LDA (landing distance available).

On the comments about correct approachs speeds, it should be noted that most people that fly approaches way too fast (for example 75 kts on a C172), tend to land at very fast speeds (~ 60kts, still some power applied) and they then have trouble with controlling the aircraft, since it still wants to fly - not to mention the amount of braking you then need to use to stop the aircraft. The sad part of this is, when you ask them why they make touchdown at such high speeds, they say and I quote "flying near stall speed is dangerous and should be avoided". Obviously nobody read the aircraft manual, which in most cases suggest that landing should be made with minimum speed possible (in existing conditions) - I believe making touchdown at 60 kts in clear/still air in a C172 is way too fast, the stall warning doesn't even come on yet.

Originally Posted by mad_jock

And BTW I am not such a pratt to not admiting that I do fly the occassional approach at Vne and go to flight idle and flare all the energy off configuring as I go. But its always because I have something up my chuff and I know I will be exiting at the far end of a huge runway. And I might add I will use more runway than a 737 doing it as well. But I am fully aware of what I am doing and I can do it properly when things are "normal".

And it's indeed very good excercise for demonstrating the effects of flight controls at various speeds. For example, you arrive at threshold (of a runway long enough, of course) at height of ~ 10ft, speed is close to Vne. You retard the throttle and maintain height, you have to slowly trim the aircraft to nose up when you loose speed. When at appropriate speed (Vfe or some speed below that in order to prevent such high loads on the flaps), you start extending flaps, which causes quite a balooning (depends on the type flown) and when your speed reduces to something appropriate, you flare the aircraft and touch down close or at stall speed and you've just demonstrated effects of flight controls at the entire range of airspeeds you can expect in normal flight (albeit in ground effect).

[W.D. Charlwood]

In my day, ALL approaches were glide approaches - commenced immediately after turning onto base leg. Thus, accurate control of airspeed and rate of flare became second nature. The current technique of teaching students powered approaches (and we all know why this is done) leads to future difficulties.

[24Carrot]

Since mad jock introduced the physics into this, and to amplify his point about approach speeds:
Height (potential energy) and speed (kinetic energy) are both just energy, and we all know you can convert between the two by pitching up or down, but you don't often see the equivalents calculated.

At the kind of speeds we are talking about 15kts excess speed is equivalent to about 100 ft excess height. With typical L/D ratios that is several hundred feet of runway, and of course ground effect 'improves' the L/D ratio.

Since excess height is a lot easier to spot than excess speed, isn't this the biggest argument for nailing the POH approach speed from the top of final approach?