Glide path control on final.

[boofhead]

I get into discussions with instructors and others and usually find myself to be outside normal thinking, but this one I can't let go of. I see students screw up landings because they cannot fly a final approach. They do not know how to get onto a correct glidepath and canot maintain one even if they recognise it. The particular bane is the student (and some of these guys/girls are commercial pilots) who lets the nose come up approaching the runway and loses speed, then has to dive for the runway or drops on in a partial stall.
The traditional advice is to use attitude for speed and thrust or power for glidepath. But that does not work on an ILS, except in a very rough and ready manner, since the response is too slow, so I have always flown the glidepath with attitude (elevators) and maintain the speed with small changes in thrust.
Most variations from the normal glidepath are pilot induced, so that if the airplane goes a little low, the speed will be a little high as a result. Getting back on the glidepath using elevators will simultaneously correct glidepath and speed.
Of the two parameters, speed and glidepath, glidepath is the more important. The airplane can safely land if a little fast or slow, but it cannot safely land if the landing is short or long.
Many pilots don't seem to give a damn about where on the runway they land, so long as there is tarmac under them, but I like to teach my students that there will not always be excess runway available and they should make every landing as a precision landing.
And a glider does not have power to adjust the glidepath (sure it has speed brake but I am sure most glider pilots do not pedal their way down final with that control).
I therefore teach that when on final, the pilot should establish the glidepath and speed, and maintain the glide path using elevator, adjusting power as needed to control airspeed. For every airplane, not just the B737.
Some of the junior instructors I have spoken to about this claim I am talking heresy, but cannot give me a sporting argument.
I am not talking about normal descents or climbs, just on final. If turning base you see you are high, of course drag back the throttle or select flap early, and if low, push the throttle forward. I am only speaking about a glide path, whether electronic or visual.

[DB6]

You'll get a sporting argument on here, boofhead! Do a search for 'point and power' and you'll find a lot of stuff already written. I'm with you though for the simple reason that P&P works in any aircraft, big or small, whereas attitude for airspeed won't if you have to maintain an accurate glidepath in anything with reasonable inertia.

[Cows getting bigger]

Point and power is a valid technique that many students warm to. Indeed, I think that most of us develop the technique with experience although, as stated on a previous thread, it's all about the elastic band connecting the left hand to the right. Shooting off at a bit of a tangent, one of my favourite niggles is the ability for a student to completely Horlicks a great approach by killing the power as they cross the threshold, thus demanding a rearwards lunge on the elevator as the nose pitches down rather rapidly towards the ground.

[DFC]

It does not matter what flight path we are talking about be it descent, cruise or climb, it all comes down to the four forces acting on the aircraft in flight.

People fail to understand the difference bewteen flight path - the path through the air that the aircraft is following and attitude - where the nose is pointing.

It is usually only when CPLs transition onto something that flys along a -3 degree path with a +4 degree attitude that they learn to totally separate the two.

Put any aircraft on a 3 degree approach path at approach speed and power setting.

If the aircraft is now moved above the desired flight path and the pilot does nothing the aircraft will parallel the desired path.

To regain the desired path the pilot has to steepen the aircraft flight path. The pilot wants to do this while maintaining the approach speed.

It matters little how you visualise the control movements, it is the same - the flight path is steepened and to avoid the resultant increase in speed, the thrust is reduced.

So do you reduce the thrust - aircraft slows due to drag greather than thrust and then lower the flight path and use gravity to regain the airspeed;

or

Do you lower the flight path - aircraft speed increases due to assistance from gravity and in response you reuce the thrust to regain the desired speed.

Overall, the problem is that many people do not fully understand either way of doing it.

There is no way of getting away from the major principle when flying on the ideal flight path towards your aiming point, if you become high or low then you are going to have to fly a new flight path that intercepts the desired flight path until it is regained. That means that the aiming point will have to change to some point before the ideal point when high and some point beyond if low.

Think of the extreme situation - if you get so low that you have to fly level what are your doing - you are adjusting your flight path to be horizontal (aiming point is the horizon) until you regain the desired approach path.

Having established that we are using different flight paths to correct and maintain the desired approach path then we have to agree that we will use all the controls - flying controls and thrust controls to acheive those flight paths.

The only difference between big and small aeroplanes is that in the big case, due to momentum one can make some small temporary changes in flight path without having any immediate change in airspeed. In something like a small microlight, any change in flight path will result in an almost instant change in speed.

Does this make a difference to how the pilot flies a particular flight path - only in the amount of throttle movements required if one wishes to maintain a very accuarte airspeed.

So forget - point and power or power for height and attitude for airspeed - it is the flight path of the aircraft that is getting you to where you want to be.

For those that argue attitude for speed is safer - can they explain why recovery from the stall enforces reduction of angle of attack rather than increasing airspeed?

Regards,

DFC

[TheChitterneFlyer]

For those that argue attitude for speed is safer - can they explain why recovery from the stall enforces reduction of angle of attack rather than increasing airspeed?

I feel sure that you fully understand all of the principles, but the final statement regarding reduction of angle of attack rather than increasing airspeed (with power) is the basic fundamental for teaching new pilots the art of stall recovery; in fact, they are taught to do both... reduce angle of attack (to unstall the wing) and simultaneously applying power. An advanced flying student, or a more experienced pilot, would of course understand the merits of what we're trying to achieve. However, as anyone will tell you, if you're revalidating your PPL and you choose to carry out stall recovery by the application of power alone... your examiner will fail you!

Our RAF bretherans will tell you that 'point and power' is the technique taught to military pilots; for after all they are (in the main) going to be flying those sharp pointy and slippery things.

I guess that the argument is 'twofold'... we're not routinely expected to stall on the glidepath, so why not use 'point and power' for glidepath control. However, during the final approach phase; revert to 'attitude for speed' and 'power for attitude'. The 'twofold' argument is really only applicable to advanced students/experienced pilots and not for the part-time weekend flyers.

I wholeheartedly agree, that larger aeroplanes (with the attendant inertia) and 3 degree path with a +4 degree attitude require more refined handling skills. Having said that, an aeroplane such as the TriStar was designed for 'point and power' from the onset... too high on the approach path; push on the yoke, where the Direct Lift Control would maintain the attitude but increase the ROD by modulating the speedbrakes.

In conclusion, it all rather depends upon which flying community we're trying to teach! If you designed DLC into a Warrior... well, we'd end up with more accidents!

Horses for courses.

TCF

[DFC]

I feel sure that you fully understand all of the principles, but the final statement regarding reduction of angle of attack rather than increasing airspeed (with power) is the basic fundamental for teaching new pilots the art of stall recovery; in fact, they are taught to do both... reduce angle of attack (to unstall the wing) and simultaneously applying power.

Unfortunately however, very few seem to understand the two totally separate and unrelated things acheived by such actions even when done in parallel.

Application of power has absolutely nothing to do with stall recovery. Stall recovery involves unstalling the wings by reducing the angle of attack. No more and no less.

A PA28, A Glider and a Tornado all recover from a stall in exactly the same way - the angle of attack is reduced below the stalling angle of attack.

Power is simply used to reduce the amount that the subsequent flight path has to point towards earth in order to regain suficient airspeed to a) avoid re-entry to the stall and b) climb away with less drag than one has 1kt above the stall.

With no power, gravity is all one has to accelerate the aircraft.

With full power less use is made of gravity because the thrust accelerates the aircraft and only a very temporary shallow descending flight path is required to regain suficient speed.

People may think that they are recovering from a stall with power alone but they are not - they are simply maintaining a constant (balistic) flight path and ensuring that thrust exceeds drag. As the aircraft accelerates, the angle of attack required to maintain that flight path reduces.

Examiners are quite right to fail anyone that uses any method to recover from a stall other than reducing the angle of attack.

As I said, any pilot flying an approach will be using all the controls incvluding power to maintain the desired flightpath and airspeed. One will say that they are using point and power. Another will say that they are using something else. However, when you sit back and watch they fly a correct approach with whatever adjustments are necessary they both do exactly the same thing with the controls - if they did not then either the flight path would end up being wrong or the airspeed would wander all over the place.

So what we have is simply two camps that do exactly the same thing but think of their actions in different ways.

Regards,

DFC

[Cows getting bigger]

My elastic band analogy?

[TurboJ]

can they explain why recovery from the stall enforces reduction of angle of attack rather than increasing airspeed?

Quite simply you need to reduce the angle of attack in order to allow the air to flow over the wings. Full power is applied to merely reduce the amount of height lost.

Its also important to get the student to reduce the angle of attack of the wings before applying the power as done the other way round can cause the problem to get worse. In certain circumstances I get the student to recover by merely reducing the angle of attack of the wings and then later on introduce the power.

[Cows getting bigger]

When teaching stalls I do exactly that. Stall recovery without power - note altitude loss. Do the same stall but this time recover with power (as well as reducing AoA) and note a smaller altitude loss.

Getting back to PnP or the more traditional method, the reality is as DFC says. To maintain a particular glidepath (an unfortunate word) you may need to alter the picture. If your aircraft is nicely trimmed at approach speed (which it should be) then any attempt to change the picture will require the use of both pitch and power. Which one you apply 'first' is probably something of an academic argument. More interestingly, if your not flying at the desired approach speed then you do have to ask how best to alter the speed. Assuming you are on glidepath in this scenario, the most natural thing to do is alter the power (to change speed) then countering any power induced change of picture with pitch. However, the reality should be that the two actions are coordinated. After all, we do teach students to alter speed whilst maintaining altitude in Ex6, don't we? To me there is no difference between Ex6 and Ex13 as far as controlling the aircraft is concerned.

[boofhead]

I am only talking about the last 500 feet. And only for students or people having trouble with landing approaches.
I consider the most important parameter to be glide path control. Speed can vary a little. Later on, speed becomes more important but initially I tell my students that so long as they are plus 10 and minus 5 let it go. I also tell them that there is a minimum speed that they are not to go below at any time until over the fence.
The first part is getting them to understand what the glide path is and how to determine it. Then how to fly it.
If the airplane is above the glide path, put it back on. The easiest and fastest and most accurate way to do that is by using the elevator. If the diversion was small, the speed should not be much affected and will settle down once the glide path is re-established. No need to touch the throttle unless the average speed is not within the parameter established.
Keep the sight picture using elevator and the speed stays the same.
Later, I expect coordinated use of both controls but intially students find it difficult to do this and also intially they do not have the discipline to even be aware that they are off the glide path and do not appreciate how important it is to land at a nominated point on the runway. Good habits should be learned early. Landing accurately is an essential skill.
It is like parking your Toyota in the garage; you simply MUST do it right or you will hit the side or back walls. Landings should have the same discipline and this should be inculcated right from the beginning. I remember doing this in the Air Force and we were not allowed any variance from the standards. I believe it made me a better pilot.
All that you guys have given me is great stuff and reassures me that I am not so far off the well-trodden path.

[TheChitterneFlyer]

So... I'm correctly assuming that we're talking about 'student pilots' and not the experienced flyer i.e, that the runway is always in view and that it's not an instrument approach?

'Student Pilots' must adequately demonstrate their ability to safely recover from a stall condition; be it at a safe altitude or during the last 500 feet. In my view; and I don't necessarily subscribe to the syllabus; we must provide a common method for doing so. When the student has shown an appreciation of what is trying to be achieved; and only then; we can then allow the introduction of alternative methods of flightpath control.

I'm sure that you will agree, that the student's ability to fully understand the mechanics of flight requires a modicum of repetitave input. If you start swapping and changing the rules, at a much too early stage, you're going to end up with a confused pupil!

Give him/her the basics, but when the time is right... show them the alternatives! Food for thought...

TCF

[betpump5]

attitude for speed and thrust or power for glidepath

Ah yes, the third most discussed statement on aviation after:

1. Integrated or Mod for training?
2. What makes a plane fly? Newton or Bernoulli

It seems to me that your post is to have a go at the most basic lesson which is Attitude for Speed, Thrust for blah blah blah.

And I agree with you. In my 9 year career of questioning this, no one has ever been able to back up this principle with any answer worth listening to. And you are right, on an ILS if you use attitude for speed, then forget about making a good landing.

The taught concept goes against every single human instinct. If you are going too slow, then you increase power. Cessna 152 or a 744. No argument.

Its about time someone got rid of this ridiculous concept - unless they can come up with an excellent unquestionable reason as to why you would NOT increase power if you are going too slow.

[DFC]

When the student has shown an appreciation of what is trying to be achieved; and only then; we can then allow the introduction of alternative methods of flightpath control.

There is no "alternative method of flightpath control".

One controls the flight path by moving the elevator, ailerons, rudder and (for powered aircraft) using the throttle to vary the force along the thrust vector.

For the constant correct approach you need;

1. The flight path to be towards the aiming point or put another way, you need to be on a collision course with the aiming point and to hit it (like anything else) it must remain static in the window.

2. The angle between the flight path and the horizontal must be correct

3. The track over the ground must equal the runway centerline; and

4. The airspeed must be correct.

No matter how you think of it, how experienced or not, you can not complete a stable approach without the above.

So when you want to teach a person how to do number 1 above is it not very simple to say - use the controls to keep the aim point steady in the window?

Then one can remind them of the secondary effects that they covered some time earlier and remind them that then the flight path angle steepens gravity accelerates the aircraft along the flight path and vice versa so if they need to correct by using a different flight path then there will be a need for a thrust change so that speed remains constant.

I can explain - pitch up and increase thrust to conteract the secondary effect of reducing airspeed in 10 seconds and it has already been covered on exercise 4 as the primary and secondary effects of moving the elevator.

In exercise 4 the student will also have been shown the primary and secondary effects on increasing and decreasing the thrust settings.

I can also explain why one can think of it as increase thrust to change the flight path and adjust attitude to counteract the change in airspeed but it takes longer, doe snot relate to the previous lessons and is harder to relate to what one is trying to acheive.

In the end however, if a "point and power" pilot and an "power for height" pilot both fly the same aircraft along the same approach they will both manipulate the controls in the exact same way. The only difference is in the mind!

----------

The main reason why this issue rarely comes up until pilots start flying ILS approaches or something for which a constant approach angle is essential is that for PPL and CPLs in training, instructors simply require that the flight continues towards the aiming point at a constant speed.

Too often if the aircraft becomes a bit high, the answer is to fly a steeper flight path towards the aiming point with reduced thrust to offset the resultant increase in airspeed. If the aircraft is a bit low, the flight path is aning flown towards the aiming point but with higher thrust.................and people are thus dragged into the mindset of power for height.

In effect, PPL and CPL training do not concentrate on re-intercepting the correct approach angle and everything is based on travelling towards the aiming point.

When it comes to flying the ILS, then if the aircraft is not on the correct path, a new path must be flown that does not take the aircraft towards the aiming point (they may already be heading there) but to regain the correct glidepath.

Far too many PPLs and CPLs do not understand that travelling towards the aiming point is not all there is to flying the correct approach.

While every instructor will draw lovely intercept lines for getting back onto the centerline, very few do the same in a vertical sense whan talking about the appropriate approach angle.

Regards,

DFC

[Meikleour]

This is a perennial `chestnut`!

I have always assumed that the Attitude for Speed technique was introduced early on in pilot training because usually the training aircraft is single engined. Thus the forced landing scenario has to be taught early on. However what you advocate is exactly correct for almost all operations, the problem arises in how one weans the tyro pilot away from the early training. Incidently, John Farley`s book has some excellent views on this subject.

[boofhead]

I work with experienced pilots as well as tyros and both types have trouble at times. Generally pilots who are familiar with short fields find it easy to make a precision landing, but those who only fly C182 or the like have never learned how to do it. Students cannot handle two things at once and I am of the opinion that glide path control to a landing on the nominated spot is the most important part of learning to land. Using the elevator to establish and remain on the glide path seems to work.
I am grateful for the advice and information given to me here. I am relieved that I am not completely off the wall.

[DGAC]

Power for rate of descent and elevator for speed are used to ACHIEVE the correct glidepath. Once on the correct glidepath, power is used for speed and elevator is used to keep the touchdown point in a fixed position in the windscreen.

[chrisN]

I offer nothing about the arguments re powered aircraft, but the original poster was completely wrong to say “And a glider does not have power to adjust the glidepath (sure it has speed brake but I am sure most glider pilots do not pedal their way down final with that control).”

I don’t know why the word “pedal” was used, but for the record, glider airbrakes or spoilers are hand controls.

All gliding operations in the UK teach that you do indeed use the brakes continuously if necessary, to maintain glide path towards a reference point, in particular below 500 feet. It is often the case that they have to be reduced when descending through a wind gradient.

The elevator is used to maintain airspeed. With some gliders, a small change in elevator is required to maintain airspeed when the brakes are opened significantly more, but the essence is always elevator for airspeed, brakes for rate of descent.

Trying to point to where you want to go in a glider would lead to potential disaster in attempting a field landing with limited room for flare and ground run.

If you want to teach something else for power, or (worse, IMHO, teach different things at different stages of learning), feel free, and be aware that converting glider pilots to power you will need to explain why it is different, but please don’t propagate misleading advice to anyone learning gliding. There is standardised training of gliding instructors to a standardised syllabus in the UK, and we do what I have said, and not what Boof says..

Chris N.

[boofhead]

I stand corrected on the use of speedbrakes. Indeed that is the way I fly gliders on approach, but I thought I might be translating powered techniques onto the glider. A better example is a powered airplane on final, high and a little fast. Throttle is already at idle and flaps are full. Too late to sideslip.
Choices are to land long or land fast.
I maintain that one should land fast, maintaining the aiming point.
Of course it might be necessary to hold off in the flare until the speed and attitude are acceptable for touchdown, but changing the touch down point should not be acceptable.
There is only one control available and only one that needs to be used.
This is not meant to cover a gross error, when either a go around or a changed aiming point would be better.

[DFC]

The elevator is used to maintain airspeed. With some gliders, a small change in elevator is required to maintain airspeed when the brakes are opened significantly more, but the essence is always elevator for airspeed, brakes for rate of descent.

I think that you will find that the elevator varies the flight path i.e. if your current flight path is giving you 80Kt and you want 100Kt then you will use the elevator to steepen the flight path so that the airspeed reaches 100Kt.

If the elvator is used to make the flight path steeper then thanks to gravity a secondary effect is that the airspeed will increase.

The airspeed acheived in a glider is a result of how steeply the aircraft is descending along the flight path less the drag which is a function of both airspeed and configuration.

Trying to point to where you want to go in a glider would lead to potential disaster

Of course it would because in the absence of an engine, the only force available to provide "thrust" is gravity. However, if there was no variation in the wind, the constant point would remain that - constant and if the aircraft is clean and at the best glide speed then by definition there is no way to move the constant point forward. One can however move that point closer by steepening the flight path.

So again there is two ways of looking at the same actions;

Do you use elevator to steepen the flight path and add drag to prevent a speed increase or do you add drag and use the elevator to steepen the flight path in order to maintain speed?

When it comes to engine failures, I can confirm that people who use point and power as a mind set during powered flight unually perform far better.

Why? - simply because if you ask a person to use the controls to keep a point constant in the window then as an unavoidable consequence if they can do that task then they have to be able to recognise when the constant point is moving or no longer coincides with the place they wish to travel towards.

They usually understand that airspeed is as result of the thrust / drag balance coupled with the flight path and obviously in the absence of an engine all they have is gravity to provide "thrust".

Regards,

DFC

[TheChitterneFlyer]

Forgive my earlier posts on the subject, but it was my understanding that stalling was the consideration, and not flightpath control, i.e. increasing power rather than reducing the angle of attack?

I believe that we're all in agreement here; there's a difference between 'point and power' as opposed to 'power for ROD'. It is of course important to maintain the correct 'approach path'; albeit in a simple single engine or a heavy multi. The difference being, of course, is that if you're very high (in a simple single), and all you have is a visual reference, you cannot maintain the speed and increase the ROD (to the same aiming point)! Actually, in some of my experiences in a heavy B747, you can't do that either... unless you wish to prematurely hit the ground with idle power! The vital part is assessing whether or not it's 'do-able' within the distance remaining!

Actually, this is a great topic for discussion, but not in a closed forum; because all of us need to be adequately understood (and we're mostly missunderstood within this forum), which cannot be easily undertaken by typing words into a little box... I'll probably be berated for my short missives! However, keep your thoughts coming... they're ALL interesting, and, all have their merits.

TCF