Attitude for Airspeed & Power for Rate of Descent?

Attitude for airspeed and power for rate of descent in the approach phase of flight is the methodology of choice for most flight training organisations involved in elementary pilot training (and if you’re a student it’s probably what you’re learning right now) – but is it correct? The short answer is yes, and the long answer… well, kind of remains yes, but that doesn’t mean that there’s possibly a more effective and universal technique that we can apply.

There’s a growing fraternity of pilots that insist upon teaching ‘attitude for profile and power for airspeed’ (as opposed to ‘attitude for airspeed and power for rate of descent’) – so this short post is about addressing my experience with the two methods. Keep in mind that I remain open to both instructional techniques and I’m still yet to completely favour one over the other in early training. I’ll generally file various techniques away – whatever they happen to be – and introduce variances from published SOP’s when I see a student struggle with a particular concept.

This blog details the technique flown during an approach to land with a very general comparison between light aircraft and larger jet or turbine types. It is intended for elementary pilots and instructors with enough guff to illicit some thought. It should be noted that I’ve exaggerated the argument to hopefully inspire some discussion.

The Two Techniques

When you’re undertaking your elementary flight training, you’re likely going to be taught attitude for airspeed and power for ROD… then when you start your instrument rating you’re likely going to fly power for airspeed, attitude for ROD (or flight path/profile). If you undertake an instructor rating, you’re going to be taught a combination of the above and also introduced to ‘Point & Power’ (gun-barrel or ballistic) approach, the ‘constant angle variable speed approach’ and the ‘point of no relative movement’ approach (among others). At the end of the day, they’re all a function of “Power + Attitude = Performance”, and all methods essentially accomplish the same task.

Power for Airspeed. Attitude for Profile (aiming point)

Put any non-pilot in a flight simulator and they’ll almost always fly an accurate approach if you have them fly attitude for profile. Why? Picking a point on the runway and simply flying towards it is intuitive and very natural. It’s not uncommon to see schools that apply variants of this technique use a marker pen to draw a cross on the windscreen that corresponds to the aiming point on the runway. Maintaining the windscreen mark over the top of the threshold through your field of vision will ensure the flight path of the aircraft to the aiming point on the runway. The question as to why this particular technique isn’t considered best practice is a little puzzling to those that teach it.

Attitude for Airspeed. Power for Rate of Descent

In essence, if a pilot is high on an approach, he or she will reduce power that will in turn reduce airspeed. Since we maintain a constant IAS on approach, lowering the nose will maintain our desired airspeed… thus increasing the rate of descent. The opposite applies when the aircraft is low on approach.

The technique is based on constant airspeeds with defined attitudes/configurations.

Introduction

In elementary training, instructors generally keep to ‘attitude for airspeed and power for rate of descent’ for a few reasons – none more important than the fact it seems to work. The technique is historically rooted in approaches that were taught in very low powered aircraft such as a Tigermoth that often used idle thrust for the approach to land (and what little thrust was available in these high drag types wasn’t overly effective at approach speeds). Attitude became the primary method of controlling airspeed with a combination of s-turns and slips used to control the rate of descent. The attitude for airspeed technique propagated its way around training circles and likely remains the technique of choice for no other reason than the global resistance to any kind of change in the training end of the aviation market – even if it isn’t the most appropriate method. ‘Modern’ day syllabuses often haven’t been changes in over 60 years.

The attitude for airspeed approach might be considered an easy technique to apply since it offers the student continuity in methodology. From the first lesson you’re shown and told that pitching the nose up reduces airspeed, and you’re taught that lowering the nose will increase airspeed – and it’s a practical application that repeats itself through most phases of early flight. It’s a simple submission that tends to sit well with most students because they can see it work – and it does work… but we’re applying the secondary effects of controls to fly a speed profile.

Power for Rate of Descent

If you’re flying a small training aircraft and apply thrust, the aircraft often tends to pitch its nose up with a secondary reduction in airspeed… while reducing thrust usually has the opposite effect (an effect not likely felt in larger aircraft due mainly to the intentional coupling of the centre of gravity and centre of pressure). What does this mean in light aircraft? It means that when a pilot uses power to control airspeed in a light aircraft, they will inevitably have to make an attitude adjustment anyhow – so why not use this coupling effect to our advantage? The actual design and behaviour of most light aircraft seems to favour this technique.

If we’re high, we reduce power (primary effect: airspeed reduction) and the aircraft will pre-empt our next move with a secondary effect – the nose will pitch down to maintain airspeed. So, in essence, when flying an approach to land, reducing the power will increase the rate of descent without any actual manipulation of the controls. You might argue that it is the attitude of the aircraft that dictates the flight path, and you might be correct. Again, I’m referencing a secondary effect.

Light aircraft have slipstream over the tail and lift-producing inboard sections of the wing; meaning that thrust is directly related to (a small portion of) lift production. Reducing thrust doesn’t just slow you down, it decreases the coefficient of lift before airspeed even plays its part.

Both of these elements – the secondary effect of thrust reduction and slipstream – tend to support “power for rate of descent” as a practical and workable solution for student pilots. One friend I have belittles this technique by likening the throttle to the ‘up and down’ collective on a helicopter.

Attitude for Airspeed

Lower inertia light aircraft are often underpowered and flown very close (in terms of speed margin) to the tail end of the drag curve during an approach (notably, a short field approach). This is often the result of poor speed management due to the (arguably questionable?) technique of flying a landing speed as your approach speed). If your airspeed reduces on final below the point of minimum drag, additional thrust in isolation may be insufficient to increase airspeed. However, lowering the nose generally has an immediate and noticeable effect.

If you’re going to teach somebody to lower the nose on final to maintain airspeed as the sequence requires, you want to make sure there’s thrust there at the same time (to arrest the rate of inevitable descent). “Power for profile” tends to ignore the potential for an approach on the back of the drag curve with insufficient power to overcome the decay of speed and the likely high rate of descent. The ‘attitude for airspeed’ approach is almost like a safeguard for low time pilots who don’t have sufficient knowledge or skill to properly pick and choose and then apply a broader range of techniques most fitting to varying circumstances. Attitude for airspeed is a simple proposition that simply works.

The Drag Curve

Image: In the “region of reverse command”, or unhappy (and unstable) end of the drag curve (shaded in yellow), a decrease in airspeed translates to an increase in drag (the opposite of what you would expect forward of the point of minimum drag). With limited height to stabilise an approach, power in isolation may not be sufficient to overcome the drag if airspeed is very low.

Keep in mind that we have to teach a method that is ‘safest’ in the early stages of solo flight in the circuit. If a pilot is very low and slow in a training aircraft and they pitch the nose up to maintain profile, what comes next? Teaching power as a primary method to maintain profile might be considered an insurance policy against inexperience or a stall. Pilots will adopt more technically correct methods later on when their proficiency and skill permit it or when the aircraft type demands it.

Constant Angle Variable Speed Approach

The Constant Angle Variable Speed Approach is progressively being adopted by many flying schools. The approach is designed around an Attitude Reference Point (or ARP) for profile while power remains at a near-constant on a higher-than-normal approach path. At about 500 feet, the aircraft is slowed down progressively with application of flap (with a constant aiming point). The drag of the flap will slow the aeroplane to the correct threshold speed whilst the flap’s ‘lift augmentation’ will offset the loss of lift associated with the reducing airspeed.

The approach works on the basis that the threshold speed (or, generally, 1.3 x Vs) is the only speed that is required from the aircraft. Little regard is given to vertical speed or defined stabilised attitude/speed criteria. Although power and flap is effectively ‘set’ for the approach based on all the variances, it’s adjusted as necessary not for rate of descent – but to set a new aiming point on the runway.

This particular method can become a little messy with a strong headwind. It initially requires the ARP (your aiming point) to be advanced further down the runway, and the pilot will progressively let is drift back to the threshold in time for the flare.

Jet Performance

In larger types, a small change in attitude translates to a huge change in VNAV (vertical) performance. In some bigger aircraft, raising the nose by just one or two degrees will give you an immediate and substantial rate of climb (or descent) whereas it’s unlikely to have the same effect in lighter types (Rule of thumb: 1 degree of pitch change equals a change in vertical speed of approximately 2% of the airspeed). Attitude for airspeed is somewhat of an absurd technique in anything larger than a big single engine machine.

Instrument Flying

From an instrument flying perspective, power for airspeed and attitude for profile (or rate of descent) is virtually the only method that applies (and logically) works on an ILS, RNAV (GPS), VNAV (VOR) or similar approach since we’re flying a strict vertical path. It’s normal to set an approach power setting and then fly the glidepath by adjusting your rate-of-descent with attitude alone, and airspeed is unlikely to substantially affected. Should you need to target a particular airspeed, you will achieve this with the use of power. Subtle changes in attitude alone makes it far easier to fly a stable approach.

In any aircraft of any size fitted with a Flight Director (FD), the course bars will command changes in pitch and not airspeed. The ILS glideslope essentially does the same thing.

In most twins, and particularly turbine or jet aircraft, trying to fly a visual circuit with the use of power is virtually impossible. You must pitch the nose up or down to effect a rate of change to maintain your visual approach profile and power is used as necessary to maintain airspeed. In a light aircraft, however, we have a very narrow range of speeds, a slow cruising speed and low inertia… so power is actually quite effective.

What method is easier?

In my experience I’ve personally found that teaching somebody to fly an approach using attitude for airspeed isn’t quite as effective as simply teaching them to fly a vertical profile with attitude. Teaching attitude for airspeed requires a relatively complex set of cause-and-effect instructions to trigger requiring coordinated control inputs to maintain the new profile. Using attitude for flight path is more sympathetic to struggling students flying high or low on the approach; meaning that if they’re high or low they can simply adjust the aircraft attitude so their aiming point remains in a constant position in the windscreen. Power is then simply used to maintain the approach speed. Most trainee pilots drive a car so the simple idea that power increases your airspeed is easily applied.

Mixing Techniques

There are some organisations – particularly some military schools – that teach a combination of techniques; power for rate of descent on base but then reverting to attitude for aiming point on final. Personally, I don’t see any sense in intentionally mixing the two techniques during the ab-initio stages of flight training. I’m personally more of an advocate for a consistent and rationalised technique throughout all phases of the approach.

Feedback

I originally posted an abbreviated version of this post on another website (it was quickly re-written with elementary students in mind for FlyingTraining.net). Here are some interesting responses.

Peter, an Emirates 777 pilot, posted the following:

Real aviators landed airplanes on ships by flying alpha (angle of attack) and varying power to control the sink rate. Pilots of the blue persuasion insisted on landing on long runways by using power to control airspeed and attitude to control the sink rate. I like the navy way!

John Bartels (of QF30 fame ), and now an A380 Captain, said:

The RAAF teaches power for speed, and attitude for glide path. It’s easy to understand, works, and it’s accurate. And it then translates to every other aircraft type that they use, so you don’t have to learn another method.

The navy actually flies both an AoA approach, and an airspeed controlled by power approach. Flying alpha in something like an A4 was difficult to learn and hard to do accurately, but it allowed pilots to fly way down on the back of the drag curve… well below where any sensible person would want to be flying. It allowed you to arrive on the ship with the minimum energy… an absolute necessity. On shore bases it’s used for practice, but if you want to make air force style smooth landings, then you needed to be a bit faster, and so use the other method.

JB’s early flying experience was gained in Skyhawks and other fast navy jets in an environment that required aircraft be flown in a particular manner. However interesting, I’m not quite sure the technique applies to training aircraft!

In typical JB style, he gives us another point of view validating the military-style ‘attitude for profile’ method:

Also from the A4G. Put 170 mills on the gunsight (just a setting, don’t worry about it). Hold the cross hairs (pipper) on the end of the runway, and don’t let it move. Control speed by varying the drag (gear, flaps, speedbrakes). Approach IAS… around 200-220 kts. Start flare at 400 feet AGL.

An interesting technique not many of us will have the chance to fly!

Andy writes a very informed comment; part of which is reproduced below:

Pilots who use power for glidepath (or rate of descent) control typically don’t give a darn about their attitude. The idea is to trim the airplane for a certain airspeed and then don’t touch the elevator. Once the magical trim setting is achieved, just adjust power to maintain the proper glidepath. In my mind, the formula for this way of flying is ELEVATOR TRIM + POWER = PERFORMANCE. A pilot who flies like this doesn’t care if the nose is pitched down 3 degrees or 5 degrees or 1 degree. All that matters is that the airspeed is on target and that the airplane is maintaining its glidepath. Nowhere in this approach methodology does attitude come into the picture.

This comment opens up a can of worms we’ll talk about another time. I can’t agree that ‘attitude for airspeed’ pilots don’t fly with reference to attitude. I would often completely cover up instruments and have students fly an aircraft by attitude, engine noise and feel – completely void of any internal cues. Surprisingly, doing this would often result in the most accurate approaches. The same visual flying is far harder to accomplish when flying a ‘profile for aiming point’.

Conclusion

I believe that anybody wanting a career in aviation should apply the ‘power for airspeed’ principle simply because it’s the modus operandi most widely applied in the aircraft they’ll end up flying. There’s no use learning one method only to invariably adopt another method later on.

Flying schools will generally adopt a method and training technique that is most appropriate to the type of student. Even when I was forced to teach one method by a flying school training manual, I often reverted back to another when necessary to give the student another point of view. Seeing the same approach flown from another perspective was often enough to give the trainee pilot a better appreciation of the approach and made it easier for them to adopt either technique.

We’ll discuss each approach technique in fine detail over forthcoming posts. If you have suggestions and/or contributions to the discussion, please let us know.

Every method has it good and bad points. Simply put, pilot training should be personalised so that the most appropriate technique is taught from day one. Regardless of what method is used, one universal truth prevails: Power + Attitude = Performance.

What do you fly?

So, if you’re an instructor, what method do you teach, and why? If you’re a student, what were you taught? Did you find any aspect of your circuit training challenging? Were you introduced to multiple techniques? Please leave a comment and let us know.

Shortt URL for this post:

Leave a Reply

Your email address will not be published. Required fields are marked *