STOL Tips

STOL Tips: Attitude flying

This first installment of The Approach -- a series on strategy for approaching and departing backcountry airstrips -- will cover final approach, and show how proper use of attitude flying can produce a stable landing with very little excess energy that could otherwise extend landing and rollout distance.

The following article, while written by a knowledgeable and experienced backcountry pilot, is not a substitute for actual instruction, and therefore should be considered only entertainment and possibly a talking point with your own certified flight instructor.

Having given quite a bit of backcountry instruction over the years, I’ve noticed that there’s a significant divide between the traditional approach taught in primary training, and what is commonly needed when doing precision approaches in the backcountry/bush flying environment. Before you worry about runway length, surface condition, bushwheels, type of plane, taildragger vs nosedragger, density altitude, and the general airstrip environment you need to be able to consistently hit your intended touchdown spot, plus or minus a few feet. None of the aforementioned factors really matter if you aren't able to consistently do that.

Convention vs practical necessity

Let us first examine the commonly taught conventional landing approach:

For the most part there are two schools of thought in the primary light aircraft instruction world, the first is based on: "can you make the airport in the event of an engine failure"? This stems from a risk management philosophy of flying, rooted in the fact that failures do happen, but nowadays far less often than when this philosophy originated. Modern engines enjoy a much better reliability record that in the early days of aviation when shaping procedures around emergency was important because failures were very common. For the CFI doing their bizzlionth lap around the pattern realizing that the statistics for them only get worse and worse with every passing instructional hour, they likely err on the side of maintaining a little extra energy to make the runway.

Despite being setup on a nice glide slope, this Cub pilot has a slight nose-down pitch attitude, and is carrying far too much energy (65 mph) at this point in the approach. The landing and rollout distance will exceed what many backcountry airstrips can provide. Continue reading to learn how to control angle of attack on the approach to minimize landing distance.

I certainly try to minimize my risk when in the pattern, however in the backcountry there often isn't a traditional pattern; sometimes the only acceptable spot to land for miles is your intended destination. If you're overly worried about your engine quitting when doing this type of flying you are certainly going to limit your available options for destinations. Everyone has a comfort level, and each person has to develop their own, but in the backcountry there are times when you are 100% relying on your engine, and often that is in the "pattern".

The second school of thought is really a hybrid of the conventional, combined with some arbitrary numbers. How many times have you heard "80 knots on downwind, 70 on base, and 60 over the fence increasing your flaps one notch per leg of the approach"? Presumably this is based on a similarly valid, but perhaps more applicable to primary training, concern. Fear of the low altitude stall/spin scenario is probably responsible for more runway overruns than wind and ice combined, due to its overreliance on abundant airspeed. While the stall/spin is a real concern, pilots looking to get into the backcountry should be at a skill level that has transcended this basic skill or lack thereof.

While working as a primary instructor in my teens, I can't express how much easier it was to just put a big margin of error between final approach speed and stall. Rather than a strict adherence to attitude control, I would just say: "Stay above 65 knots on final and we will bleed it off above the runway." That way I could be staring out the side window and texting my date for the night. To all my former students: sorry about that, but after all, we were working with a 4000' runway at sea level. Precision was not a focus but rather smooth safe touchdowns and crosswind competence. We also routinely used up 3000' in a Cessna 150. Unfortunately the law of primacy is strong and this lack of attitude/speed discipline is rooted in early training, and is pervasive in general aviation; I was certainly a big contributor to this for years.

A better way

It wasn't till I started flying turbines that I realized there was a much better and very common method for precision approaches. Combine that with a little training out of the autorotation chapter of the helicopter flying handbook and I had an epiphany: Jets ALWAYS fly "precision" approaches. Every approach is treated like what a "backcountry" precision approach should be. They fly ref speeds. These speeds are based on weight and some other variables, but essentially there's one constant: The Angle of Attack (AOA) Indicators on the jets always read exactly the same if you're flying your numbers correctly.

I'm sure I'm not the only one, but sometimes it is easier to just look at the AOA compared to relying on TOLD (Take Off and Landing Distance) cards and the associated Ref speeds. While in my world you can chalk that up to laziness, I understand the Navy has heavy reliance on the AOA indicator as a primary instrument, so maybe I was on to something; I have heard they land short.

Most small planes don't have an AOA indicator you say? True, but they do have a wing and a horizon that sufficiently replicates an AOA indicator. In fact it is bigger, easier to understand, and keeps your head outside the cockpit better than any panel instrument.

The poor man's angle-of-attack indicator: Bottom of the wing tip in relation to the horizon.

The basic concept is that you want to fly a stabilized approach with full flaps at a minimum airspeed sufficient to keep you away from stall but arrive at the predetermined spot with very little forward energy to dissipate once touched down. Simple, right? To make this happen you can use your wing and the horizon as a poor man's AOA indicator. Every airplane is different, but there is a certain attitude that can provide the right speed/safety margin for real short landing results.

For the sake of simplicity I'll use my Maule M7 as the example aircraft. I climbed up to a safe experimentation altitude and configured for what was basically a very low power setting and steep approach angle. I also stalled the airplane several times in this configuration to get an idea of my safety margin. After some practice I determined that a wing that is basically parallel with the horizon provided a very low speed (roughly 38 mph on my crappy airspeed indicator) and approximately 600' per minute decent. I burned this "flat wing" picture attitude into my brain and started paying attention to different loaded weights and what the resulting change was.

Essentially there is about a 9 MPH and 100 FPM range from "play" weight (light) to "full" weight. I never altered the wing angle to the horizon, just used power to adjust glide slope and break my decent rate right before a very quick flare. Over time I got used to this method and even started playing with my approaches and got really aggressive with stalling all the way down (a page straight out of Stick and Rudder).

To clarify, this is not "dragging" it in, a term that is often used to describe slow, high AOA, power-on approaches.

This method resulted in an extremely steep approach that involves managing pitch in a manner kind of like auto-rotating a helicopter. If I was overshooting, I'd pitch nose up and increase wing angle slightly, allowing me to descend very steeply. I was soon able to land straight into spots that, prior to using this method, I would manuever on final to avoid the the short final approach obstructions. While this is fairly advanced version of what I am advocating, it does demonstrate that, given a machine that one is very comfortable flying, there can be found a very slow approach speed and steep angle with ample safety margin. It's all about paying attention to AOA.

Putting knowledge into practice

I'll walk you through the steps as I would teach it to student (most of mine are fairly high time pilots and own a capable backcountry machine.) I should point out that we teach our stuff at public or private dirt strips and private property, not actual backcountry strips. We do this to alleviate some of the pressure that many of our favorite backcountry airstrips are under. If you're camping or hiking near a strip enjoying the remote solitude, the last thing you want to endure is a plane doing repeated squirrelly touch and goes. Additionally, for the pilot, there is enough new material being introduced in a lesson, that that last thing one needs is the stress of hugging a canyon wall while staring at a mountain on short final. It's best to focus on a new skill in a simpler environment.

For simplicity's sake we'll use traditional language for the pattern. However, in the backcountry there is very often no such thing as an orthodox downwind or base leg, but rather a downstream arrival or cheating in behind some trees on the lee side of a ridge line. We'll cover that strategy to the approach in a future installment about evaluating the site.

What's your plan here? The backcountry airport environment often doesn't provide the opportunity for conventional pattern to be flown, and might require a unique strategy for approach. More on that in a future installment.Photo: Allen Macbean

The key is to stabilize early on, be slow at a fair distance out from the strip, and enjoy the scenery; slow down to at least middle of the white arc on your airspeed indicator by the time you enter the "pattern," or in this case the "airstrip environment." I'm quoting these terms because we're projecting conventional square pattern approach terminology onto a scenario that may not always accomodate it.

By "midfield" have some flaps in and get ready to pull them all in at the point of decent. In the pattern this is basically abeam the "numbers" on downwind. At this point you should have your predetermined wing angle established and set (basically parallel with the horizon, airplane dependent.) In the case of a lot of backcountry-type planes you may not have enough pitch-up elevator trim once slowed, so you're going to have to muscle it.

With the wing angle set, you now just drive the airplane down the glideslope with power, never changing that wing angle. This will allow the most stable approach you can accomplish. It is quite literally the most often said, but rarely practiced part, of light aircraft instruction: "Pitch for airspeed, Power for altitude," but at this point, we're going to truly focus on that concept as a pure necessity for this kind of approach.

This Maule M7 is on a short, steep final approach, but notice that the nose is not pointed down. The wing chord, and the pitch attitude, are fairly flat, producing a stable, controlled sinking approach.

Most people I've taught initially had a tendency to drop the nose in the turn. Try to fight this urge. Just keep the same wing angle; if you don't increase the load on the wing, you don't have to worry about the dreaded stall/spin. Remember, you're in a descent, so you can keep the turn at 1g by giving up a little altitude. Holding the wing angle at its predetermined spot, you now just adjust power to stay on glideslope. As you approach your touchdown spot you won't need a "round out," as you would with an excessively large margin of airspeed, but rather a quick flare, probably with a shot of power depending on the steepness of the approach and the descent rate. I won't go into the finer parts of touchdown as those very greatly with different airplanes.

A few points to remember:

  • The steeper the approach, the safer.
  • Use the same wing angle regardless of weight; less power equals steeper glideslope.
  • The steeper the approach, the more you will need power in the flare.
  • The airplane will need to be balanced on the aft side of the envelope to make the flare easier or even possible.

The flare attitude-- good for dissipating energy just before landing, but too much AOA and too little visibility over the nose for a useful, stable approach.

This takes practice, lots of practice, and usually a lot of overshooting the touchdown spot occurs, as most people aren't comfortable being that steep and they start to dive for the runway reducing the wing angle and increasing the efficiency of the wing by reducing the induced drag. This betrays the whole concept, and makes it difficult to get back on glideslope; it is simply no longer available as your collective energy has been increased to the point where reducing power isn't enough to get slowed down.

To the same point, if you were to lose your engine, there is some recourse. You can extend your glide by lowering the nose; it's like retracting the spoilers on a glider, you gain efficiency quickly. If you started the approach steep enough, you might even be able to make the landing zone if you get the nose down fast enough, hence the steeper the safer (not to mention it allows you to cheat all kinds of obstacles).

Analysis

Let's examine what is going on and why this method works for us, and why I have found it easiest to teach.

By using a steep glide slope, you're really using gravity as the primary source of energy as opposed to using the engine. A lot of the collective energy is vertical, which you dissipate in the flare. To clarify, this isn't "dragging" it in, a term that is often used to describe slow, high AOA, power-on approaches. I am uncomfortable dragging it in for a couple of reasons: First, it is relying on the engine heavily. Second, it makes it very hard to see were you're going, as the nose is pitched up. Third, it exacerbates all the P-factor issues. Fourth, it makes your collective energy more horizontal than vertical because you are already in flare attitude without being able to dissipate energy in the actual flare. Your only option is to pull the power off, which at such a high AOA and low airspeed, could result in a poorly timed stall.

A high pitch attitude, as observed by the relative angle of the wing surface to the horizon.

Going with a "flat" wing and steep approach, you are really pushing the air over your wings with gravity, using your engine only to make minor if not frequent adjustments to your glide slope. You can see much better, and you aren't creating a bunch of torque while crawling your way to the touchdown spot. The true "flat" wing is slightly different in every plane, for instance in my Carbon Cub it is a little aft of parallel with the horizon, with our PA-18 Super Cub being even a little more aft. The Cessna 185 seem to be about the same as the Maule M7 series and late model Huskies. One thing I have learned is it is very hard to stall a plane while in these attitudes as long as you are in a descent.

A low pitch angle, as observed from the wing to horizon relationship. The nose is pitched downward.

How is this different than what is commonly accepted a light aircraft approach? If you look at your wing during an approach without having done this type of flying, you will most likely notice a slight down angle of the wing to horizon. Inevitably during the landing, you'll transition the wing from that down angle to slightly up angle during the flare. That basically amounts to a "round-out" or "bleeding it off" over the runway and then the flare. This burns up valuable horizontal distance, and takes extremely good timing to hit your point. Surely there are folks out there that can do this, but it certainly takes Bob Hoover type energy management to be consistent. Even if you can time it right you've still used a shallow glide slope for the last part, meaning your obstacle clearance compromised.

With a flat wing approach you arrive at just a slightly lower AOA than flare attitude, allowing that energy to be dissipated in the flare, touching down at the slowest possible speed, which allows for the shortest ground roll.

There are many ways to skin a cat and surely this is just one of them, but it is the method that we use for safe consistent results in the backcountry. There certainly times when we use other methods but this one is the method I am most comfortable with most of the time.

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Patrick Romano

Flying since the age of 14, and an instructor by age 18, Patrick Romano has packed over 8,000 hours of experience into his career, having commercial certificates and ratings in nearly everything save for light-than-air. As a backcountry flying instructor in the Boulder, Colorado area, he manages about 400 hours per year in his Maule M7 and a variety of other bush planes.

Website: backcountryaviation.com

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