Final approach conundrum (stable versus safe)

[ScottOHare]

I typically fly my DA40 NG in the pattern as follows: Abeam the numbers, flaps to approach, power to 25%, pitch for 90 kts. Turn to base, slow to 85 kts. Turn to final, if at or above glide slope, flaps to landing, pitch for 80 kts. I find with full flaps 25% power isn't enough to stay on the glide slope, typically need 35% power or so. Slow to 76 kts over the numbers and power to idle or maybe a little more since the prop acts as a speed brake at idle.

Would prefer to reduce power one time and not increase it so still experimenting with it.

[DaveS1900]

Greg,
Your entire flight has various levels of risk and in some cases a lot more risk. The departure leg - climbing out, low and slow is possibly the most exposure you have to danger. Or flying cross country out of gliding distance from an airport, especially at night.

Also, a common reason for engine loss near the landing airport is from fuel starvation.

Be safe, mitigate your risk as best you can. Always be searching for a place to put the airplane down if you lose the engine. But, don't go crazy and fly a final that is way off from the POH targets, and possibly at the edge of your abilities.
Never dive for the runway -- pitch for airspeed; power for descent angle.

Dave S.
Ohio

[Boatguy]

I agree that flying the fully stabilized approach (which requires some power) "feels" the most professional. But I can't deny that I feel safer when I know my plane has sufficient energy to make the runway even if the engine goes kaput.

There is a lot of talk about being low and slow leading to a stall spin in the pattern so I can appreciate your concern. But it is the rare accident report where the accident was caused by engine failure on downwind/base/final. The stall/spin scenario is usually encountered when a pilot overshoots the turn to final, banks hard and then uses too much rudder attempting to further tighten the turn, putting the plane into a skid. The bank over 30˚ raises the stall speed, and the skid ensures the now very low inside wing will stall first which causes the unrecoverable spin.

Ironically, one of the causes of overshooting the turn to final is flying too fast because the higher speed significantly increases the turn radius. Flying fast in the pattern is most likely raising your risk level. If you overshoot the turn to final, either gently get yourself back into alignment with the runway, or just go around. Don't try to save it.

About six months ago I spent a couple of hours in the pattern with a CFI, pulling the power to 0% on the downwind at the numbers and trying to land on the numbers; even with LDG flaps I landed very long the first few times! Next I found myself turning base early, and then having to overshoot final and essentially circle back to the runway. Eventually I learned to be patient and fly just a slightly shorter downwind in order to land on the numbers with no power. I suggest that if you go up with a CFI and practice this for a couple of hours your concern will be dramatically reduced.

The reality and the statistics, as Greg wrote, show that TO and departure, when you are at 100% power in an NG, is much more likely to be where you'll have an engine failure and have few choices on where to go. Once you're on the downwind leg the engine is under very little load.

Something else to keep in mind is that the POH speeds are for final; you can certainly fly the base at 80-85KIAS. The DA40 is very sensitive to those speeds, which are in turn very sensitive to weight. If you are fast over the fence it will float forever. You'll find landing much easier if you are on the POH speeds over the fence.

You can also consider landing with TO flaps (speeds are +2 over LDG flaps). I know DA40 owners who always land with TO flaps and I probably land with TO flaps about half the time. As someone else wrote, after you turn final, pitch for the POH speed and use the throttle to adjust the sink rate. In an NG with TO flaps you'll be at about 15-20%. You'll have a very stable approach with no stall/spin risk.

[pietromarx]

I once did some instruction with a guy who had a glider license, as he was going to add a SEL. There are significant differences between sailplanes and, say a DA40. The dude had some habits and expectations that needed correction.

- Sailplanes are typically landed level - not a good idea in a tricycle-gear plane.
- They have spoilers to "stick" the landing.
- Sailplanes can have breathtakingly wonderful glide ratios - even beyond 50:1

The good thing is you learn to really nail your airspeed and get real about rudder usage.

Getting a glider rating and some time in one is definitely cool, but there are some things that are unrealistic to try to apply to the typical powered lightplane.

While these statements are accurate, they're misleading. We were discussing the approach phase, not the flare. There is no difference between the approaches in any type of airplane and one uses flaps and spoilers to get the angles one desires. You can retract or extend an airbrake / spoiler to flatten or steepen the descent (a bit) in the same way as pushing the throttle forward.

Might also do to remember that Diamond started as a sailplane manufacturer and those long wings do require a bit of stick and rudder, as well as avoiding a lot of float, both of which are endemic to the DA-40s (and -20s and and...)

Really suggest learning to fly gliders (and taildraggers). It will make you into a better pilot in every way.

[gcampbe2]

Lots of great advice in this thread. My thanks to all of you for taking the time to share your expertise.

Russ: Ya, I am well aware of the classic late base to final turn resulting in a stall/spin when pilots try to salvage the approach by increasing the loading on the wings when low and slow. I'm an avid listener to Max Trescott's Aviation News Talk podcast (very worth checking out if you haven't heard it: https://aviationnewstalk.com). Max has done multiple episodes on this topic, and it seems that at least once a month he gives details of a fatal GA crash caused by a stall/spin on the base to final turn. Sage advice to just go around if you’re late on the turn!

I also will be booking some time with an instructor to perform some power off landings to fully appreciate the aircraft’s capabilities at different stages of the circuit. Of course, whether you've got a headwind or tailwind on base will likely make a huge difference on one's ability to make the field and the dynamics of a given power off approach. But I think this is “must have” experience, and as soon as I get my DA40NG back (currently grounded for the fuel pump gear repair) and get a few flights in the bang the rust off, I’ll book some time with my instructor. Heck, the best way to answer my own concern about making the field is to actually (safely) explore trying to make the field without engine power.

I curious how many other DA40NG pilots also make a habit to land with TO flaps? Coming from a C172, I used to regularly land with 20 degrees of flaps rather then the full 30 (or even 40 degrees on some models!). I did find at 20 degrees I had a more stable approach, handled the crosswind better, but did have to have the airspeed perfect or I’d float along down the runway. Time to do some experimenting in the DA40NG with TO flap landings.

Getting a glider license has also been something on my list, and the concept of every approach being a forced approach can only make one a better pilot. I am the first to admit that as a low time pilot my hand and feet skills, in particular my feet skills, can be improved. The problem is I’ve been having too much fun with my DA40NG to make the time for glider training

I also hadn’t considered that the probability of engine failure is correlated to the engine load. This makes sense, and would imply that the base and final legs of the approach are less likely to be impacted by power loss than takeoff, provided fuel starvation is not a factor.

Once again, my thanks to all you more experienced pilots taking the time to pass along your knowledge!

[Boatguy]

I'm an avid listener to Max Trescott's Aviation News Talk podcast (very worth checking out if you haven't heard it: https://aviationnewstalk.com).

Me too!

[CFIDave]

Rather than trying to fly airspeed on approach, I usually teach use of a consistent power setting. On a DA40NG, I teach use of 20% power (load) for both instrument approaches and when flying the pattern (circuits):

1. For instrument approaches with vertical guidance (i.e., ILS or WAAS GPS LPV), a 20% power setting with T/O flaps flying a typical 3% glide slope will result in a consistent 90 KIAS. Once you "have the field made" on short final, add full flaps, drop the nose slightly, and start taking power out until you're about 75 KIAS over the threshold.

2. For flying traffic patterns, pull the power back to 20% when you're on downwind abeam the numbers, add T/O flaps, and begin your descent. If you judge your path properly, you won't need to touch the power again until you're on short final -- when you also add full flaps, drop the nose slightly, and start taking power out until you're about 75 KIAS over the threshold.

This same technique works the same for a DA62 or Austro DA42 NG/-VI, except you set power to 35% instead of 20%.

[Rich]

I have an illustration where being able to go beyond cookie-cutter approaches one finds in various publications and presentations has real value. It was a flight from Prineville (S39) to Sisters (6K5) OR I made today.

The approach to RWY 20 at Sisters requires coming in over a 100+ (ridge + trees) obstruction about 500 ft. from the threshold. Unless you intend to trim the top of one of those those trees, we're talking ~4:1 descent path. That's 14 degrees. Full flaps, 70KIAS over the trees, slowing to about 63 over the threshold. Then rotate, compensating for the fact the runway is neither level nor flat. It does have very nice new pavement, though, and adequate width. About 2200 ft. shorter than my home field. There is no turnoff - you go all the way to the end. I needed power in the taxi to do that.

The return trip required fitting between two other aircraft (C-172s) doing practice patterns. (We had a 3-way conversation going to negotiate.) They were flying kind of wide patterns, nothing too outrageous. Ad-libbing on my part was called for, as my speed in the pattern needed to be adjusted based on the guy ahead. When I get in this situation it's my habit to stay high on the turn to final to hedge against a possible go-around. Then when it's obvious the plane ahead won't be an obstruction, start on down as steep as it takes. Not as steep as the first landing but probably 6 degrees or so. Same over-the-TH speed. Easily made the first turnoff.

Because I pretty much always use full flaps and these speeds on final these latter-stage approaches were no big deal. The only real variation is how steep they need to be. Regardless what one might think they are stabilized, because the plane is doing exactly what I intend.

[TimS]

The concept of stabilized approach is based on a straight in approach, and mostly deals with IFR approaches. It really does not apply flying in the pattern.
As for the pattern, make sure you fly the recommended distance. This is much closer to the airport than most people fly.

Before picking a side on the debate of stabilized approach, understand why it is critical to airline operations and aircraft, and if those considerations are import or even good for a piston plane (start by looking at power to lift, spoilers, reverse thrust, and braking options).

Tim