Final approach conundrum (stable versus safe)

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gcampbe2
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Final approach conundrum (stable versus safe)

Post by gcampbe2 »

I’m hoping one of you can help with a question that’s bothered me for a while as I’ve tried to increase my proficiency as a new pilot flying a DA40NG. The question is generic enough to apply to any airplane.

It seems to me that there are two competing goals when it comes to flying a standard approach:

1) Maintain sufficient energy to make the runway at all times in the circuit.
2) Fly a stable final approach (both airspeed and glide slope).

My experience has been that if I focus on the first of these goals, maintaining sufficient energy to make the field in an engine out scenario, I am required to make a quite high approach with an airspeed up around 85 KTS, delaying full flaps and deceleration to my 76 KTS final approach speed until quite late. I then essentially chop and drop the aircraft once I put in full flaps. With this technique I have minimized the time I am low and slow, and feel I can always make the field, even in an engine out scenario. But, my approach is only really stabilized for, at best, the last 20 seconds at best after I’ve dumped in the flaps, stabilized the airspeed at 76 KTS, and am on my (steep) glide path.

On the other hand, if I focus on a nice prolonged stable approach, I really need to have the aircraft at 76 KTS and configured to land further out on final with full flaps. I can fly this approach very stable, but I require a fair amount of engine power (or a lot of altitude) to complete the approach. On this style of approach at 76 KTS with full flaps were I to lose engine power I won’t have sufficient energy to make the field.

While I feel safer with the chop and drop approach, I recognize that the dynamic nature of this approach is not optimal particularly as I transition into an instrument rating, which will require very consistent approaches to be flown. How do more experienced pilots balance these two (seemingly) competing goals? Or, I have I missed something more fundamental here?

Thanks for the advice!
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Re: Final approach conundrum (stable versus safe)

Post by DaveS1900 »

Greg,
You will get several pages of comments and techniques, and all will be different.
My comments - 1) Use your POH. Read it first and take away what airspeeds and configuration you should target in the pattern and especially on final. Pitch for Airspeed and adjust power for the descent angle. You shouldn't be "diving" for the runway with a high airspeed.

The FAA recommends that you are straight in, on final, configured for landing, with only small adjustments below 500' AGL.

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Re: Final approach conundrum (stable versus safe)

Post by Boatguy »

gcampbe2 wrote: Fri Oct 08, 2021 1:27 pm It seems to me that there are two competing goals when it comes to flying a standard approach:

1) Maintain sufficient energy to make the runway at all times in the circuit.
2) Fly a stable final approach (both airspeed and glide slope).
To clarify, when you say "approach", do you mean an instrument approach, or flying a traffic pattern? The former are usually pretty close to straight in from the FAF about 5nm from touchdown, while the pattern has the base about 1nm out.
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Rich
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Re: Final approach conundrum (stable versus safe)

Post by Rich »

On an instrument glideslope, you can pretty much forget about making the runway on power failure unless you're on really short final. Glideslopes are set up at about 3 degrees. A 10:1 glide ratio is 6 degrees. Flaps and gear down? No way.

On the other hand some IAPs have really high MDA's - 1000 ft AGL or more. So from that point one has a free-reign for descent angle.

The term "stabilized approach" is a nebulous term anyway. I feel like any approach where the plane is doing what I need it to do is sufficiently stabilized. Have you seen skydiving planes coming back for the next load? The only trick about coming in steep is it makes proper flaring trickier.

I vary my over-the-fence speed depending on things like runway length, where the turnoffs are, other traffic, etc. Sometimes on instrument approaches I'll deploy all flaps at DH. But I have thousands of landings in N40XE and have a really good feel for what works. In heavier, slicker, retractable-gear planes flying by the numbers is more important.
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Rich
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Re: Final approach conundrum (stable versus safe)

Post by Rich »

One thing (not the only one, of course) you want to avoid is forcing the plane on when it's going too fast. I frequently visit the FAA incident page and it seems no day goes by where one or more planes run off the end or the edge of the runway. All kinds of types, including Diamonds. It's sort of on the wheels, maybe. (I suspect in some of these there is still more than idle power being carried.) But braking and nosewheel steering are nonexistent. The pilot has become a passenger, mentally transitioning to ground mode, but the plane has not.
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Re: Final approach conundrum (stable versus safe)

Post by gcampbe2 »

Thanks for the replies thus far. I am primarily focussed on a normal traffic patter approach, as opposed to an instrument approach. It makes sense to me that, on an instrument approach, one really has little choice but to let go of the idea of being able to glide to the runway at all points of the approach, since you are forced onto a specific glideslope. But on a standard VFR circuit, one has many options for what is "best".

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.
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Re: Final approach conundrum (stable versus safe)

Post by pietromarx »

gcampbe2 wrote: Fri Oct 08, 2021 5:45 pm 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 an energy indicator (the "turtle") on the G1000 that indicates where the plane is going at all times. To my mind a stabilized approach is when the "turtle" is kept on the runway numbers or approach end regardless of wind, power setting, etc. There is such a low likelihood of engine failure during the few moments of an approach as to be insignificant ... but there is always much joy in making the perfect landing with the engine at idle (call me a perfectionist).

If you have the time and inclination, my suggestion is this: go take some glider lessons. They say that glider pilots always make their landings and getting a glider rating will do several things for you:

1. Every landing you make will be perfect. Promise.
2. You'll know what to do with your feet (stick and rudder skills).
3. The engine will seem like the unnecessary crutch it actually is when flying.

As Rich says, an instrument approach may or may not put you into a position to do a power-off landing. This said, it is unlikely you would ever need to. There is so much more joy at being able to "nail" every landing regardless of winds, power settings, etc. when you have the flying (not driving) skills.
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Re: Final approach conundrum (stable versus safe)

Post by MackAttack »

If you are flying a standard traffic pattern at a standard altitude and a standard distance on downwind - you’re going to make the runway if the engine quits. if you are in that scenario, you aren’t going to continue to fly a standard base and final without a power plant. You’re going to put the darn thing down safely.

What I hear you saying is that you have fear that if you are flying according to the POH and somewhere on base or final, you lose the engine and you might not make the runway. Personally, I think you should practice engine out procedures until you fully understand how your airplane performs from the downwind, base and final legs with a windmilling prop and what you need to do to make the runway. What I think you’ll find is that the POH numbers for most aircraft build in the ability to make the runway with a non-op engine (better glide than with a windmilling prop) even if you lose power. A scenario where you lose the ability to make rated power in the engine but it continues to run usually isn’t as serious in the landing phase because you’re already operating at reduced power.

I did many, many “pulled to idle” short approaches while doing my tail wheel endorsement and learned to enjoy them, while learning what distance I really had to make the runway with a windmilling prop in that Carbon Cub (answer: not a whole lot). You also can’t fixate on “making the runway” in a true engine out scenario. Most of the area around the runway, taxiways and grass included, will work for you when the caca hits your rotating blades and you experience silence … you need to fixate on what it will take to make a safe landing. If on the runway, so much the better.

In short, I would practice this with a good instructor until you are confident in your knowledge of the POH and how your aircraft performs, and on the bad day when you actually have to make an engine-out landing from the pattern (or anywhere else, for that matter), it won’t be a big deal.

PS - I like the glider rating idea and have been considering that myself. But you can get proficient in this procedure in your current airplane too.
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Re: Final approach conundrum (stable versus safe)

Post by Rich »

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.
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Re: Final approach conundrum (stable versus safe)

Post by Lou »

There is a good AVWeb video on pattern flying - humorous and also sound advice. Steep approaches and tighter patterns are considered safer by some, and I agree with that approach.

For IFR I usually approach 90 knots up to the MDA and transition to landing full landing configuration after that. At 500 fpm descent that’s usually 20-30 seconds, which is lots of time.
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