Forward Slips with Flaps on a Practical Test

Roger Wilco said:
Here's why my reply above is moot: Even if ongoing flight testing and operational experience determined that the whole sordid affair was a silly false alarm from the very beginning and there really is nothing to see here folks, the fact remains that Cessna once considered the act of slipping a 172 with full flaps dangerous enough to include a statement prohibiting it. And that fact could become legally admissable and potentially damaging evidence in a civil proceeding. A sharp lawyer could turn it into a hazardous "design flaw," with the right expert witness and a jury of people who think that light aircraft are noisy, polluting, dangerous rich people's toys that should be banned. Cessna's legal department probably goaded them to maintain cautionary language in the AFM/POH regarding the issue, as part of a defensive strategem.
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I find it interesting that, if the above is the case, the crack legal team "goaded them to maintain cautionary language in the AFM/POH" but let stand the narrative explicitly covering how to violate the alleged prohibition and the relatively benign flight characteristics ("some elevator oscillation may be felt at normal approach speeds. However, this does not affect control of the airplane") if one chooses to violate them.

Roger Wilco said:
It's one thing to know them. It's quite another thing to know when to push them, and when not to.
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I contend that the first sentence is a necessary but not sufficient condition for the second. I strive for both, but couldn't come up with a short tagline expressing it ;)

Nauga,
and a "push here" placard
 
nauga said:
I strive for both, but couldn't come up with a short tagline expressing it ;)
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Neither could Inspector Callahan. You could work it in as an expository element in your upcoming sequel.
 
:yeahthat:

And in that post, Cessna's Bill Thompson is quoted calling it a "caution note," not a prohibition.
 
Lindberg said:
Did you read that post before you linked to it? It actually answers most of the questions to seem to still be struggling with.
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Why, yes I did read that post, which is I why I characterized it as being "maybe the best." I had previously read Thompson's account on a different forum.

Just to be clear, I am not struggling with any questions here, Charlie. But thanks just the same.
 
Thank you all.

I'm going to go with having students demonstrate the forward slip as part of a flaps up landing on the practical, just to be safe.
 
Revtach said:
Thank you all.

I'm going to go with having students demonstrate the forward slip as part of a flaps up landing on the practical, just to be safe.
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I think that's the best way to prepare your students for the ride.

The thread drove off into the weeds, what with the bickering over the definitions of words etc. My fault, so please let me restate my position in a way that might be more accurate, succinct, and meaningful:

Here's the way I see it, from a philosophical standpoint: We are not teaching students to fly a 172, we are using a 172 to teach students to fly. There is an important distinction in that statement. The attitudes and habits that students learn under our tutelage will stay with them, and I propose that we do students no favors by teaching them to disregard the guidance provided in the AFM/POH. As a matter of best practices, I suggest that our goal should be to teach them to respect, and operate in compliance with, that guidance, regardless of which aircraft they may fly.

Best of luck to your applicants. I'm sure that you have prepared them for success.
 
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Revtach said:
Thank you all.

I'm going to go with having students demonstrate the forward slip as part of a flaps up landing on the practical, just to be safe.
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That sounds like a reasonable approach for the test.

However, pragmatically speaking, when landing an airplane equipped with flaps, one would normally use flaps first, and slip only if flaps were not sufficient. That means when performing a forward slip to land, it would usually be with full flaps. And conversely, it would be less common to slip to landing without having flaps deployed.
 
MRC01 said:
That means when performing a forward slip to land, it would usually be with full flaps. And conversely, it would be less common to slip to landing without having flaps deployed.
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More likely to be high when flaps are not being used. Therefore, it would be more common to slip to landing without having flaps deployed.
 
dmspilot said:
More likely to be high when flaps are not being used. Therefore, it would be more common to slip to landing without having flaps deployed.
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If you're too high, then the first steps should be to throttle back (if you're not already at idle) and deploy flaps (if they're not already deployed).
After doing that, if you're still too high then you can slip to descend faster without increasing speed.

In airplanes equipped with flaps the normal landing sequence does not involve slipping. Forward slip to landing is used when you need a steeper than normal approach.

Put differently: what's the point of slipping if you have flaps and are not already using them? Maybe the flaps are defective, etc. but those are not normal situations.
 
MRC01 said:
If you're too high, then the first steps should be to throttle back (if you're not already at idle) and deploy flaps (if they're not already deployed).
After doing that, if you're still too high then you can slip to descend faster without increasing speed.

In airplanes equipped with flaps the normal landing sequence does not involve slipping. Forward slip to landing is used when you need a steeper than normal approach.

Put differently: what's the point of slipping if you have flaps and are not already using them? Maybe the flaps are defective, etc. but those are not normal situations.
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It is also not a normal situation to slip an airplane with full flaps when the manufacturer recommends against it.

There is a certain suspension of reality when giving/taking a checkride. A forward slip is required for landing at some point…that right there is a suspension of reality for a lot of pilots. But rather than pretending you screwed up a normal approach and doing something counter to manufacturer’s recommendations as a solution, maybe pretending the flaps don’t work would be a better option.
 
Note that "full flaps" in the C-172 models that are so placarded means 40* of flap. If you have only 30* of flap then it's not "full" and the advisory to avoid slips no longer applies.

Consequently, one practical approach to this issue is to limit the 40* flaps to 30*. Then, you get +100 # to the gross weight (for example the Deltahawk STC), and you don't have to worry about slipping with "full flaps" because the airplane is no longer capable of the "full flaps" to which the advisory originally referred.
 
MRC01 said:
That sounds like a reasonable approach for the test.

However, pragmatically speaking, when landing an airplane equipped with flaps, one would normally use flaps first, and slip only if flaps were not sufficient. That means when performing a forward slip to land, it would usually be with full flaps. And conversely, it would be less common to slip to landing without having flaps deployed.
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Why is using flaps necessarily better than using a slip, even in an aircraft equipped with them?
 
Roger Wilco said:
The attitudes and habits that students learn under our tutelage will stay with them, and I propose that we do students no favors by teaching them to disregard the guidance provided in the AFM/POH.
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You're very hung up on this strawman. No one is suggesting students be taught to disregard the POH. Rather, students should be taught to actually understand the POH and take that understanding into account in their risk-assessment and ADM processes.
 
Half Fast said:
Flaps increase lift, reduce the stall speed, and allow a slower landing. A slip doesn’t.
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They also increase drag. And they don't compensate for crosswinds. It's also generally not a good idea to vary them on short final.
 
Lindberg said:
You're very hung up on this strawman. No one is suggesting students be taught to disregard the POH. Rather, students should be taught to actually understand the POH and take that understanding into account in their risk-assessment and ADM processes.
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At this point--almost 100 posts deep--those who get it, get it. Those who don't, don't.
 
Lindberg said:
They also increase drag.
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That's a feature, not a bug. Increasing drag enables you to descend faster without increasing speed accordingly. Of course, a slip does the same (increases drag). But as @Half Fast says, a slip doesn't also increase lift and reduce the stall speed, as flaps do. That's why the normal procedure is to use flaps first, then slip if that's not steep enough.

Note that I intentionally avoided using the word "better". What is "better" depends on the situation and the pilot's judgement.

Lindberg said:
And they don't compensate for crosswinds.
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Of course a crosswind landing is also a kind of forward slip, having opposite rudder & aileron input. That's a whole 'nuther subject.

Roger Wilco said:
At this point--almost 100 posts deep--those who get it, get it. Those who don't, don't.
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Well, "get it" could mean understand the point, or it could mean agree with the point. These are independent.
 
MRC01 said:
That's why the normal procedure is to use flaps first, then slip if that's not steep enough.
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And if you’re talking about “not steep enough” in a Cessna single with 40 degrees of flaps, you’ve screwed up so badly that good ADM dictates a go around anyway.
 
MauleSkinner said:
And if you’re talking about “not steep enough” in a Cessna single with 40 degrees of flaps, you’ve screwed up so badly that good ADM dictates a go around anyway.
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Normally and most of the time, true. Though there are unusual situations where it might be useful, like having to clear tall trees or other obstacles on final approach.
 
MRC01 said:
Normally and most of the time, true. Though there are unusual situations where it might be useful, like having to clear tall trees or other obstacles on final approach.
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In which case you’d probably get a steeper descent with less flaps and a slip.
 
Not to add to any argument, in part because I can't see arguing about any of this, but couple of other things.

Quicker to undo a slip than flaps for a go-around. Not sure how that may be helpful, but it could reduce risk of stall in taking out flaps before you have the airspeed.
The last notch of flaps in some aircraft isn't giving you any significant additional lift or reducing stall speed, it's just more drag.
Slipping looks cool and is more fun than flaps.
Pretty sure there's no such thing as an asymmetrical slip deployment.

But I use full flaps for landing in a PA-28 almost always. (Partly because my approach estimates are almost always leaving me a little too high.)
 
Wow--where's the OFF switch on this thing?

I know I shouldn't do this, but...

We teach students how, and when, to use slips because they are (at least in light aircraft) a useful maneuver that also improves stick-&-rudder skills. And because many light aircraft (especially gliders) don't have flaps at all. Flying aircraft with flaps, we teach students when, how, and why to use the increased drag and lift that they provide. We also teach them how to safely execute go-arounds and missed approaches with flaps fully extended. Approaches are normally planned so as to utilize flaps to achieve the desired descent path and to provide an approach speed that's appropriate for the situation and conditions. Further training teaches students how to use a slip to accomplish much the same objectives.

However imprecisely stated, maybe we can agree on the preceding. But now let me try to screw it up by going back to the OP, in which the 172 represents a bit of a special case. Depending on which model we fly, slips with 40 flaps are prohibited or should be avoided. Given that official guidance, when WOULD it be appropriate to execute a slip with flaps 40? Always? Never? Depends? Obviously it's been done countless times without newsworthy results, but there must be some reason why that language is in The Book.

With respect to both the POH and the real world, I suggest that the following represent circumstances in which it is reasonable to extend flaps 40 and throw her into as much of a slip as is necessary to keep us out of the news: Certain do-or-die scenarios, such as 1). finding ourselves too high/fast on final to a one-way runway in the mountains, where a survivable go-around is doubtful; 2). A similar predicament after an engine failure, in which we're too high/fast to put-her-down on our chosen landing surface, but without better options. Those cases are not exclusive, and we may envision other dire circumstances in which we have to get the plane on the ground and stopped, here and now.

Apropos the OP: If I were a DPE evaluating PPL applicants in 172s, I would be interested in seeing them demonstrate their skill and judgement by planning and flying approaches ICW the POH/AFM so that it is not necessary to slip the airplane with 40 flaps. That, I think, is a reasonable standard of airmanship to expect of a pilot during a checkride; one who seeks a ticket to carry passengers off into the wild blue. That said, should an applicant misjudge the dead stick landing exercise (which could happen to any of us on any given day) and recover by slipping the plane with flaps 40 in order to save the day, that might be considered a successful outcome (real world). But in no case would I consider it acceptable to treat slips with flaps 40 as a "perfectly fine" SOP, contrary to the manufacturer's published guidance. And lastly, I maintain that it is important to teach students to respect and comply with the guidance provided by the manufacturer in the AFM/POH/placards, and only deviate from that guidance if compelling circumstances demand such action.

Much of this has been said by others and I'm not sure if there is anything left worth debating, so I'm going to clear the frequency. Roger Wilco, over-and-out.
 
Roger Wilco said:
Wow--where's the OFF switch on this thing?

I know I shouldn't do this, but...

We teach students how, and when, to use slips because they are (at least in light aircraft) a useful maneuver that also improves stick-&-rudder skills. And because many light aircraft (especially gliders) don't have flaps at all. Flying aircraft with flaps, we teach students when, how, and why to use the increased drag and lift that they provide. We also teach them how to safely execute go-arounds and missed approaches with flaps fully extended. Approaches are normally planned so as to utilize flaps to achieve the desired descent path and to provide an approach speed that's appropriate for the situation and conditions. Further training teaches students how to use a slip to accomplish much the same objectives.

However imprecisely stated, maybe we can agree on the preceding. But now let me try to screw it up by going back to the OP, in which the 172 represents a bit of a special case. Depending on which model we fly, slips with 40 flaps are prohibited or should be avoided. Given that official guidance, when WOULD it be appropriate to execute a slip with flaps 40? Always? Never? Depends? Obviously it's been done countless times without newsworthy results, but there must be some reason why that language is in The Book.

With respect to both the POH and the real world, I suggest that the following represent circumstances in which it is reasonable to extend flaps 40 and throw her into as much of a slip as is necessary to keep us out of the news: Certain do-or-die scenarios, such as 1). finding ourselves too high/fast on final to a one-way runway in the mountains, where a survivable go-around is doubtful; 2). A similar predicament after an engine failure, in which we're too high/fast to put-her-down on our chosen landing surface, but without better options. Those cases are not exclusive, and we may envision other dire circumstances in which we have to get the plane on the ground and stopped, here and now.

Apropos the OP: If I were a DPE evaluating PPL applicants in 172s, I would be interested in seeing them demonstrate their skill and judgement by planning and flying approaches ICW the POH/AFM so that it is not necessary to slip the airplane with 40 flaps. That, I think, is a reasonable standard of airmanship to expect of a pilot during a checkride; one who seeks a ticket to carry passengers off into the wild blue. That said, should an applicant misjudge the dead stick landing exercise (which could happen to any of us on any given day) and recover by slipping the plane with flaps 40 in order to save the day, that might be considered a successful outcome (real world). But in no case would I consider it acceptable to treat slips with flaps 40 as a "perfectly fine" SOP, contrary to the manufacturer's published guidance. And lastly, I maintain that it is important to teach students to respect and comply with the guidance provided by the manufacturer in the AFM/POH/placards, and only deviate from that guidance if compelling circumstances demand such action.

Much of this has been said by others and I'm not sure if there is anything left worth debating, so I'm going to clear the frequency. Roger Wilco, over-and-out.
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Lot of words.

Do you have any real confined airfield experience? A short strip with tall trees? Where the flaps can help you steepen the approach, making the aiming point steady, but where, once inside the 75'+ tall trees (there are no 50' ones in my experience), you need to slip to get the thing down in a reasonable space?

Have you slipped a 172 or 182 with flaps out? Are you under the impression that the aircraft will immediately dive for the ground in an uncontrollable manner?

As far a a check ride, no DPE is going to take you to the kind of field where both full flaps and a slip are needed to hit the spot anyhow. It's probably the one time where if you can't manage the energy needed with power and flaps without using a slip other than to correct for a crosswind in the flare, you probably should get more training.

And as others have already pointed out, in a regulated area, words have specific meanings that may or may not overlap with their everyday usage. So a limitation is different than a recommendation against.
 
MRC01 said:
That's a feature, not a bug. Increasing drag enables you to descend faster without increasing speed accordingly. Of course, a slip does the same (increases drag). But as @Half Fast says, a slip doesn't also increase lift and reduce the stall speed, as flaps do. That's why the normal procedure is to use flaps first, then slip if that's not steep enough.

Note that I intentionally avoided using the word "better". What is "better" depends on the situation and the pilot's judgement.


Of course a crosswind landing is also a kind of forward slip, having opposite rudder & aileron input. That's a whole 'nuther subject.


Well, "get it" could mean understand the point, or it could mean agree with the point. These are independent.
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The difference in stall speed between no flaps and full flaps in a PA-18 is a couple of knots. But the difference in controllability between one notch of flaps plus slipping vs. straight to full flaps is significant.
 
When the aircraft is not one of the model years that has the pitch down tendency, slipping with full flaps can become essential if you find yourself too high while landing with a dead engine in a single.
 
Steamflyer said:
As far a a check ride, no DPE is going to take you to the kind of field where both full flaps and a slip are needed to hit the spot anyhow.
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Not true.

The DPE put me in that position on my PPL checkride intentionally to see if I would use a forward slip. He set up an emergency engine-out scenario to force it; a very small spot where I had too much altitude to land, but not enough to use a 360. This was in a PA28, not a C172, but the expectation was clear; I slipped it with full flaps, and passed the checkride.
 
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