- Joined
- Dec 8, 2023
- Messages
- 349
- Location
- Houston & SE Wisconsin
- Display Name
Display name:
StraightnLevel
Forward Slips with Flaps on a Practical Test
- Thread starter Revtach
- Start date
- Joined
- Apr 18, 2013
- Messages
- 4,263
- Location
- Live from the Grill-o-mat
- Display Name
Display name:
Mantis Toboggan, MD
Alternatively, it might be taken to indicate that they want the instructors to prepare their students such that >80% pass rather than changing the performance standards, and that a pass rate of <80% for a given *instructor* (not examiner) should result in a closer look at the *instructor*, as is pretty well documented in the report @Clip4 linked.
Nauga,
whose axe is dull
- Joined
- Dec 8, 2023
- Messages
- 349
- Location
- Houston & SE Wisconsin
- Display Name
Display name:
StraightnLevel
Thanks for the clarification - I misunderstood the intent.
chemgeek
En-Route
- Joined
- Dec 5, 2009
- Messages
- 3,103
- Display Name
Display name:
chemgeek
To be honest, you may not need to slip a C172 with 40 degrees of flaps to lose altitude. My primary instructor (very old school stick and rudder) showed me that a C172 has a hard time exceeding 85 knots with full 40 degrees of flaps when pointed down. Those are big barn doors. When checking out for a rental C172 at Yingling Aero in Wichita I showed the checkout pilot this while demonstrating an emergency spot landing and he was curious where I learned it and was ultimately quite OK with it. (We hit the runway landing mark right on cue.) I probably wouldn't do that with a DPE on PPL ride, though.
I did my checkride in a 172 with the O-360 engine and max 40* of flaps. Just before the last landing with the DPE, he pulled power when I was on downwind, said "you just lost your engine". I did a power off 180 slipping all the way through the downwind-base-final turn. Later I learned that the power off 180 is a commercial maneuver, but whatever - my CFI taught me how to do them and every private pilot should be able to do a power off 180.
Anyway, the point is that slips with full flaps are merely warned but not prohibited in the 172. Slipping with full flaps, the flaps may obscure the elevator and cause some pitch oscillation. This is quite rare, but it can happen. If it does, reduce the slip just enough to stabilize pitch.
Anyway, the point is that slips with full flaps are merely warned but not prohibited in the 172. Slipping with full flaps, the flaps may obscure the elevator and cause some pitch oscillation. This is quite rare, but it can happen. If it does, reduce the slip just enough to stabilize pitch.
pburger
Pre-takeoff checklist
It seems crazy to me that you would admit in a public forum that you are teaching students to ignore the POH. PLEASE STOP DOING THAT!
When the POH says, "Should be Avoided", then it's pretty clear what that means. Cessna had some reason to put that in there, and I suspect there is some data to back it up. What is your reason for declaring something to be "perfectly fine" when the manufacturer states that it "Should be avoided"? Where's your data? Is it because you "do it all the time?"
I'm a rules guy, and aviation is a rules game. Break the rules, and bad things might happen. Yes, "MIGHT", not "WILL". Therein lies the problem. You can break certain rules and get away with it some or even most of the time, which leads to confirmation bias. "I do this all the time, it's no big deal...". But there may be a time that you don't get away with it, and then you MIGHT be dead. By teaching someone to ignore the POH, you are teaching a lack of respect for rules. This is not an attitude that you want to instill in a new pilot.
A few times over the years I have flown with pilots that have blatantly broken one or more rules with me in the passenger seat (aerobatics in a Mooney, descending through a layer while VFR in mountainous terrain, etc.). Yes, they got away with it, but I don't fly with those people anymore, or if I do I will ask them very nicely not to do those things while I'm aboard.
As previously indicated, depends on the 172's vintage.
Ed Haywood
En-Route
One comment about teaching slips. Things that seem easy in practice may be too much in an emergency. Things happen FAST and you will want to limit the variables you deal with.
I'm pretty sure I have slipped as much as anyone here. My aircraft does not have flaps, so I slip on almost every landing. I routinely slip all the way to the runway and touch down as I am releasing the slip.
Yet when faced with an actual loss of power, I was uncomfortable slipping aggressively on short final.
If the last time you slipped with full flaps was during your PPL training, you are not going to be comfortable and proficient enough to do it with your life on the line.
IMO if you have 40 degree flaps, use them. That plus S turns should be sufficient to get you on the ground.
I'm pretty sure I have slipped as much as anyone here. My aircraft does not have flaps, so I slip on almost every landing. I routinely slip all the way to the runway and touch down as I am releasing the slip.
Yet when faced with an actual loss of power, I was uncomfortable slipping aggressively on short final.
If the last time you slipped with full flaps was during your PPL training, you are not going to be comfortable and proficient enough to do it with your life on the line.
IMO if you have 40 degree flaps, use them. That plus S turns should be sufficient to get you on the ground.
Last edited:
Slipping in a 172, even with the placard saying "slips with full flaps should be avoided", is not ignoring the POH.
Cessna could have said, "slips with full flaps prohibited". But they did not say that. That is the data that says it is acceptable.
It's simple: "avoid" <> "prohibited"
It means before slipping with full flaps, do a little homework to understand why Cessna wrote that, what symptoms could happen, how likely they are, and how to mitigate them if they do happen.
After doing that, the PIC is free to decide for himself whether or not to do it.
Agreed. Yet don't just read the rules, but understand what they mean.
Lindberg
Final Approach
The language in the POH, in this case, is not a limitation. Should students be taught to never exceed the max demonstrated crosswind component? Or should they be taught the reasons for what's in the POH, how to evaluate risk, and how to make good decisions?
There's a reason Cessna changed from "prohibited" to "not recommended."
Not that any of this would be great to debate on a checkride.
Much better: "Since I'm expecting to use a slip on this landing, I'm only going to use half flaps because the POH recommends against slipping with full flaps and I'll be able to sufficiently control my glidepath with the slip."
MauleSkinner
Touchdown! Greaser!
It’s also simple: “avoid” <> “perfectly fine.”
You must have a degree in Lexical Polemics.
It's not necessary to argue the difference between the terms avoid and prohibit, only to understand the meaning of avoid. I interpret "must be avoided" as meaning, don't do it.
Your argument that it's okay to disregard warnings, cautions, etc. if we do "a little homework" is dubious, at best. It certainly involves much more than "a little homework" to learn the full story behind Cessna's guidance regarding slips with full flaps, and to comprehend the implications in each and every situation in which that guidance is applicable. We are not expected to be certification test pilots during our PPL checkride. Cessna has already done all of the work for us. They have accumulated extensive expertise, gained over many decades that included design/engineering, flight testing, certification, and ongoing development programs, as well as extensive knowledge gained from worldwide fleet operations (including accident and incident investigations). For us, they have condensed all of that knowledge and expertise into a little book and a smattering of placards that we can easily read and understand so that we can operate their airplanes safely and efficiently without having to be aeronautical engineers. As for you, go do your "little homework" and come back to us in 180 days with a full report. I suspect that the enterprise may humble you.
We don't need a semanticist to interpret the AFM/POH. The language is simple and direct. Avoid means avoid. We disregard the manufacturer's guidance, in favor of random CFIs and guys on the Internet, at our peril.
It's not that, but a matter of the regulatory definition. Cessna knows the term "prohibit" has a specific regulatory meaning, and does not use it.
It's not disregarding, but knowing what the words mean. If it should never be done, if it were an aircraft limitation, if it required the skills of a certification test pilot, then Cessna would have prohibited it - but they did not.
Agreed. Every pilot should know the difference between an advisory and a prohibition.
pburger
Pre-takeoff checklist
I stand by my post.
The OP is teaching the student that it is "perfectly fine" to do something that the manufacturer says "should be avoided". Did the OP explain why it is perfectly fine? Is he qualified to make that determination? He didn't make that clear in his post. Based on what? Maybe there is more to the story.
To borrow your construction: "perfectly fine" <> "Should be Avoided"
To me this isn't about what is legal or what is specifically prohibited, but rather it's about the ATTITUDE that it conveys to a new, impressionable student pilot. I think it would be much better to teach something like, "The POH for this particular airplane says to avoid slips with full flaps, so when flying THIS airplane we're going to follow that". That seems like a better way to go than to say, "don't worry about what the POH says, I know better, it's perfectly fine, trust me"
As far as playing semantic games, that's expected on POA, but chit fire man, we're talking about a brand new student who is developing a mindset that will be with him for the rest of his life. I really think new pilots need to be mentored/shepherded to give aviation the proper respect it deserves. CFIs need to lead by example.
Last edited:
Witmo
Pattern Altitude
- Joined
- Feb 19, 2006
- Messages
- 2,434
- Display Name
Display name:
Tim
I stand corrected about slips not being a required maneuver if necessary. Your screen shot didn't actually include the part of the ACS where it talks about skills:
PA.IV.M.S7 As necessary, correlate crosswind with direction of forward slip and transition to side slip before touchdown.
I'm not saying a private pilot applicant should not know how to side or forward slip and airplane, I'm saying for the checkride why try and demonstrate a slip with full flaps when any sort of caution exists to avoid them?
There are many CFIs that should not be instructing. They really are doing a garbage job teaching.
Clip4
Touchdown! Greaser!
What quanitity is many in a percentage?
I think my CFI handled this the right way back when I was training. He read the POH with me and explained the regulatory definitions of "avoid" and "prohibited", and why Cessna would use one term versus the other.
Agreed. It's not "perfectly fine" (and I never said it was). But it is not prohibited, it is an allowed maneuver and you can do it on the checkride (as I did). The DPE may question you and if he does, you'll have the correct answer both legally & pragmatically.
Those are not my words. I'm not saying "don't worry about what the POH says". I'm saying to read the POH and understand what it actually means.
These are not semantic games. Proper understanding of the POH relies on knowing the basic regulatory definitions.
- Joined
- Jul 23, 2021
- Messages
- 3,888
- Display Name
Display name:
Albany Tom
I did my PPL in a PA-28, and have never heard of anyone having any problem with slips at full flaps, except that it really doesn't gain much. Maybe that's because a PA-28 at idle, at 1.2-1.3Vs0, at flaps 40 is already pretty steep. But what I also learned is that if you gently pull back on the flap handle a bit beyond the ratchet, you can get maybe 5 degrees more flaps and it'll come down a little steeper. Not documented anywhere. I probably wouldn't try that particular trick on a checkride, unless I knew the DPE pretty well. On the PPL checkride I demonstrated slip at full flaps and it was a non-issue.
Okay, I'll bite: What are the "regulatory definitions" of avoid and prohibited? Please cite the source of your definitions.
EdFred
Taxi to Parking
Avoid: Not recommended, but allowable.
Prohibited: Not allowed, period.
Think of it it as an MOA or W-area or A-area vs a P-area
I bet some people in this thread think demonstrated crosswind is also a limitation.
Words and their meanings matter.
We can avoid sharks by staying out of the ocean. We can avoid bears by staying out of the woods. If we do encounter sharks or bears, there are certain measures we can take.
Similarly, we “avoid” using slips at full flap setting by staying out of flight conditions which might require it. We fly correct patterns and make stabilized approaches at proper power settings. If we see that a slip will be necessary, we employ it prior to setting full flaps.
That’s not a prohibition. If we do screw up and need a slip at full flaps (this should be rare; you can go around), there are risks and we need to understand them and know how to handle possible flight behaviors.
The ACS does require demonstrating slips, but it does not require doing so at a max flap setting. Just do slips with partial flaps.
We can avoid sharks by staying out of the ocean. We can avoid bears by staying out of the woods. If we do encounter sharks or bears, there are certain measures we can take.
Similarly, we “avoid” using slips at full flap setting by staying out of flight conditions which might require it. We fly correct patterns and make stabilized approaches at proper power settings. If we see that a slip will be necessary, we employ it prior to setting full flaps.
That’s not a prohibition. If we do screw up and need a slip at full flaps (this should be rare; you can go around), there are risks and we need to understand them and know how to handle possible flight behaviors.
The ACS does require demonstrating slips, but it does not require doing so at a max flap setting. Just do slips with partial flaps.
BINGO!
"Ms DPE, I know the POH cautions against slips with full flaps, so I'm only going to 20 degrees to demonstrate the slip."
Uhhh....haven't seen Sharknado I-XXIII, have you?
What, those are the "regulatory definitions" that MRC01 referred to? Source, please.
dmspilot
Final Approach
- Joined
- Oct 20, 2006
- Messages
- 6,169
- Display Name
Display name:
DISPLAY NAME
Prohibiting slips is a problem because it's almost impossible to land without slipping a little, even if by accident. Did the aerodynamics of the 172 actually change or did they just realize that a prohibition was impractical?
Deliberately performing a slip-to-a-landing doesn't sound like "avoiding" to me. It sounds like the complete opposite of avoiding.
Deliberately performing a slip-to-a-landing doesn't sound like "avoiding" to me. It sounds like the complete opposite of avoiding.
I haven't seen an official FAA definition, but what I know is this: In the early 1990s, the late Tony Broderick was associate administrator of regulation and certification at the FAA. He was active on the Avsig online forum, and I asked him whether things in the POH had to be in the Limitations section in order to be a legal limitation. He said yes.
We were not discussing the practical test standards (which have since been renamed as the airmen certification standards), so I would not assume that this would necessarily apply on a checkride.
We were not discussing the practical test standards (which have since been renamed as the airmen certification standards), so I would not assume that this would necessarily apply on a checkride.
MauleSkinner
Touchdown! Greaser!
Sounds suspiciously like applying real-world flying to the ACS.
The checkride is about demonstrating knowledge, skill, and judgment. Depending on which variation of the "slip with flaps" comment the POH for the airplane you are taking the checkride in has, I can think of multiple ways of handling it.
When Cessna restarted production of the 172 in the 1990s, they reduced the maximum flap setting from 40 degrees to 30 degrees. However, the POH for the 172N models that I trained in (in 1991) recommended against slipping with full flaps, but did not say that say that they were prohibited. I don't know about models earlier than that.
dmspilot
Final Approach
- Joined
- Oct 20, 2006
- Messages
- 6,169
- Display Name
Display name:
DISPLAY NAME
It was changed from prohibited to avoided for the "I" (pronounced "eye") model in 1968.
The reason that MRC01 has not responded is because there are no "regulatory definitions" of the words avoid and prohibited. This is not a case of "what the meaning of the word is is." These conventional words and their meanings, as used in an AFM/POH, can be found in a dictionary of American English. Some time ago, the aviation industry went through a re-write due to new standards adopted by the FAA and other agencies. Will was out; shall was in. An emphasis was placed on using simple, standard English. At no time before or since has the aviation industry employed unique "regulatory" definitions of the words avoid and prohibited. If MRC01, or anyone else, knows differently, and can cite an authoritative source, please enlighten me.
When dinosaurs roamed the Earth and I was teaching people to fly 172s, there were many hypotheses floating around regarding the slipping-with-flaps prohibition/admonition. I won't recount them because they were then, as now, hearsay. However, one explanation given for the substitution of avoid for prohibited has nothing to do with any design changes made to the airframe--it was suggested that Cessna, as the aircraft manufacturer, has no legal authority to actually prohibit us from anything, and therefore the language in the POH was changed. That, too, may be uninformed conjecture and I only mention it to suggest that, in the absence of fact, there are any number of hypotheses that can be associated with this issue, including the OP's assertion that "slipping with full flaps extended in our C172 is perfectly fine." If our goal is to operate as safely as possible, do we adhere to the guidance provided in The Book, or do we select from one of the many alternative facts available on the Internet and elsewhere?
And that brings us back to the OP: Are his/her students in jeopardy of getting pinked if they slip a 172 with full flaps during a checkride? Is the CFI irresponsible for teaching that the guidance provided in the POH may be cavalierly disregarded based on the advice of a non-authorative source? The answers to these questions do not pivot around definitions of terms, but instead, I suggest that they are matters that fall into the category of risk management and hazardous attitudes, as used in the ACS.
When dinosaurs roamed the Earth and I was teaching people to fly 172s, there were many hypotheses floating around regarding the slipping-with-flaps prohibition/admonition. I won't recount them because they were then, as now, hearsay. However, one explanation given for the substitution of avoid for prohibited has nothing to do with any design changes made to the airframe--it was suggested that Cessna, as the aircraft manufacturer, has no legal authority to actually prohibit us from anything, and therefore the language in the POH was changed. That, too, may be uninformed conjecture and I only mention it to suggest that, in the absence of fact, there are any number of hypotheses that can be associated with this issue, including the OP's assertion that "slipping with full flaps extended in our C172 is perfectly fine." If our goal is to operate as safely as possible, do we adhere to the guidance provided in The Book, or do we select from one of the many alternative facts available on the Internet and elsewhere?
And that brings us back to the OP: Are his/her students in jeopardy of getting pinked if they slip a 172 with full flaps during a checkride? Is the CFI irresponsible for teaching that the guidance provided in the POH may be cavalierly disregarded based on the advice of a non-authorative source? The answers to these questions do not pivot around definitions of terms, but instead, I suggest that they are matters that fall into the category of risk management and hazardous attitudes, as used in the ACS.
The POH certainly can prohibit certain actions or maneuvers, for example airplanes that are not certified for intentional spins are placarded "Intentional spins prohibited" - not "avoid" but "prohibit". As @dmspilot says, early versions of the 172 said slips with full flaps were prohibited.
From the POH for the "F" model:
Later, Cessna changed that wording to "avoid".
Maybe. But I did it on my checkride and passed. During the oral before the flight the DPE raised that specific topic. First he asked whether the 15 kt max demonstrated xwind was a limitation or prohibition. Of course the answer is no. Next he asked can you slip with full flaps in this airplane. My answer was that it is not prohibited but the POH says to avoid because it may cause pitch oscillation. So you can do it if you find it necessary but watch for pitch oscillation, and if that happens then either reduce flaps or reduce the slip. The DPE nodded and we went out to fly.
FWIW, in 1500 hours of flying 172s I have never encountered this pitch oscillation.
Last edited:
There are many who are more knowledgeable that I regarding these matters, but I propose to you the following:
The POH, in and of itself, cannot prohibit anything. Limitations and prohibitions are established as a condition of type certification, by the FAA or other certification authority, and those limitations and prohibitions are published in the TCDS, the AFM/POH, and placards. It is the legal authority of the FAA (in this case) that makes the prohibited condition a prohibition, by definition. That's not to say that a manufacturer cannot use the term prohibit, only that they do not have the legal authority to make it so. They also do not have the legal authority to enforce a prohibition.
Perhaps someone with more knowledge can confirm or correct the above. But then, this vector will take us well beyond gliding distance of where we started.
Lindberg
Final Approach
Cessna's reason for changing the language is known, as is the airframe change that led to the documentation change. As is the reason the language was included to begin with. These have been discussed in this thread and ad infinitum elsewhere.
And if our only goal was to operate as safely as possible, we wouldn't take off.
Last edited:
- Joined
- Dec 8, 2023
- Messages
- 349
- Location
- Houston & SE Wisconsin
- Display Name
Display name:
StraightnLevel
You can fix that and limit the glide distance by extending the flaps and performing a forward slip.
Yes, for at least four decades. Maybe the best, on this forum, can be found in a 2015 post by the late Pilawt.
That would be not operating.
dmspilot
Final Approach
- Joined
- Oct 20, 2006
- Messages
- 6,169
- Display Name
Display name:
DISPLAY NAME
What airframe change occurred between the H and I models?
- Joined
- Apr 18, 2013
- Messages
- 4,263
- Location
- Live from the Grill-o-mat
- Display Name
Display name:
Mantis Toboggan, MD
My Cessna 172P POH (ca. 1981) has the following in the limitations section:
"Flight into known icing conditions is prohibited" (emphasis added)
"Abrupt use of the controls is prohibited above 99 knots"
"With 1/4 tank or less, prolonged uncoordinated flight is prohibited when operating on either left or right tank in level flight"
"Avoid slips with flaps extended."
Plenty of stuff is explicitly prohibited...but not slips with flaps extended.
And in the normal procedures section the landing procedures include: "Steep slips should be avoided with flap settings greater than 20°..."
and the crosswind landing technique presented includes "If flap settings greater than 20° are used in sideslips with full rudder deflection, some elevator oscillation may be felt at normal approach speeds. However, this does not affect control of the airplane." Why are they presenting techniques for slipping with flaps when they are not to be done?
Certainly there's the possibility of bad editing and revisions. I think it's more likely that there was no intention to mean you cannot slip with flaps
Nauga,
who tries to know his limitations
Last edited:
Certification limitation; see TCDS
Certification limitation, related to definition of Va; see TCDS
Not found in TCDS
Previously discussed
Slips with flaps extended are not prohibited under TC issuance.
Ask Cessna. And hey, while you have them on the line, see if you can impress upon them the fact that the contradictory language contained in their POH has created an unholy amount of dissonance for generations of pilots (quite unnecessarily, we might add) and should be resolved. If it is, in fact, "perfectly fine" to slip a 172 with full flaps, as the OP contends, they should remove from the POH and placard requirements all language to the contrary. You could also ask who issued the prohibition against uncoordinated flight with 1/4 tank or less, since it is not in the TCDS. Go at them with your best Harvey Spector impersonation.
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.
That was, originally, the intention.
It's one thing to know them. It's quite another thing to know when to push them, and when not to.
Last edited: