Power Off 180, CFI Says X, I Say Y

[loganjvx]

Good Afternoon POA members,

I have a question regarding a disagreement my instructor and I had during a ground brief today. I am a CFI-A applicant and was teaching commercial maneuvers, including the Power-Off 180 accuracy landing, as part of my training. While I was instructing him on the maneuver, he presented a scenario-based question regarding aerodynamic theory that led to a disagreement between us.

Scenario:

• You are flying a Power-Off 180 in the traffic pattern
• You are turning from base to final
• The wind is from right to left at approximately 8 knots
• During the turn, you realize you are high and need to lose altitude
• You must decide whether a forward slip is appropriate
• If so, you must determine which direction to slip

Before discussing the appropriate action given these circumstances, it is important to review the purpose of the Power-Off 180 as outlined in the Airplane Flying Handbook and the ACS. The AFH states, “The objective is to further develop judgment in estimating distances and glide ratios, in that the airplane is flown without power from a higher altitude and through a 90° turn to reach the base leg position at a proper altitude for executing the 90° approach.” The CFI ACS describes the Power-Off 180 Accuracy Approach and Landing as a maneuver in which power is reduced to idle abeam a selected touchdown point and the airplane glides to land at or within 200 feet beyond that point without adding power. The purpose is to demonstrate precise energy management, wind correction, planning, and stabilized approach control. The AFH defines a forward slip as a cross-controlled maneuver used to increase drag and rate of descent while minimizing airspeed gain during an approach to landing.

My position was that you should not perform a forward slip in the turn, regardless of wind direction. In this scenario, you are flying at best glide at a low altitude of approximately 350 to 500 feet AGL. You are also in a turn, where stall speed is already increased due to load factor and the reduced vertical component of lift. Introducing a slip and cross-controlled inputs would further increase stall speed and increase the risk of exceeding the critical angle of attack. At that altitude, a stall spin event would likely be unrecoverable.

My argument was that if slipping in the turn is your only option to make the runway, the approach was mismanaged earlier. You could have adjusted your ground track, configured earlier with flaps, or performed a slip on base or final in coordinated, wings-level flight. I also question the instructional value of teaching a low-altitude, cross-controlled maneuver in a turn to a student pilot and presenting it as acceptable risk management.

My instructor’s position is that a forward slip is appropriate in this situation if executed properly. He argues that using right rudder in a left turn to induce a skid can be accomplished safely with proper control and awareness.

I am interested in hearing your thoughts and perspectives on this scenario.

 

[Rick A]

My instructor’s position is that a forward slip is appropriate in this situation if executed properly. He argues that using right rudder in a left turn to induce a skid can be accomplished safely with proper control and awareness.

I am interested in hearing your thoughts and perspectives on this scenario.

I'm with your instructor.

Nothing wrong with slips as long as the nose remains lowered and the increase in airspeed is NOT countered by an increase in angle of attack during the uncoordinated maneuver.

Position the aircraft to allow an appropriate short segment of deceleration enabling any increase in airspeed that occurred during the slip to bleed off only AFTER coordinated flight is resumed. Then a normal power-off landing attitude and airspeed can be established on final.

This may take a little practice, but slips and skids are nothing to be feared when done properly. Like always, pulling back on the yoke is the killer when done at the wrong time and airspeed, regardless of whether coordinated, or not.

 

[flyingcheesehead]

I have a question regarding a disagreement my instructor and I had during a ground brief today. I am a CFI-A applicant and was teaching commercial maneuvers, including the Power-Off 180 accuracy landing, as part of my training. While I was instructing him on the maneuver, he presented a scenario-based question regarding aerodynamic theory that led to a disagreement between us.

... And I think you're both right, and you're both wrong.

My position was that you should not perform a forward slip in the turn, regardless of wind direction. In this scenario, you are flying at best glide at a low altitude of approximately 350 to 500 feet AGL. You are also in a turn, where stall speed is already increased due to load factor and the reduced vertical component of lift. Introducing a slip and cross-controlled inputs would further increase stall speed and increase the risk of exceeding the critical angle of attack. At that altitude, a stall spin event would likely be unrecoverable.

It's not necessarily bad to perform a slip in a turn, but you definitely need to be extra vigilant for the reasons you stated.

My argument was that if slipping in the turn is your only option to make the runway, the approach was mismanaged earlier.

True.

You could have adjusted your ground track, configured earlier with flaps, or performed a slip on base or final in coordinated, wings-level flight. I also question the instructional value of teaching a low-altitude, cross-controlled maneuver in a turn to a student pilot and presenting it as acceptable risk management.

This. And for that reason, I favor your answer over your instructor's.

You don't need to "win" this argument. Just go forth and do well on the checkride and teach your students appropriately, it sounds like you have the right ideas. As for your CFI, I doubt he's actually telling students to do this, it sounds like a theoretical scenario more so than a real one. (I hope.)

My instructor’s position is that a forward slip is appropriate in this situation if executed properly. He argues that using right rudder in a left turn to induce a skid can be accomplished safely with proper control and awareness.

Right rudder in a left turn isn't a skid... But skidding turns are the dangerous ones that lead to unrecoverable stall/spins in the pattern and should never be done at low altitude or anywhere near the stall.

For that reason, if I absolutely must accomplish this maneuver on this attempt (ie, my engine has failed), I would use right rudder in the left turn (slipping, not skidding) regardless of wind direction. It wouldn't take much, though.

 

[farangutan]

Turning slips base to final should absolutely be in your toolbox. Go to your practice area and stall the plane in a turning slip to feel more comfortable. You already know what you risk stalling in a skidding turn. Better yet, fly a plane that doesn't have flaps and you'll use turning slips base to final much more often.

 

[Lindberg]

He's right.

My argument was that if slipping in the turn is your only option to make the runway, the approach was mismanaged earlier. You could have adjusted your ground track, configured earlier with flaps, or performed a slip on base or final in coordinated, wings-level flight.

So your solution is a time machine? You can only get to the runway from where you are, not where you were.

I also question the instructional value of teaching a low-altitude, cross-controlled maneuver in a turn to a student pilot and presenting it as acceptable risk management.

How would you teach students to fly a no-spoiler glider pattern?

My instructor’s position is that a forward slip is appropriate in this situation if executed properly. He argues that using right rudder in a left turn to induce a skid can be accomplished safely with proper control and awareness.

Right rudder in a left turn will induce a slip, not a skid. And he's right. You should practice slips at altitude, including stalling, until you're comfortable with them.

If you're flying the maneuver at best glide, another option is to slow down, which will increase your sink rate. You can also make S turns, etc. But slipping is a good flexible option.

 

[Dan Thomas]

My instructor’s position is that a forward slip is appropriate in this situation if executed properly. He argues that using right rudder in a left turn to induce a skid can be accomplished safely with proper control and awareness.

Forward slips are safe. We taught them all the time, and slipping turns were also handy.

But deliberate skidding? Never. That IS asking for a stall/spin. We used to demonstrate that at altitude in the Champ or Citabrias. The student experiences that once and he never skids in the pattern again.

 

[RussR]

You should be able to safely slip all the way from downwind to landing, through both turns and the straight segments. Go practice it, it's fun and safe and is a good skill to have. For some airplanes (mostly those without flaps) it's actually a normal landing practice.

The wonderful thing about a slip, of course, is that once you've corrected your glidepath problem, you just un-slip and you're immediately back to normal flight. It's an immediate on/off switch for adding drag. Much like speedbrakes in planes that have them (but of course not many of those are being used for commercial training, some but not many).

 

[Capt. Geoffrey Thorpe]

What are these "flaps" of which you speak?

In a Cessna 120 (what I learned to fly in) you run out of rudder before you run out of aileron in a hard slip. In my current ride (E-AB) you run out of stick before you run out of rudder. But in either case, if you find yourself high, that's the way to get down. Or, if you are faced with a short landing area, a hard slip after you clear the wires / trees helps a lot.

Engine out, I would rather be a little high than low. High is easy to fix. Low is not.

 

[decalogue]

A slip is fine, I’d bank into the wind, if a applicant can not execute a slip in the above scenario they are not ready for solo.

Have you done much upset training, falling leaf stalls, spins?

 

[brcase]

My thoughts—

To simplify the discussion, let’s assume you are flying an airplane without flaps. I do this in a Cessna 120 fairly often.

You should be flying the approach at a normal approach speed, which is usually close to Vy, typically around 1.4 × stall speed (Vs). You should not be anywhere near stall speed at this point.

Regarding “The wind is from right to left at approximately 8 knots”: I’m not completely sure what is meant, but I will assume an 8‑knot crosswind across the runway while flying a standard left-hand pattern.

Ideally, you would add about 4 knots on your base leg to achieve the best glide speed for the conditions, assuming you haven’t yet realized that you’re high. If you do realize you’re high, you can slow to about 1.2 × Vs, which will give you a steeper approach angle due to the reduced speed.

So, let’s say you recognize too late that you’re high and need to slip. Generally, right rudder is the easiest option because you are already turning (or about to turn) left for the base‑to‑final turn, so the aircraft is already banked left. This also gives you the best view of the runway. You should already be at least at 1.2 × Vs, so as long as you maintain airspeed, a stall is impossible without Maneuvering to pull G's (at least 1.44G's)

Many trainers have their static port only on the left side of the aircraft. As you add right rudder, the airspeed indicator tends to show a decrease; if you simply maintain the indicated airspeed, your actual airspeed will be higher. Also, remember your aerodynamics: drag increases with the square of airspeed. A small increase in speed creates a large increase in drag. This increase in airspeed will push even further away from the stall speed. So pushing the nose down a bit and gaining a little speed in the slip isn’t a bad thing to help lose altitude—just remember you’ll need to bleed that speed off before touchdown.

Now, regarding the right crosswind: You’ve pressed right rudder and banked enough to continue the turn so the aircraft’s track aligns with the runway. The nose will be pointed noticeably to the right. Once aligned, you start rolling out of the steep left bank (steep bank also helps lose more altitude). With a right crosswind, you roll out earlier to stop the turn and then hold enough crosswind correction to stay on the centerline.

As I talk through this, I can’t think of a good reason to use a left‑rudder slip in this scenario. That would require rolling from a left bank into a right bank to establish the slip. It also generally provides worse runway visibility from the pilot’s seat in many aircraft. In some planes, flying from the right seat improves visibility, but you would still have to roll from a left bank into a right bank.

While a left‑rudder slip might technically align the nose better with the runway in a right crosswind, in practical terms there’s really no significant advantage in this scenario.

Brian
CFII/ASEL

 

[dtuuri]

Except for misspeaking (you said skid for a slip) you are right. Slipping toward the left shortens your track to the runway. You are high, so you want to extend it not shorten it. So, you need to shallow the bank then come back to final from the opposite side. At that time, you can slip toward the wind (to the right) if still high. That will give you a headwind component and require a less severe slip.

 

[Salty]

Tell a tailgdragger biplane pilot they shouldn’t slip in the base turn and wait awhile for the laughter to stop.

 

[MauleSkinner]

I’m with the “add left aileron and right rudder” crowd. A forward slip in a turn is not a problem. Flaps or not really doesn’t play into it.

I’d also bet that the question wasn’t about “whether you should,” but rather about changing direction of the slip from forward slip left wing down to sideslip right wing down. You just managed to dig yourself into an unrelated hole.

And as @Lindberg noted, it’s not about going back in time and doing it perfectly, it’s about correcting a common error, which is part of the teaching process that you’re trying to learn.

 

[schmookeeg]

The point of the scenario is to save your ass, not argue aerodynamic minutia or risk management. You already lost the "risk" cointoss by losing the engine, so risk mitigations are secondary.

Doesn't matter what either of you think -- it will matter what the DPE on your initial thinks

 

[dtuuri]

OP: We've been surrounded and outnumbered, but I have a way to flip the script. Of course, you need to escape from your instructor's misguided position first, which a simple, "Gee, that's a good point," ought to accomplish as you move on to something else. Next, if the DPE poses the same scenario, you could first refer to the professional way of doing things under the "Critical Success Factor" of "The conservative response to challenge", as exemplified in this document: https://flightsafety.org/ap/ap_aug91.pdf. Then, just recite my answer.

 

[Lindberg]

Slipping toward the left shortens your track to the runway.

How so?

 

[dtuuri]

How so?

The easiest explanation is to open the left side window and see if the relative wind hits your face. That's your new track, left more toward the runway, from the previous track.

 

[RyanShort1]

My argument was that if slipping in the turn is your only option to make the runway, the approach was mismanaged earlier. You could have adjusted your ground track, configured earlier with flaps, or performed a slip on base or final in coordinated, wings-level flight. I also question the instructional value of teaching a low-altitude, cross-controlled maneuver in a turn to a student pilot and presenting it as acceptable risk management.

Ok, but there can be reasons why the initial approach was mismanaged, or wasn't an option, so you should still want your instructor's option as a tool in your toolbox.

 

[MauleSkinner]

The easiest explanation is to open the left side window and see if the relative wind hits your face. That's your new track, left more toward the runway, from the previous track.

So when you enter a forward slip your heading doesn’t change?

 

[decalogue]

OP: We've been surrounded and outnumbered, but I have a way to flip the script. Of course, you need to escape from your instructor's misguided position first, which a simple, "Gee, that's a good point," ought to accomplish as you move on to something else. Next, if the DPE poses the same scenario, you could first refer to the professional way of doing things under the "Critical Success Factor" of "The conservative response to challenge", as exemplified in this document: https://flightsafety.org/ap/ap_aug91.pdf. Then, just recite my answer.

Funny enough I had a guy like that a year or two ago, pre solo, he knew EVERYTHING right or wrong he was 100% confident he had the right answer. I tired to talk to him about this stichk and he’s use those PC/HR phrases like “that’s a good point” I fired him as a student, and later so did a few other CFIs.

He should have just written OKC letting them know he already knows everything, maybe they’d have mailed him back a full ATP and wright brothers award lol

 

[dtuuri]

So when you enter a forward slip your heading doesn’t change?

It's not a forward slip if you're in a turn. It's just a slipping turn. While I'm on my soap box, forward slips and side slips are the same except for the reference point on the ground. A forward slip to 36 could also be a side slip 03 if the runway beginnings are close to each other.

 

[Lindberg]

It's not a forward slip if you're in a turn. It's just a slipping turn.

What's the difference between a slip and a slipping turn?

And does slipping in a turn increase or decrease the turn radius as compared to a coordinated turn?

 

[decalogue]

What's the difference between a slip and a slipping turn?

And does slipping in a turn increase or decrease the turn radius as compared to a coordinated turn?

What may be fog to you may also be a cloud to a cat

 

[MauleSkinner]

It's not a forward slip if you're in a turn. It's just a slipping turn. While I'm on my soap box, forward slips and side slips are the same except for the reference point on the ground. A forward slip to 36 could also be a side slip 03 if the runway beginnings are close to each other.

Ok…so when you enter a slipping turn your heading change doesn’t change?

(p.s. I like the fact that you add another name for things that are the same.)

 

[Rick A]

Ok, but there can be reasons why the initial approach was mismanaged, or wasn't an option, so you should still want your instructor's option as a tool in your toolbox.

Absolutely. It's another stick and rudder skill set. And an important one.

Imagine navigating to a reachable runway following an engine failure, then popping out of the clouds at 300' AGL and finding yourself too high. You've got one shot at it. Stick and rudder skills could be the difference between landing on the runway, or in the trees, or at a housing development.

Stick and rudder skill sets can atrophy without use... especially in an environment where autopilots are recommended and often declared a safer and more precise way to travel from A to B.

 

[Lindberg]

Absolutely. It's another stick and rudder skill set. And an important one.

Imagine navigating to a reachable runway following an engine failure, then popping out of the clouds at 300' AGL and finding yourself too high. You've got one shot at it. Stick and rudder skills could be the difference between landing on the runway, or in the trees, or at a housing development.

Stick and rudder skill sets can atrophy without use... especially in an environment where autopilots are recommended and often declared a safer and more precise way to travel from A to B.

We don't even need to be that dramatic. Imagine you're on your check ride and the winds are slightly different than anticipated or you get a gust or your pattern wasn't perfect or you drop the flaps a little too late or . . . . Do you want to pass or not?

On my commercial ride, the examiner was certain I was going to miss the target. I didn't because I know how to slip.

The procedure is the same everyday: Do what needs to be done.

 

[dtuuri]

What's the difference between a slip and a slipping turn?

Aerodynamically, none. A "forward" slip is along the runway centerline with the longitudinal axis at an angle. A "side" slip approaches from the side with the axis parallel to the centerline.

And does slipping in a turn increase or decrease the turn radius as compared to a coordinated turn?

Decreases the rate. If you slip enough, it stops it completely on a straight path (not curved) to the runway.

 

[MauleSkinner]

Decrease. If you slip enough, it stops it completely on a straight path (not curved) to the runway.

Interesting…when I do a slipping turn, I add bank to maintain my turn.

 

[Lindberg]

Aerodynamically, none.

Agreed.

A "forward" slip is along the runway centerline with the longitudinal axis at an angle. A "side" slip approaches from the side with the axis parallel to the centerline.

Neither of these statements is necessarily true. Slips can be done without any reference to a runway.

Decrease. If you slip enough, it stops it completely on a straight path (not curved) to the runway.

Wait, so a straight line has a smaller radius than a turn? I'm now questioning everything I know about geometry.

 

[dtuuri]

I'm now questioning everything I know about geometry.

I’m questioning everything you know about slips. EDIT: See my edit above. Was thinking in terms of rate.

 

[Salty]

Interesting…when I do a slipping turn, I add bank to maintain my turn.

I don't think it would be a slip unless you do what you said.

 

[Lindberg]

I’m questioning everything you know about slips. EDIT: See my edit above. Was thinking in terms of rate.

Wait, so you're questioning my knowledge because you were wrong and I pointed it out? I didn't ask about rate, I asked about radius. I'm still trying to figure out why you say a slipping turn shortens your track to the runway as compared to a coordinated turn.

 

[Lindberg]

I don't think it would be a slip unless you do what you said.

You can use increased bank or top rudder.

 

[Hengelo]

The comment above "you're both right" resonates for me. There is a lot to be learned in the discussion, and nothing to be gained by "being right."

 

[Rick A]

We don't even need to be that dramatic. Imagine you're on your check ride and the winds are slightly different than anticipated or you get a gust or your pattern wasn't perfect or you drop the flaps a little too late or . . . . Do you want to pass or not?

On my commercial ride, the examiner was certain I was going to miss the target. I didn't because I know how to slip.

The procedure is the same everyday: Do what needs to be done.

Good points. I never think in terms of passing check rides... but only when, as you say, "Do what needs to be done".

My plane is slick, even with the gear down. At times, if trending too high, I prefer to slip it on final rather than chopping throttle or jockeying power (which I am loath to do). Slips are silent, and smooth.

A not so uncommon situation that initiates conducting a slip (rather than throttle adjustments when visual) is having the winds on final change, or not being even close to what was expected, i.e. finding calm air, or experiencing a tailwind.

IMO, using slips to lose altitude, even when other methods are available for getting back onto a desired glide path, is good stick and rudder practice, and quite natural.

 

[dtuuri]

Wait, so you're questioning my knowledge because you were wrong and I pointed it out? I didn't ask about rate, I asked about radius. I'm still trying to figure out why you say a slipping turn shortens your track to the runway as compared to a coordinated turn.

I pictured holding a heading tangent to the original turn’s path while slipping. It seems obvious the path would change inward. I guess you could picture it in a way that changes the heading to the outside. I see that as taking liberties with the scenario given. Bottom line to me is to use the least correction needed. Least bank, least slip, least skill level, least uncomfortable, etc.

 

[decalogue]

 

[MauleSkinner]

Bottom line to me is to use the least correction needed. Least bank, least slip, least skill level, least uncomfortable, etc.

Seems like that would be an increase in Bank to keep the turning path where it was planned rather than over- or undershooting the turn and having to make a lateral path correction in addition to the vertical one.

 

[Lindberg]

I pictured holding a heading tangent to the original turn’s path while slipping. It seems obvious the path would change inward. I guess you could picture it in a way that changes the heading to the outside. I see that as taking liberties with the scenario given. Bottom line to me is to use the least correction needed. Least bank, least slip, least skill level, least uncomfortable, etc.

My inadequate geometry is really failing me today. Aren't tangents outside the circle?

The problem given was you are on the base to final turn and are high, do you slip?

While still in the turn, adding top rudder will make you slip and reduce the rate of turn. Your sink rate will increase and it won't shorten your horizontal track to the runaway. If anything, it will increase it. If you're at or nearing the end of the turn, a slip on final is a no-brainer and won't affect your horizontal track at all.

 

[Albany Tom]

I think the important take away is that slipping is a skill everyone should have. Plus it's fun.

The side note is that reading people talk about slipping is much less fun.

Slips increase drag. Increased drag leads to steeper descent angle. Steeper descent angle leads to a way to fix being too high. Simple stuff.