The International Cessna^® 170 Association

The discussion of the recent 170B accident in OK provokes me to admit personal stoopidity in my young CFI days….in the hopes of reinforcing the Warning and encouraging spreading the news….Do Not Slip a 170-B or 172/SkyHawk with Full (40*) Flaps extended.

While it was not “prohibited” due to earlier certification req’s…that was a “Caution” or “Warning” issued…. and unfortunately overlooked, perhaps because stronger wording was not provided.

Some folks have commented words to the effect that “it’s not really a problem” or such… and some folks even experimented with the maneuver (hopefully at altitude…where plenty of recovery might be available…but nevertheless it is still a maneuver which violates the precautionary statement. I.E., there is no “altitude” at which a slip with full flaps is considered “safe”.)
If the airplane were to undergo recertification under present day rules I’m pretty certain it would be a “prohibited” maneuver…not merely a precautionary recommendation.

My admission: When I was in my early 20’s and working as a free-lance instructor, one of my students asked me about the precautionary statement he found in his early 172. I asked MY instructor…Steve….an older guy (40-ish) and he said there was no reason he knew of…. and since I believed Steve was all-knowing… I went out in a 172 and did a few slips with full flaps and found nothing peculiar other than a very steep decent.
Subsequently I told MY student that it was probably just Cessna being extra-carefull because of the steeper-than-ordinary descent….. and so we went out on a lesson and I showed him how it worked.

We did several…. and not at high altitude… actually at least once during a simulated engine-out approach to a farmers-field. Fortunately, nothing out-of-the ordinary steep descent occurred… and I got away with it.

Now, decades later, I have this horrible opinion of myself for having contributed to the ignorance of that student and of anyone whom HE might have influenced with regard to this phenomena. God looks after fools and widows I’m told. Sometimes.

For those not familiar with this issue: When Full Flaps on these model airpalnes are deployed, the Down-Wash of relative wind over (under) the leading edge of the horizontal stabilizer brings that stabilizer much closer to a Stall of that flight surface.
Remember that the horizontal tail surfaces behave much like an Upside-Down Wing…. providing Lift in a Downward Direction. This counters the nose-heavy C.G. of an otherwise stabile airplane about the Center of Lift (C/L) provided by the wing. So… the upside-down wing of the horiz. stab. approaches a stall with the downwash of the relative wind created by the application of flaps.

NOw…if the horiz stab is near it’s stalling AOA due to flap application…. and the pilot next applies rudder such as in a slip….the fuselage will “blank” out the opposite side of the horiz stab….and loss of pitch-control may suddenly result as the near-side of the hoiz stab becomes insufficient to maintain the desired pitch.
This occurs suddenly and unexpectedly and unpredictably… and if near the ground may not allow sufficient altitude for a surprised pilot to recover from the resulting sudden pitch-down-and-spin! (The pilot attempting the slip will have applied considerable rudder and opposite aileron to prevent the airplane from rolling….a classic cross-control stall/spin situation.)

There are numerous anecdotes from experienced pilots who I have witnessed making statements that they’ve “done it” lots of times with no bad results.

The pilots who “done it” with bad results…. never seem to be around to make such statements.

I suggest we spread the word and let NO ONE try to convince anyone otherwise. Do Not Slip these airplanes with Full Flaps.

There is a longer discussion of this if you search for NTSB Final Report: Bruce and Kathy Rymes accident -- I cant seem to make it link.

Includes some first hand accounts from those that recovered in time.

Try this link.

thanks

I'd not linked the possibility of a a full flap slip stall to that accident. is there some evidence of a full flap slip connected to this accident?

If you read the other thread you will know I'm one who has gone to altitude to play with this issue. I did it because I was one who was told it was not an issue and had it demonstrated to me. I did it again after installing a VG kit on my 170 which includes VGs under the stabilizer. I wanted to see what effect those VGs may have.

My conclusion was and I've been preaching DO NOT SLIP a B Model with Full Flaps Deployed. EVER. It is not necessary at any risk as with 40° of flaps deployed one can push the nose over into a ridiculously steep angle in trim and not gain appreciable airspeed.

Like George, I've heard lots of pilots poo poo our warning. Claiming loss of elevator control is very easy to control. And I agree you can very easily control the loss, RIGHT UP TO THE TIME YOU DON"T. And if that is a time you're under 3000 AGL or you're above that and you pull into a secondary stall after practically flopping on your back, your SOL.

JUST DON't DO IT.

GAHorn wrote:…
There are numerous anecdotes from experienced pilots who I have witnessed making statements that they’ve “done it” lots of times with no bad results.

The pilots who “done it” with bad results…. never seem to be around to make such statements.

I suggest we spread the word and let NO ONE try to convince anyone otherwise. Do Not Slip these airplanes with Full Flaps.

Other than a near mid-air once, my scariest recollection is having the windshield of my 170B fill with green at 300 ft AGL shortly after initiating a slip with full flaps during a too-high approach to a grass runway. Immediately after the nose dropped I instinctively centered the rudder and, very fortunately for me and my passenger, the airplane recovered itself to a normal attitude JUST in time to flare and land. Had I been 25-50 feet lower the outcome would have been quite different. This was early in my ownership of the airplane so I reread the owner’s manual and found the precaution.

I’m not a CFI, but on rare occasions I have allowed experienced pilots to land ‘98C from the right seat and always admonish them to not to slip with full flaps. In an airplane that can get down as steeply as a170B with full flaps, if you’re still too high to land safely, you’ve already screwed up royally and it’s time to initiate a go-around and come back and try again.

cessna170bdriver wrote: I’m not a CFI, but on rare occasions I have allowed experienced pilots to land ‘98C from the right seat and always admonish them to not to slip with full flaps. In an airplane that can get down as steeply as a170B with full flaps, if you’re still too high to land safely, you’ve already screwed up royally and it’s time to initiate a go-around and come back and try again.

Yep. My feelings as exactly. I do occasionally use full flaps but I hate having all that drag hanging out there if a go around is needed and as you said if you need full flaps AND a slip it's definitely time to re-think your approach.

Thanks for sharing. I too have previously thought maybe this was just a lawyer thing, but do believe it can be quite dangerous as you’ve stated. I only use full flaps on short final with landing assured.

I tried slipping with full flaps at a safe altitude, and sure enough, the nose dropped. I lost 100 feet or so, not too bad, but I’ve never had that happen in any other airplane. It was uncomfortable enough that I stopped slipping the airplane at all. A better way to lose altitude is to throttle back to just above stall warn speed and put out full flaps. You will come down like an elevator.

The early Cessna singles that have 40 degree flap settings really do come down like an elevator, but I think we should keep adequate margin above stall speed. As an instructor, I don’t like to hear the stall warning come on any where in the pattern before the airplane is really close to the runway and in a position to touch down. When I was learning, my instructor demonstrated a full flap spin in a Cessna 150 that I will never forget. (Cessna does not approve of this maneuver, probably for good reason). He put the airplane into a shallow bank like base to final and just stalled it with enough lower rudder to offset the ball in a skid. There was a little squeal of the stall warning but no buffet. The 150 went straight into a rapid, seemingly vertical spin (entry) which required flap retraction in addition to the usual recovery inputs. I remember we recovered after 1 1/2 turns and lost over 1000’ really quickly. This demo was part of my CFI training and made me a believer in maintaining safe approach speeds and rudder coordination.

I am also a believer that slipping a 170B with full flaps is dangerous. However, I wonder if the same hazard exists with half flaps, say when using the side slip technique during approaches in cross winds. This is a preferred configuration for many tailwheel airplanes and I haven’t heard any opinions or recommendations on this. I used to fly a 170A, so it wasn’t an issue. I doubt you need full flaps to land a B model in a crosswind, but does anyone have input on slips with partial flaps or side slips vs forward slips in the B model?

The caution only applies to full flaps (40 degrees) and the caution was eliminated after Cessna reduced the full flap position on Skyhawks (around 1981 If I recall correctly) to 30-degrees.

In strong crosswinds I avoid the use of full flaps entirely and prefer wheel-landings in that situation because I like to keep additional speed for control effectiveness…putting the tail on the ground ASAP in conjunction with aggressive braking. In any case, slipping in crosswinds with less than full flaps shouldn’t be a problem…and I believe Cessnas’ warning still applies in a full-flap crosswind landing….therefore no full flaps in crosswinds.

I have done slips with full flaps. Intentionally even.

The first one, however, was unintentional. I did when my plane was new to me and I was learning it. I generally try not to aggressively make control inputs, and as I gradually increased the control inputs to slip in an effort to correct a high approach, I felt the nose wanting to "tuck". I eased off the control inputs and it was a non-event (other than the long landing).

The next day, I took it up to altitude to do some more slow flight, stalls, and other handling familiarities. I wanted to recreate what I had to see if it was a "feature" or a "bug". Turns out, it's a feature. However, being prepared for it made it a lot easier. I also did not hold it long as it was self-evident it wasn't going to self-correct. It also seemed that elevator back pressure once the tuck began was going to aggravate the situation.

I believe the challenge is quick identification and proper recovery technique. Proper recovery in this instance includes disregarding flight path momentarily so as to correct the aerodynamics of the aircraft. Which means removing all control inputs to neutral and, perhaps most importantly, unloading the airplane. Something I'd imagine goes against survival instinct close to the ground as the nose tucks. I believe it is possible to get away with partial slips, but a change in relative wind due to a gust, especially in a crosswind situation, and you could find yourself exceeding the parameters very quickly. At low altitude, a rapid nose tuck would likely be instinctively corrected by an increase in pressure on the elevator and you may find yourself unable to recover. My suspicion is vertical or inverted with a potential spin developing....

Any situation that involves a stall requires rapid identification and immediate reduction in wing loading...always challenging close to the ground.

This may not be a popular opinion, but when I was doing C170 checkouts in the 170b, I absolutely did full slips with full 40 degree flaps in the practice area.

To demonstrate why you shouldn't. We were loaded in the Utility category, and it was the same flight we did spin recovery.

With an aerobatic background and a strong knowledge of aerodynamics, I can say when the 170b is loaded in the utility, the tail stall is surprising, but not violent, and recovery easy if you do everything opposite of what your instincts tell the average pilot to do, but not necessarily one familiar with aerobatics and aerodynamics.

However, I did it once with the CG a bit further aft, and it was ... highly abrupt (levitated a few things in the back seat). Again, recovery occurs the moment the slip is removed and you reduce the angle of attack on the tail but pushing even more forward, or down toward the green and brown.

Done intentionally, with an experienced CFI, it can be not only eye opening, but really drive home the point why you not only shouldn't forward slip at full flaps, but never land a C170b in a very strong crosswind with full flaps. The side slip and forward slip, to the airplane, aren't different.

YMMV.