The International Cessna 170 Association

Although the subject of slipping with full flaps had been discussed prior to the loss of Bruce and Kathy, it took that accident to really drive the subject home to me. I think that is probably common where we read about an accident, aviation-boating-motorcycle-automobile, etc.,but when it involves someone we know personally it really gets our attention. I have been guilty of using full flaps and slipping on final approach. Maybe I wasn't slipping to the degree that might result in blanking the horiz stab. After this loss I have been particularly sensitive to the issue and am careful not to do that. Maybe it is overkill on my part, but I now caution all of my friends with whom I am flying or talking flying about not using full flaps and slipping Cessna aircraft. I don't know what the newer 100 series (or 200 series) Cessna data may say regarding the use of flaps and slipping. I checked a copy of my owners manual on the 182 I owned and didn't find any mention of not slipping with full flaps. Although my plane is a '56 172, it has the same warning as B model 170's. Hopefully with all the discussion of Bruce and Kathy's accident a large percentage of our members will become safer pilots. We lost a couple of very fine members in this tragic accident.

170C wrote:Although the subject of slipping with full flaps had been discussed prior to the loss of Bruce and Kathy, it took that accident to really drive the subject home to me. I think that is probably common where we read about an accident, aviation-boating-motorcycle-automobile, etc.,but when it involves someone we know personally it really gets our attention. I have been guilty of using full flaps and slipping on final approach. Maybe I wasn't slipping to the degree that might result in blanking the horiz stab. After this loss I have been particularly sensitive to the issue and am careful not to do that. Maybe it is overkill on my part, but I now caution all of my friends with whom I am flying or talking flying about not using full flaps and slipping Cessna aircraft. I don't know what the newer 100 series (or 200 series) Cessna data may say regarding the use of flaps and slipping. I checked a copy of my owners manual on the 182 I owned and didn't find any mention of not slipping with full flaps. Although my plane is a '56 172, it has the same warning as B model 170's. Hopefully with all the discussion of Bruce and Kathy's accident a large percentage of our members will become safer pilots. We lost a couple of very fine members in this tragic accident.

Cessna limited flap travel to 30 degrees in the later production airplanes for this reason.

Aryana wrote:My buddies 70's era 172 had the flaps limited to 30 degrees when he installed a 180 hp engine under an STC. I wonder what that had to do with the HP of the engine?

There are other reasons Cessna limited flap movement in later aircraft having all to do with other certification limits, and having anything to do eliminating the elevator stall issue. Though the restricted movement and the increased area of the elevator, seemed to fix this issue as well as we don't hear of it being a characteristic of the later model 172.

At the risk of repeating ourselves:.... the Owner's Manual is not an approved document. It was produced by the sales dept. and therefore anything regarding flight characteristics, including warnings, were seen as recommendations. This unfortunate circumstance resulted in such a low-key placard.

Cessna engineering test pilot and flight test/aerodynamics manager W.D. Thompson, author of Cessna: Wings for the World (pg.41) discussed the problem as late as the 1972 Cessna 172-L model, and he mentions that it applied to all 170, 180, and 172 aircraft up to that model. He mentions that in some instances the problem was severe enough to lift the pilot against the seat-belt!
Cessna vertical and horizontal stabilizers were given increased span/height to decrease the problem, but he states "we privately encouraged flight instructors to explore these effects at high altitude, and to pass on the information to their students. The phenomenon was elusive and sometimes hard to duplicate...."
Even after larger tail surfaces were installed there still was experienced a "mild, pitch 'pumping' motion resulting from flap outboard-end vortex impingement on the horizontal tail at some combinations of side-slip..."

The phenomenon only occurs at flap settings greater than 30-degrees, and later airplanes were limited to that flap setting for several reasons (including balked-landing-climb certification climb requirements and to reduce stresses placed upon the rear door-post as gross weights were increased) which made the warning become moot.
Unfortunately, pilots who gain their experience in later airplane models (and even some long-time/experienced owners of 170B and 172 aircraft will argue against the warning as rumor.) They can fail to learn of this the hard way.

That report is pretty standard for the NTSB. They never speculate. They will only assign a specific probable cause if there's direct, factual evidence for it. There is no direct evidence that they slipped the airplane with full flaps, even though for pilots familiar with that flight characteristic of 170s, the circumstantial evidence is powerful.

Type clubs gather knowledge and wisdom unavailable to the NTSB and the modern-day FAA. That's why a good type club is so important; our 170 Association is one of the best, and if you're a non-member with an interest in 170s reading this, you really owe it to yourself to join.

NTSB reports often can't pinpoint the cause of an accident, but they're still valuable. If you've never done it before, try searching the database for accidents involving 170s, and read all the summaries over the last 5 or 10 years. When you start to see patterns, go back and start a tally of accidents with certain characteristics. (Go to http://www.ntsb.gov/aviationquery/, enter "CESSNA" and "170" for Make and Model in the query form, then click on "Submit Query.")

I did this for my J-3 Cub a few years ago, and was quite surprised by what I saw. (Nonfatal departure stall/spin accidents, for one. And a pattern of engine failures caused by failure of a $30 clamp that holds the throttle cable to the engine mount -- or by substitution of a non-approved replacement for that part. I think there were five of those.)

Fly safely!