The International Cessna 170 Association

I have looked through some other threads regarding issues with the flap handles, but I did not see one regarding this particular problem. On my '48 170, the flap handle button has a failure mode where the button will not release. The problem seems to be that the pawl has retracted past the pin that is supposed to stop it, and then won't go back. As a consequence, the flaps cannot be deployed, because the pawl will not move down to hold them in position. My A&P has fixed this once, and it happened again today. He wasn't sure how it happened, because it did not appear to him that the pawl could move past the pin on its own. He did not observe anything obviously worn. It does not appear to be the same issue that can cause the pawl to become stuck when the flaps are extended.

Has anyone else experienced this particular failure or have any ideas on which parts might be causing the problem, or do I need to replace the whole assembly? As always, TIA.

An entire replacement would not be necessary. You have to figure out what's happening with yours and repair it. After all how would you know the replacement 70 year old part wouldn't do the same thing?

What pin?

Looking at that drawing and the drawing for the 170A, it appears I possibly have some mismatched parts.

The handle is definitely the 48 handle. But the pawl matches the 170A drawing, which looks slightly different from the 48 drawing. It has a pronounced tab on the top that the actuating rod hooks into, and that tab seems to have worn a spot on the rivet above the top pivot that retains the spring, such that it can pass it but not return. And the pawl appears to be riveted in, rather than riding on a bolt.

Also, the pivot for the handle passes through the whole channel, not just the housing.

I was able to force the pawl back into position, but I think at least that worn rivet needs to be replaced. Should I also replace the pawl if this is indeed the wrong part?

Pics (click for larger):

Before



After

As you can see the flap lever assembly between the 170 and the 170 A is not the same by part number and the lever itself has a different number. However the latch assembly inside each of the levers is the same part number for part number.

Another interesting fact though. Each model 170, 170A and 170B has it's own different flap handle.

Thanks Bruce. Interesting that they're the same parts but the drawings look so different. The return spring also. So it seems that I have all the right parts, but at some point the latch pivot bolt was replaced with the bushing and rivit. Hopefully replacing that upper rivet will fix it up.

I love the Fowler Flaps on C 170

Your button sticks down and unable to deploy flaps. Has this happened in flight?

Did you have to do forward slip to adjust landing approach?

Please tell us?

My 48 does the same. You can live with it as is provided you use only very slight thumb pressure on the button, just enough to release and retract the flap. If you use to much thumb power it snags the the flap handle internals. Otherwise reworking may be required. I manage mine that way.

If I get back to the airplane this week I will take a video of the issue, or at least some pictures for you. As I said my 48 has the same issue....basically light thumb pressure to the lock plunger or just enough to glide over the flap ratchet detent and it shouldn’t jam. Flapless landings are no issue in the 48 if you jam the latch. Once safety on the ground deploy the flap handle fully and reach down and manually reposition the lock tab with a screw driver or fuel sampler screwdriver end. I just love 70 year old airplanes!

MoonlightVFR wrote:I love the Fowler Flaps on C 170

Your button sticks down and unable to deploy flaps. Has this happened in flight?

Did you have to do forward slip to adjust landing approach?

Please tell us?

As Poncho says, the flaps are not necessary. In my limited experience with the plane so far, slipping is at least as effective as the flaps if a steeper approach is desired, but it comes down pretty well with power off.

Luckily my 48 has not had the problem. I did have it happen on my VW bug emergency (hand brake)brake years ago. On that one, the plate with the position detents just flipped too far and I had to dismantle it and put it in proper position. Then, to never snap push the button again. Was a simple dismantle. Nuff.

I'd like to remind Members that the Flap Control failure can be a DEADLY event in some circumstances. Scenario: OK... you discover the flap button sticks in a depressed position...but you elect to go fly anyway without flaps. Later on, while making an approach...you decide to give it another try and ....VOILA!... FULL flaps work PERFECTLY!

Now someone pulls out in front of you ...and you must go around...but WAIT... THE FLAPS WILL NOT RETRACT!

This exact scenario killed two occupants at Boeing Field as reported directly to us by an NTSB Investigator who was concerned that those who operate aircraft with Manual Flaps have the attitude they are much simpler and more reliable than electric flaps in later models. NOT SO. A low-powered aircraft like most single Cessna's are reluctant to go-around with full flaps deployed.

See the MX Library threads:
http://cessna170.org/forums/viewtopic.php?f=32&t=2231
and
http://cessna170.org/forums/viewtopic.php?f=32&t=6460