10 Degree Flap Modification 1954 C-170B

[C-FCWG]

Hello All:
I'm looking to modify my flaps to allow a 10 degree setting. I have access to an official part however the 54 is not listed as having 10 degrees. POH is clear about that. Cessna says it is not approved but I have "friends" who have modified their planes accordingly. Does anyone have any studies, paperwork or such allowing this modification? My AME is reluctant to do this due to liability, and I've been told that if this ratchet was inspected and found to be "cracked" and we replaced it with the right part number (those didn't change regardless of the year - also fun fact, same part in a 180/185) with 10 degree notch from a 56 or a 56-62 172, it wouldn't be an issue as long as Transport doesn't take a long hard look.

Any help or direction would be appreciated.

[c170b53]

viewtopic.php?f=24&t=13787&p=130038&hil ... or#p130038 See this post.
Search within the site with the search function is your friend. Welcome fellow Canadian to the association, thanks for being part of the family. Where are you based ?

[GAHorn]

If one were to “dot the i’s and cross the T’s”…. I believe it would me most correct to replace the early sector with the later sector….as that would not require the alteration of an existing early sector….which would add the complication of a “basis of approval” as well as documentation as to how the modification was accomplished. (all of which is very minor, IMO)

I obtained a N.O.S. later ratchet and installed it. Does it make any difference other than “in my mind”..?

No. The performance data does not change. So, why did I do it?

For the same reason anyone does…. I seems better to have more choices. But 20-degrees of flaps is more likely to get you off the ground sooner (reduce ground run) at the penalty of hurting you more in the climb to the obstacle. Either way, Cessna says the 20-degree flap performance data to clear the obstacle is the same.

One more case of “measure it with a micrometer, mark it with a grease-pencil, cut it with a hatchet”.

Other than changing an incandescent lamp to a L.E.D. lamp…this is probably the easiest mod one can make. (Virtually a Drop-in part.)

[GAHorn]

The Type Certificate Data Sheet (Rev 54 and 55) does indeed offer “Approval” for the 10-degree flat sector/ratchet for early B-models. However, in another example of misdirection, the IPC (prior to the January 1995 Revision) offered it “when supplies are exhausted” of the early PN. After the 1995 Revision, confusion was added when the notation offered only a 10/20/30/40 degree ratchet and specified that it must be ordered whenever the flap lever is replaced. (using ** for the notation). I do not understand why a new flap lever would require a new ratchet, but there it is.

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