repitching a prop from a regulatory standpoint

[futr_alaskaflyer]

OK, after reading a few past threads I am a bit confused...

From a regulatory standpoint, what is needed to repitch your existing prop?

(Yes, yes, George, I have read the TCDS!)

I am thinking that if your static RPM still remains within allowed limits on the TCDS, vs it being now outside those limits, I would imagine it would make a difference from a paperwork standpoint. But what is that

Theoretically, all those 170's out there with props repitched to 55 and 51 have 337 field approvals on file, or what?

[GAHorn]

Prop repitching is a major alteration/repair which may only be performed by the Mfr or CRS (prop shop) in accordance with approved data. The Mfr specifies how much a prop may be repitched. The TCDS specifies the rpm (and therefore limits the amount of repitching) which may be applied to a prop that is installed on a 170. The latter condition is in order to avoid violating the certification of both airplane AND engine limits while still meeting performance standards.
In other words, McCauley MAY allow the DM 7653 to be repitched all the way to 30...but if that allows the takeoff rpm of the engine to exceed 2700 rpm it would violate the engine limit and the TCDS of both engine and airplane (because the engine would be overspeeding and the airplane would be subjected to unapproved horsepower increases with that engine installation. There may also be other considerations such as vibration problems at rpms which the engine and engine mount is unapproved.)
In other words...Don't try this at home!

[Bruce Fenstermacher]

George
Perhaps you where just not being specific when you say only the manufacturer or a CRS but wouldn't an A&P mechanic with the proper tools and prop service manuals technically be able to repitch a prop?

[futr_alaskaflyer]

OK,

So...what are those with a 51 pitch prop seeing on their static RPM? Surely it is more than 2330?

And so I'm sure I have this right...a repitch that keeps the prop within the static rpm limits of the TCDS requires a 337 to be sent in for the file like any major repair; while one that sends the static rpm outside the authorized limits requires a field or other official approval?

[GAHorn]

Good catch, Bruce. I answered hastily. Actually, I don't have it just in front of me, but if I recall correctly it's similar to the situation with geared engines,... I think it takes at least an A&P with IA. (I'll ask the FAA today while I'm at work.)

[Bruce Fenstermacher]

Richard

Here is the way I understand it. Your prop must be an approved model for the aircraft engine combination. Approved either by the TCDS, STC or one time approval.

The prop must meet it's own TCDS or limits set by an approval method mentioned in the first paragraph. There are usually max and minimum diameters and possibly pitch angel limitations. I can not remember seeing pitch limits just static rpm limits.

So you could have someone who is approved, using approved methods and practices following the prop manufactures service manual change your prop in any regard (usually pitch) so long as it meets the criteria of my first two paragraphs, then make a log book entry in both the prop log and the aircraft log stating the changes and that is it.

If you deviate from compiling with any part of the my first two paragraphs then there would be a major alteration of either the aircraft, prop or both and you would need an approved 337 for it as well as the log book entries.

Here is a likely scenario.

You fly your airplane to a prop shop which most likely is a Certified Repair Station. A A&P will remove and inspect your prop to make sure that it meets it's TCDS. He should make sure that any work you request will meet the prop and the aircraft TCDS or another basis of approval then re-pitch or shorten the prop to accomplish what you desire.

He will reinstall the prop, and in the case of static rpms limits, test the prop airplane combination, then assuming all is well, make log book entries in the prop and aircraft logs stating the work performed and the basis of it's approval.

You fly home.

[GAHorn]

...So you could have someone who is approved, ...

I asked our DM at work today and he affirmed that FAR 43.13 is the proper guidance and that it would take at least an A&P/IA to approve the prop for return to service after the prop was repitched (IF it was done IAW mfr and 43.13 ...that being a major alteration.) In other words this is not an operation which should be undertaken by an owner or an adventurous A&P without the proper toos, manuals, using the approved methods, etc., and having the authority to return it to service.
Virtually no knowlegeable A&P will undertake this task and will insist that the prop be sent out to the mfr or CRS. (in his opinion) I agree.

Most prop mfr's limit the amount of repitching and the number of times a prop may be repitched before it is rendered permanently unairworthy. (This is another possible problem with buying parts with incomplete records from unknown sources.)

[ron74887]

Damn I guess this means you can't take a 36 and cheater pipe and add twist using a rubber cushing between the teeth and the prop to keep the teeth from damaging the prop during torqueing. about a 10 foot cheater is appropiate. i'd add emoticons but don't know how kinda like repitching a prop. On the TCDs they give you std climb and cruise but I don't know if that is concrete. Ron