Where's the actual spec?
Our EAA chapter had a presentation by our FSDO rep this evening regarding homebuilt certification. One of the items he indicated is that fiber locknuts cannot be reused. I thought I remembered looking this up previously to find the rule "they can be used but only if they can't be tightened by hand" and so I asked him about it.
He indicated the wording on his slide was right out of AC 43.13-1B, Section 4 Paragraph 7-64f:
DO NOT reuse a fiber or nylon locknut
I don't believe he included the rest of the sentence:
, if the nut cannot meet the minimum prevailing torque values (See table 7.2).
Looking at the table provides guidance for large sizes, but not the smaller sizes that are most abundant on our RVs.
Table 7.2:
FINE THREAD SERIES
THREAD SIZE - MINIMUM PREVAILING TORQUE
7/16 - 20 8 inch-pounds
1/2 - 20 10 inch-pounds
9/16 - 18 13 inch-pounds
5/8 -18 18 inch-pounds
3/4 - 16 27 inch-pounds
7/8 - 14 40 inch-pounds
1 - 14 55 inch-pounds
1-1/8 - 12 73 inch-pounds
1-1/4 - 12 94 inch-pounds
COARSE THREAD SERIES
THREAD SIZE - MINIMUM PREVAILING TORQUE
7/16 - 14 8 inch-pounds
1/2 - 13 10 inch-pounds
9/16 - 12 14 inch-pounds
5/8 - 11 20 inch-pounds
3/4 - 10 27 inch-pounds
7/8 - 9 40 inch-pounds
1 - 8 51 inch-pounds
1-1/8 - 8 68 inch-pounds
1-1/4 - 8 88 inch-pounds
You'll notice that nuts less than 7/16 are not listed on the chart. What does that mean? What's the official word?
One interpretation would be: "those smaller sizes have no prevailing torque listed, thus it's impossible to meet it, thus they must not be reused".
Another interpretation would be: "those smaller sizes are not listed, thus there must be no requirement to be met in order to allow reuse".
So does anyone have an official FAA reference? If you google for
fiber nut "unable to tighten" "by hand", you get a lot of hits indicating this is the rule of thumb, but not one of them is an official FAA document.
Inquiring minds want to know.