The tail section vertical spar bottom end is attached to the V-frame with an AN-3 bolt. During ground operations with the engine idling, there are considerable vibrations. These can eventually lead to this problem. A hairline crack can develop between the bolt hole and the bottom of the vertical spar. See AD 59-22-03. At the next annual inspection, or whenever you get a chance, take a close look at this area. 

What to do:

Being aware of this problem, several Mite owners in the Los Angeles area have developed a fix. Besides the normal procedure of re-gluing the crack and maybe installing mahogany reinforcing plates on both sides of the lower section of the spar, we manufacture a U-shaped (actually more like a tapered U-bracket, since the bottom of the vertical spar is tapered), wrap-around bracket of 4130 steel (see below)..

This bracket will hold the lower portion of the spar in position, and not depend on the bolt alone to do the job. 

This procedure has worked well, and we have not seen any cracks since this bracket was installed.

Submitted by Ben Favrholdt, N66MX

Installing a vertical spar reinforcing bracket:

Drawing of bracket assembly (oriented sideways for printing)

Instructions: after the bracket is fabricated, remove the tail stinger or at least detach it enough to have working room for fitting the bracket to the fin lower spar. Otherwise it is a tight squeeze for one's hands to do the job properly. Good common sense should apply. Another word of advice: if the spar is found to be cracked, it should be repaired first, before installation of the bracket.

Submitted by Tony Terrigno, N120C