Crack in the main spar upper cap - What causes it and how to avoid.

It happened not only once that the main spar cap shows a crack in the outer end area.

These cracks are caused by hard landings, resulting in an extra stress or loads on the outer rib of the center section l/r that connects main spar with rear spar:

The loads lead to cracks in either the rib, or worse the main spar.

If you find your spar cracked, there is hope now. Recently a DER signed off a repair recommendation for exactly this problem.

A hard landing can ruin your day, but it does not have to. Alon already recommended years ago a fix to that area to mainly avoid the crack in the ribs, but it also serves as a direct load transfer to the thick part of the main spar and not through the stressed skin and the thin outer part of the spar cap where these cracks happen.

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It is basically an angle made from .063 aircraft grade steel that is rived to the outer rib and is bolted directly to the main spar.