Which wood defect always requires rejection?

The defect that always requires rejection is decay. Decay in wood refers to the deterioration caused by fungi, which breaks down the wood fibers and compromises its structural integrity. When wood is decayed, it loses its strength and load-bearing capacity, making it unsuitable for any applications, especially in aviation where safety and reliability are paramount. Structures made from decayed wood can be at a high risk of failure, thus rendering this type of defect unacceptable.

While worm holes, spike knots, and honeycomb can affect the wood's performance and aesthetics, they may not necessarily render the wood unusable, depending on the severity and context. For instance, minor worm holes may be acceptable in some applications, and spike knots could potentially be worked around or positioned in low-stress areas. Honeycomb can also be assessed for its impact on strength and may sometimes be repaired or mitigated in certain uses. However, decay is an irreversible condition that completely undermines the viability of the wood, necessitating its rejection from use entirely.