Which wood condition always requires repair or replacement?

Compression failure refers to a condition in wood where the material has been subjected to excessive load, leading to crushed fibers in the wood structure. This situation compromises the structural integrity of the wood used in aviation applications, making it unable to perform its intended function safely. When compression failure occurs, it generally means that the wood can no longer provide the necessary support and strength. Therefore, it must be repaired or replaced to ensure the safety and reliability of the aircraft components made from that wood.

In contrast, surface irregularities, discoloration, and surface checking may not always necessitate immediate repair or replacement. Surface irregularities can often be smoothed out, discoloration may primarily be cosmetic without affecting structural strength, and surface checking may be assessed for severity. Each of these conditions requires evaluation, but they do not inherently compromise the integrity of the wood as compression failure does.