Fabric is considered unairworthy when it has deteriorated to what percentage of its original strength?

• A. 60%
• B. 65%
• C. Less than 70%
• D. 75%

Answer: (C)

Fabric coverings must retain enough strength to safely carry flight loads. The airworthiness standard uses a 70% threshold of the original tensile strength as the cutoff. If the fabric’s current strength falls below 70% of what a new fabric would have, it no longer provides the required safety margin and is considered unairworthy. So, when the fabric deteriorates to less than 70% of its original strength, it must be replaced. A value like 75% would still meet the requirement, while 60% or 65% would already be below the threshold, underscoring why the correct criterion is “less than 70%.”