Aircraft with a Vne of 135 mph or less are considered to be unairworthy when the fabric breaking strength has deteriorated to below ___________?

In the context of fabric covering for aircraft, the term "Vne" refers to the "never exceed" speed, indicating the maximum allowable airspeed for the aircraft. If the fabric covering has deteriorated in strength, it poses a significant risk to the aircraft’s structural integrity and safety during flight.

When it comes to aircraft with a Vne of 135 mph or less, specific standards have been established regarding the fabric’s breaking strength to ensure safety. The correct threshold is 35 pounds of breaking strength per square inch. This means that if the fabric's strength falls below this value, the aircraft is deemed unairworthy. Maintaining the fabric's strength above this threshold is crucial, as deterioration can compromise the safety of the aircraft and its occupants.

Other choices would not provide sufficient strength to ensure the aircraft remains airworthy under operational conditions, especially as speed and stress increase during flight. Hence, maintaining the fabric strength at or above 35 pounds is essential for safe operation.