How many months is a TSO allowed to remain in effect beyond its effective date?

A TSO, or Technical Standard Order, is a minimum performance standard for specified materials, parts, and appliances used on civil aircraft. Once a TSO is issued and becomes effective, it can remain in effect for a maximum of six months beyond its effective date during which it is generally expected that the applicable documents or guidance will be kept updated or reviewed for relevance. This six-month period allows for modifications or changes to be introduced if necessary while still providing a buffer for manufacturers and users who are still adhering to the previous but now-expired version of the TSO.

This duration helps ensure that safety and compliance standards are maintained while providing a transitional period for updates and adaptations to the changes in regulations or technology. Therefore, the six-month duration is the correct measure established for the longevity of a TSO effectively meaning it remains valid and in use until an alternative is fully adopted or implemented.