Which terms are used in aviation documents to convey optional compliance?

In aviation documents, terms that convey optional compliance are "may" and "can." These terms indicate that an action is permissible but not mandatory. For instance, when a document states that a pilot may use a particular procedure or can perform a certain action, it suggests that the pilot has the discretion to choose whether or not to follow that guidance, implying it is not compulsory.

In contrast, other terms like "shall," "must," and "will" typically impose requirements or obligations, indicating that something is mandatory. The use of "ought" and "should" suggests a recommendation rather than an optional choice and may imply a level of expectation or advisable action. Therefore, "may" and "can" are the correct choices as they explicitly denote flexibility in compliance within aviation regulations and procedures.