Sorry that's not the test.

Incidental is a traveling salesman who flies an airplane travel to customers and gets reimbursed by his company.

Not incidental is a traveling salesman who transports company property from the plant to a warehouse

Incidental is (probably) an employee who flies himself and perhaps some co-workers to a conference that the employee attends and has a reason to attend himself.

Not incidental is an employee who transports other company employees to a conference that the employee has no reason to attend himself, especially if he does it regularly

Whether it's incidental or not depends on the nature of the business and the relationship of flying to it, not how the company and the pilot choose to show it on the books in an attempt to avoid the rule.